Systemic lupus erythematosus (SLE), also known simply as lupus, is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body.[1] Symptoms vary between people and may be mild to severe.[1] Common symptoms include painful and swollen joints, fever, chest pain, hair loss, mouth ulcers, swollen lymph nodes, feeling tired, and a red rash which is most commonly on the face.[1] Often there are periods of illness, called flares, and periods of remission during which there are few symptoms.[1]
The cause of SLE is not clear.[1] It is thought to involve genetics together with environmental factors.[4] Among identical twins, if one is affected there is a 24% chance the other one will be as well.[1] Female sex hormones, sunlight, smoking, vitamin D deficiency, and certain infections, are also believed to increase the risk.[4] The mechanism involves an immune response by autoantibodies against a person's own tissues.[1] These are most commonly anti-nuclear antibodies and they result in inflammation.[1] Diagnosis can be difficult and is based on a combination of symptoms and laboratory tests.[1] There are a number of other kinds of lupus erythematosus including discoid lupus erythematosus, neonatal lupus, and subacute cutaneous lupus erythematosus.[1]
There is no cure for SLE.[1] Treatments may include NSAIDs, corticosteroids, immunosuppressants, hydroxychloroquine, and methotrexate.[1] Alternative medicine has not been shown to affect the disease.[1] Life expectancy is lower among people with SLE.[5] SLE significantly increases the risk of cardiovascular disease with this being the most common cause of death.[4] With modern treatment about 80% of those affected survive more than 15 years.[3] Women with lupus have pregnancies that are higher risk but are mostly successful.[1]
Rate of SLE varies between countries from 20 to 70 per 100,000.[2] Women of childbearing age are affected about nine times more often than men.[4] While it most commonly begins between the ages of 15 and 45, a wide range of ages can be affected.[1][2] Those of African, Caribbean, and Chinese descent are at higher risk than white people.[4][2] Rates of disease in the developing world are unclear.[6] Lupus is Latin for "wolf": the disease was so-named in the 13th century as the rash was thought to appear like a wolf's bite
SLE is one of several diseases known as "the great imitator" because it often mimics or is mistaken for other illnesses.[9] SLE is a classical item in differential diagnosis,[10] because SLE symptoms vary widely and come and go unpredictably. Diagnosis can thus be elusive, with some people having unexplained symptoms of SLE for years.
Common initial and chronic complaints include fever, malaise, joint pains, muscle pains, and fatigue. Because these symptoms are so often seen in association with other diseases, these signs and symptoms are not part of the diagnostic criteria for SLE. When occurring in conjunction with other signs and symptoms, however, they are considered suggestive.[11]
While SLE can occur in both males and females, it is found far more often in women, and the symptoms associated with each sex are different.[5] Females tend to have a greater number of relapses, a low white blood cell count, more arthritis, Raynaud's phenomenon, and psychiatric symptoms. Males tend to have more seizures, kidney disease, serositis (inflammation of tissues lining the lungs and heart), skin problems, and peripheral neuropathy.[12]
Skin
As many as 70% of people with lupus have some skin symptoms. The three main categories of lesions are chronic cutaneous (discoid) lupus, subacute cutaneous lupus, and acute cutaneous lupus. People with discoid lupus may exhibit thick, red scaly patches on the skin. Similarly, subacute cutaneous lupus manifests as red, scaly patches of skin but with distinct edges. Acute cutaneous lupus manifests as a rash. Some have the classic malar rash (or butterfly rash) associated with the disease.[13] This rash occurs in 30 to 60% of people with SLE.[14]
Hair loss, mouth and nasal ulcers, and lesions on the skin are other possible manifestations.[15]
Muscles and bones
The most commonly sought medical attention is for joint pain, with the small joints of the hand and wrist usually affected, although all joints are at risk. More than 90 percent of those affected will experience joint or muscle pain at some time during the course of their illness.[16] Unlike rheumatoid arthritis, lupus arthritis is less disabling and usually does not cause severe destruction of the joints. Fewer than ten percent of people with lupus arthritis will develop deformities of the hands and feet.[16] People with SLE are at particular risk of developing osteoarticular tuberculosis.[17]
A possible association between rheumatoid arthritis and SLE has been suggested,[18] and SLE may be associated with an increased risk of bone fractures in relatively young women.[19]
Blood
Anemia is common in children with SLE[20] and develops in about 50% of cases.[21] Low platelet and white blood cell counts may be due to the disease or a side effect of pharmacological treatment. People with SLE may have an association with antiphospholipid antibody syndrome[22] (a thrombotic disorder), wherein autoantibodies to phospholipids are present in their serum. Abnormalities associated with antiphospholipid antibody syndrome include a paradoxical prolonged partial thromboplastin time (which usually occurs in hemorrhagic disorders) and a positive test for antiphospholipid antibodies; the combination of such findings have earned the term "lupus anticoagulant-positive". Another autoantibody finding in SLE is the anti-cardiolipin antibody, which can cause a false positive test for syphilis.[citation needed]
Heart
SLE may cause pericarditis—inflammation of the outer lining surrounding the heart, myocarditis—inflammation of the heart muscle, or endocarditis—inflammation of the inner lining of the heart. The endocarditis of SLE is non-infectious, and is also called (Libman–Sacks endocarditis). It involves either the mitral valve or the tricuspid valve. Atherosclerosis also occurs more often and advances more rapidly than in the general population.[23][24]
Lungs
SLE can cause pleuritic pain as well as inflammation of the pleurae known as pleurisy, which can rarely give rise to shrinking lung syndrome involving a reduced lung volume.[25][26] Other associated lung conditions include pneumonitis, chronic diffuse interstitial lung disease, pulmonary hypertension, pulmonary emboli, and pulmonary hemorrhage.
Kidneys
Painless passage of blood or protein in the urine may often be the only presenting sign of kidney involvement. Acute or chronic renal impairment may develop with lupus nephritis, leading to acute or end-stage kidney failure. Because of early recognition and management of SLE, end-stage renal failure occurs in less than 5%[27][28] of cases; except in the black population, where the risk is many times higher.
The histological hallmark of SLE is membranous glomerulonephritis with "wire loop" abnormalities.[29] This finding is due to immune complex deposition along the glomerular basement membrane, leading to a typical granular appearance in immunofluorescence testing.
Neuropsychiatric
Further information: Neuropsychiatric systemic lupus erythematosus
Neuropsychiatric syndromes can result when SLE affects the central or peripheral nervous system. The American College of Rheumatology defines 19 neuropsychiatric syndromes in systemic lupus erythematosus.[30] The diagnosis of neuropsychiatric syndromes concurrent with SLE (now termed as NPSLE),[31] is one of the most difficult challenges in medicine, because it can involve so many different patterns of symptoms, some of which may be mistaken for signs of infectious disease or stroke.[32]
A common neurological disorder people with SLE have is headache,[33] although the existence of a specific lupus headache and the optimal approach to headache in SLE cases remains controversial.[34] Other common neuropsychiatric manifestations of SLE include cognitive dysfunction, mood disorder, cerebrovascular disease,[33] seizures, polyneuropathy,[33] anxiety disorder, psychosis, depression, and in some extreme cases, personality disorders.[35] Steroid psychosis can also occur as a result of treating the disease.[31] It can rarely present with intracranial hypertension syndrome, characterized by an elevated intracranial pressure, papilledema, and headache with occasional abducens nerve paresis, absence of a space-occupying lesion or ventricular enlargement, and normal cerebrospinal fluid chemical and hematological constituents.[36]
More rare manifestations are acute confusional state, Guillain–Barré syndrome, aseptic meningitis, autonomic disorder, demyelinating syndrome, mononeuropathy (which might manifest as mononeuritis multiplex), movement disorder (more specifically, chorea), myasthenia gravis, myelopathy, cranial neuropathy and plexopathy.
Neurological disorders contribute to a significant percentage of morbidity and mortality in people with lupus.[37] As a result, the neural side of lupus is being studied in hopes of reducing morbidity and mortality rates.[30] One aspect of this disease is severe damage to the epithelial cells of the blood–brain barrier. In certain regions, depression affects up to 60% of women with SLE.[38]
Eyes
Eye involvement is seen in up to one-third of people. The most common diseases are dry eye syndrome and secondary Sjögren's syndrome, but episcleritis, scleritis, retinopathy (more often affecting both eyes than one), ischemic optic neuropathy, retinal detachment, and secondary angle-closure glaucoma may occur. In addition, the medications used to treat SLE can cause eye disease: long-term glucocorticoid use can cause cataracts and secondary open-angle glaucoma, and long-term hydroxychloroquine treatment can cause vortex keratopathy and maculopathy.[39]
Reproductive
Further information: Systemic lupus erythematosus and pregnancy
SLE causes an increased rate of fetal death in utero and spontaneous abortion (miscarriage). The overall live-birth rate in people with SLE has been estimated to be 72%.[40] Pregnancy outcome appears to be worse in people with SLE whose disease flares up during pregnancy.[41]
Neonatal lupus is the occurrence of SLE symptoms in an infant born from a mother with SLE, most commonly presenting with a rash resembling discoid lupus erythematosus, and sometimes with systemic abnormalities such as heart block or enlargement of the liver and spleen.[42] Neonatal lupus is usually benign and self-limited.[42]
Systemic
Fatigue in SLE is probably multifactorial and has been related to not only disease activity or complications such as anemia or hypothyroidism, but also to pain, depression, poor sleep quality, poor physical fitness and lack of social support.[43][44]
Causes
SLE is presumably caused by a genetic susceptibility coupled with an environmental trigger which results in defects in the immune system. One of the factors associated with SLE is vitamin D deficiency.[45]
Genetics
SLE does run in families, but no single causal gene has been identified. Instead, multiple genes appear to influence a person's chance of developing lupus when triggered by environmental factors. HLA class I, class II, and class III genes are associated with SLE, but only classes I and II contribute independently to increased risk of SLE.[46] Other genes which contain risk variants for SLE are IRF5, PTPN22, STAT4,[47] CDKN1A,[48] ITGAM, BLK,[47] TNFSF4 and BANK1.[49] Some of the susceptibility genes may be population specific.[47] Genetic studies of the rates of disease in families supports the genetic basis of this disease with a heritability of >66%.[50] Identical (monozygotic) twins were found to share susceptibility to the disease at >35% rate compared to fraternal (dizygotic) twins and other full siblings who only showed a 2–5% concordance in shared inheritance.[50]
Since SLE is associated with many genetic regions, it is likely an oligogenic trait, meaning that there are several genes that control susceptibility to the disease.[51]
SLE is regarded as a prototype disease due to the significant overlap in its symptoms with other autoimmune diseases.[52]
Drug reactions
Drug-induced lupus erythematosus is a (generally) reversible condition that usually occurs in people being treated for a long-term illness. Drug-induced lupus mimics SLE. However, symptoms of drug-induced lupus generally disappear once the medication that triggered the episode is stopped. More than 38 medications can cause this condition, the most common of which are procainamide, isoniazid, hydralazine, quinidine, and phenytoin.[53][10]
Non-systemic forms of lupus
Discoid (cutaneous) lupus is limited to skin symptoms and is diagnosed by biopsy of rash on the face, neck, scalp or arms. Approximately 5% of people with DLE progress to SLE.[54]
Pathophysiology
SLE is triggered by environmental factors that are unknown. In SLE, the body's immune system produces antibodies against itself, particularly against proteins in the cell nucleus. These antibody attacks are the immediate cause of SLE.[10][55][56]
SLE is a chronic inflammatory disease believed to be a type III hypersensitivity response with potential type II involvement.[57] Reticulate and stellate acral pigmentation should be considered a possible manifestation of SLE and high titers of anti-cardiolipin antibodies, or a consequence of therapy.[58]
People with SLE have intense polyclonal B-cell activation, with a population shift towards immature B cells. Memory B cells with increased CD27+/IgD—are less susceptible to immunosuppression. CD27-/IgD- memory B cells are associated with increased disease activity and renal lupus. T cells, which regulate B-cell responses and infiltrate target tissues, have defects in signaling, adhesion, co-stimulation, gene transcription, and alternative splicing. The cytokines B-lymphocyte stimulator (BLys), interleukin 6, interleukin 17, interleukin 18, type I interferons, and tumor necrosis factor α (TNFα) are involved in the inflammatory process and are potential therapeutic targets.[4][59][60]
In the complement system low C3 levels are associated with systemic lupus erythematosus[61]
Cell death signaling
Apoptosis is increased in monocytes and keratinocytes
Expression of Fas by B cells and T cells is increased
There are correlations between the apoptotic rates of lymphocytes and disease activity.
Necrosis is increased in T lymphocytes.
Tingible body macrophages (TBMs) – large phagocytic cells in the germinal centers of secondary lymph nodes – express CD68 protein. These cells normally engulf B cells that have undergone apoptosis after somatic hypermutation. In some people with SLE, significantly fewer TBMs can be found, and these cells rarely contain material from apoptotic B cells. Also, uningested apoptotic nuclei can be found outside of TBMs. This material may present a threat to the tolerization of B cells and T cells. Dendritic cells in the germinal center may endocytose such antigenic material and present it to T cells, activating them. Also, apoptotic chromatin and nuclei may attach to the surfaces of follicular dendritic cells and make this material available for activating other B cells that may have randomly acquired self-specificity through somatic hypermutation.[62] Necrosis, a pro-inflammatory form of cell death, is increased in T lymphocytes, due to mitochondrial dysfunction, oxidative stress, and depletion of ATP.[63]
Clearance deficiency
Impaired clearance of dying cells is a potential pathway for the development of this systemic autoimmune disease. This includes deficient phagocytic activity and scant serum components in addition to increased apoptosis.
SLE is associated with defects in apoptotic clearance, and the damaging effects caused by apoptotic debris. Early apoptotic cells express “eat-me” signals, of cell-surface proteins such as phosphatidylserine, that prompt immune cells to engulf them. Apoptotic cells also express “find-me” signals, to attract macrophages and dendritic cells. When apoptotic material is not removed correctly by phagocytes, they are captured instead by antigen-presenting cells, which leads to development of antinuclear antibodies.[4]
Monocytes isolated from whole blood of people with SLE show reduced expression of CD44 surface molecules involved in the uptake of apoptotic cells. Most of the monocytes and tingible body macrophages (TBMs), which are found in the germinal centres of lymph nodes, even show a definitely different morphology; they are smaller or scarce and die earlier. Serum components like complement factors, CRP, and some glycoproteins are, furthermore, decisively important for an efficiently operating phagocytosis. With SLE, these components are often missing, diminished, or inefficient.
Recent research has found an association between certain people with lupus (especially those with lupus nephritis) and an impairment in degrading neutrophil extracellular traps (NETs). These were due to DNAse1 inhibiting factors, or NET protecting factors in people's serum, rather than abnormalities in the DNAse1 itself.[64] DNAse1 mutations in lupus have so far only been found in some Japanese cohorts.[65]
The clearance of early apoptotic cells is an important function in multicellular organisms. It leads to a progression of the apoptosis process and finally to secondary necrosis of the cells if this ability is disturbed. Necrotic cells release nuclear fragments as potential autoantigens, as well as internal danger signals, inducing maturation of dendritic cells (DCs), since they have lost their membranes' integrity. Increased appearance of apoptotic cells also stimulates inefficient clearance. That leads to maturation of DCs and also to the presentation of intracellular antigens of late apoptotic or secondary necrotic cells, via MHC molecules. Autoimmunity possibly results by the extended exposure to nuclear and intracellular autoantigens derived from late apoptotic and secondary necrotic cells. B and T cell tolerance for apoptotic cells is abrogated, and the lymphocytes get activated by these autoantigens; inflammation and the production of autoantibodies by plasma cells is initiated. A clearance deficiency in the skin for apoptotic cells has also been observed in people with cutaneous lupus erythematosus (CLE).[66]
Germinal centers
In healthy conditions, apoptotic lymphocytes are removed in germinal centers (GC) by specialized phagocytes, the tingible body macrophages (TBM), which is why no free apoptotic and potential autoantigenic material can be seen. In some people with SLE, build up of apoptotic debris can be observed in GC because of an ineffective clearance of apoptotic cells. In close proximity to TBM, follicular dendritic cells (FDC) are localised in GC, which attach antigen material to their surface and, in contrast to bone marrow-derived DC, neither take it up nor present it via MHC molecules.
Autoreactive B cells can accidentally emerge during somatic hypermutation and migrate into the germinal center light zone. Autoreactive B cells, maturated coincidentally, normally do not receive survival signals by antigen planted on follicular dendritic cells and perish by apoptosis. In the case of clearance deficiency, apoptotic nuclear debris accumulates in the light zone of GC and gets attached to FDC. This serves as a germinal centre survival signal for autoreactive B-cells. After migration into the mantle zone, autoreactive B cells require further survival signals from autoreactive helper T cells, which promote the maturation of autoantibody-producing plasma cells and B memory cells. In the presence of autoreactive T cells, a chronic autoimmune disease may be the consequence.
Anti-nRNP autoimmunity
Anti-nRNP autoantibodies to nRNP A and nRNP C initially targeted restricted, proline-rich motifs. Antibody binding subsequently spread to other epitopes. The similarity and cross-reactivity between the initial targets of nRNP and Sm autoantibodies identifies a likely commonality in cause and a focal point for intermolecular epitope spreading.[67]
Others
Elevated expression of HMGB1 was found in the sera of people and mice with systemic lupus erythematosus, high mobility group box 1 (HMGB1) is a nuclear protein participating in chromatin architecture and transcriptional regulation. Recently, there is increasing evidence HMGB1 contributes to the pathogenesis of chronic inflammatory and autoimmune diseases due to its inflammatory and immune stimulating properties.[68]
Diagnosis
The cause of SLE is not clear.[1] It is thought to involve genetics together with environmental factors.[4] Among identical twins, if one is affected there is a 24% chance the other one will be as well.[1] Female sex hormones, sunlight, smoking, vitamin D deficiency, and certain infections, are also believed to increase the risk.[4] The mechanism involves an immune response by autoantibodies against a person's own tissues.[1] These are most commonly anti-nuclear antibodies and they result in inflammation.[1] Diagnosis can be difficult and is based on a combination of symptoms and laboratory tests.[1] There are a number of other kinds of lupus erythematosus including discoid lupus erythematosus, neonatal lupus, and subacute cutaneous lupus erythematosus.[1]
There is no cure for SLE.[1] Treatments may include NSAIDs, corticosteroids, immunosuppressants, hydroxychloroquine, and methotrexate.[1] Alternative medicine has not been shown to affect the disease.[1] Life expectancy is lower among people with SLE.[5] SLE significantly increases the risk of cardiovascular disease with this being the most common cause of death.[4] With modern treatment about 80% of those affected survive more than 15 years.[3] Women with lupus have pregnancies that are higher risk but are mostly successful.[1]
Rate of SLE varies between countries from 20 to 70 per 100,000.[2] Women of childbearing age are affected about nine times more often than men.[4] While it most commonly begins between the ages of 15 and 45, a wide range of ages can be affected.[1][2] Those of African, Caribbean, and Chinese descent are at higher risk than white people.[4][2] Rates of disease in the developing world are unclear.[6] Lupus is Latin for "wolf": the disease was so-named in the 13th century as the rash was thought to appear like a wolf's bite
SLE is one of several diseases known as "the great imitator" because it often mimics or is mistaken for other illnesses.[9] SLE is a classical item in differential diagnosis,[10] because SLE symptoms vary widely and come and go unpredictably. Diagnosis can thus be elusive, with some people having unexplained symptoms of SLE for years.
Common initial and chronic complaints include fever, malaise, joint pains, muscle pains, and fatigue. Because these symptoms are so often seen in association with other diseases, these signs and symptoms are not part of the diagnostic criteria for SLE. When occurring in conjunction with other signs and symptoms, however, they are considered suggestive.[11]
While SLE can occur in both males and females, it is found far more often in women, and the symptoms associated with each sex are different.[5] Females tend to have a greater number of relapses, a low white blood cell count, more arthritis, Raynaud's phenomenon, and psychiatric symptoms. Males tend to have more seizures, kidney disease, serositis (inflammation of tissues lining the lungs and heart), skin problems, and peripheral neuropathy.[12]
Skin
As many as 70% of people with lupus have some skin symptoms. The three main categories of lesions are chronic cutaneous (discoid) lupus, subacute cutaneous lupus, and acute cutaneous lupus. People with discoid lupus may exhibit thick, red scaly patches on the skin. Similarly, subacute cutaneous lupus manifests as red, scaly patches of skin but with distinct edges. Acute cutaneous lupus manifests as a rash. Some have the classic malar rash (or butterfly rash) associated with the disease.[13] This rash occurs in 30 to 60% of people with SLE.[14]
Hair loss, mouth and nasal ulcers, and lesions on the skin are other possible manifestations.[15]
Muscles and bones
The most commonly sought medical attention is for joint pain, with the small joints of the hand and wrist usually affected, although all joints are at risk. More than 90 percent of those affected will experience joint or muscle pain at some time during the course of their illness.[16] Unlike rheumatoid arthritis, lupus arthritis is less disabling and usually does not cause severe destruction of the joints. Fewer than ten percent of people with lupus arthritis will develop deformities of the hands and feet.[16] People with SLE are at particular risk of developing osteoarticular tuberculosis.[17]
A possible association between rheumatoid arthritis and SLE has been suggested,[18] and SLE may be associated with an increased risk of bone fractures in relatively young women.[19]
Blood
Anemia is common in children with SLE[20] and develops in about 50% of cases.[21] Low platelet and white blood cell counts may be due to the disease or a side effect of pharmacological treatment. People with SLE may have an association with antiphospholipid antibody syndrome[22] (a thrombotic disorder), wherein autoantibodies to phospholipids are present in their serum. Abnormalities associated with antiphospholipid antibody syndrome include a paradoxical prolonged partial thromboplastin time (which usually occurs in hemorrhagic disorders) and a positive test for antiphospholipid antibodies; the combination of such findings have earned the term "lupus anticoagulant-positive". Another autoantibody finding in SLE is the anti-cardiolipin antibody, which can cause a false positive test for syphilis.[citation needed]
Heart
SLE may cause pericarditis—inflammation of the outer lining surrounding the heart, myocarditis—inflammation of the heart muscle, or endocarditis—inflammation of the inner lining of the heart. The endocarditis of SLE is non-infectious, and is also called (Libman–Sacks endocarditis). It involves either the mitral valve or the tricuspid valve. Atherosclerosis also occurs more often and advances more rapidly than in the general population.[23][24]
Lungs
SLE can cause pleuritic pain as well as inflammation of the pleurae known as pleurisy, which can rarely give rise to shrinking lung syndrome involving a reduced lung volume.[25][26] Other associated lung conditions include pneumonitis, chronic diffuse interstitial lung disease, pulmonary hypertension, pulmonary emboli, and pulmonary hemorrhage.
Kidneys
Painless passage of blood or protein in the urine may often be the only presenting sign of kidney involvement. Acute or chronic renal impairment may develop with lupus nephritis, leading to acute or end-stage kidney failure. Because of early recognition and management of SLE, end-stage renal failure occurs in less than 5%[27][28] of cases; except in the black population, where the risk is many times higher.
The histological hallmark of SLE is membranous glomerulonephritis with "wire loop" abnormalities.[29] This finding is due to immune complex deposition along the glomerular basement membrane, leading to a typical granular appearance in immunofluorescence testing.
Neuropsychiatric
Further information: Neuropsychiatric systemic lupus erythematosus
Neuropsychiatric syndromes can result when SLE affects the central or peripheral nervous system. The American College of Rheumatology defines 19 neuropsychiatric syndromes in systemic lupus erythematosus.[30] The diagnosis of neuropsychiatric syndromes concurrent with SLE (now termed as NPSLE),[31] is one of the most difficult challenges in medicine, because it can involve so many different patterns of symptoms, some of which may be mistaken for signs of infectious disease or stroke.[32]
A common neurological disorder people with SLE have is headache,[33] although the existence of a specific lupus headache and the optimal approach to headache in SLE cases remains controversial.[34] Other common neuropsychiatric manifestations of SLE include cognitive dysfunction, mood disorder, cerebrovascular disease,[33] seizures, polyneuropathy,[33] anxiety disorder, psychosis, depression, and in some extreme cases, personality disorders.[35] Steroid psychosis can also occur as a result of treating the disease.[31] It can rarely present with intracranial hypertension syndrome, characterized by an elevated intracranial pressure, papilledema, and headache with occasional abducens nerve paresis, absence of a space-occupying lesion or ventricular enlargement, and normal cerebrospinal fluid chemical and hematological constituents.[36]
More rare manifestations are acute confusional state, Guillain–Barré syndrome, aseptic meningitis, autonomic disorder, demyelinating syndrome, mononeuropathy (which might manifest as mononeuritis multiplex), movement disorder (more specifically, chorea), myasthenia gravis, myelopathy, cranial neuropathy and plexopathy.
Neurological disorders contribute to a significant percentage of morbidity and mortality in people with lupus.[37] As a result, the neural side of lupus is being studied in hopes of reducing morbidity and mortality rates.[30] One aspect of this disease is severe damage to the epithelial cells of the blood–brain barrier. In certain regions, depression affects up to 60% of women with SLE.[38]
Eyes
Eye involvement is seen in up to one-third of people. The most common diseases are dry eye syndrome and secondary Sjögren's syndrome, but episcleritis, scleritis, retinopathy (more often affecting both eyes than one), ischemic optic neuropathy, retinal detachment, and secondary angle-closure glaucoma may occur. In addition, the medications used to treat SLE can cause eye disease: long-term glucocorticoid use can cause cataracts and secondary open-angle glaucoma, and long-term hydroxychloroquine treatment can cause vortex keratopathy and maculopathy.[39]
Reproductive
Further information: Systemic lupus erythematosus and pregnancy
SLE causes an increased rate of fetal death in utero and spontaneous abortion (miscarriage). The overall live-birth rate in people with SLE has been estimated to be 72%.[40] Pregnancy outcome appears to be worse in people with SLE whose disease flares up during pregnancy.[41]
Neonatal lupus is the occurrence of SLE symptoms in an infant born from a mother with SLE, most commonly presenting with a rash resembling discoid lupus erythematosus, and sometimes with systemic abnormalities such as heart block or enlargement of the liver and spleen.[42] Neonatal lupus is usually benign and self-limited.[42]
Systemic
Fatigue in SLE is probably multifactorial and has been related to not only disease activity or complications such as anemia or hypothyroidism, but also to pain, depression, poor sleep quality, poor physical fitness and lack of social support.[43][44]
Causes
SLE is presumably caused by a genetic susceptibility coupled with an environmental trigger which results in defects in the immune system. One of the factors associated with SLE is vitamin D deficiency.[45]
Genetics
SLE does run in families, but no single causal gene has been identified. Instead, multiple genes appear to influence a person's chance of developing lupus when triggered by environmental factors. HLA class I, class II, and class III genes are associated with SLE, but only classes I and II contribute independently to increased risk of SLE.[46] Other genes which contain risk variants for SLE are IRF5, PTPN22, STAT4,[47] CDKN1A,[48] ITGAM, BLK,[47] TNFSF4 and BANK1.[49] Some of the susceptibility genes may be population specific.[47] Genetic studies of the rates of disease in families supports the genetic basis of this disease with a heritability of >66%.[50] Identical (monozygotic) twins were found to share susceptibility to the disease at >35% rate compared to fraternal (dizygotic) twins and other full siblings who only showed a 2–5% concordance in shared inheritance.[50]
Since SLE is associated with many genetic regions, it is likely an oligogenic trait, meaning that there are several genes that control susceptibility to the disease.[51]
SLE is regarded as a prototype disease due to the significant overlap in its symptoms with other autoimmune diseases.[52]
Drug reactions
Drug-induced lupus erythematosus is a (generally) reversible condition that usually occurs in people being treated for a long-term illness. Drug-induced lupus mimics SLE. However, symptoms of drug-induced lupus generally disappear once the medication that triggered the episode is stopped. More than 38 medications can cause this condition, the most common of which are procainamide, isoniazid, hydralazine, quinidine, and phenytoin.[53][10]
Non-systemic forms of lupus
Discoid (cutaneous) lupus is limited to skin symptoms and is diagnosed by biopsy of rash on the face, neck, scalp or arms. Approximately 5% of people with DLE progress to SLE.[54]
Pathophysiology
SLE is triggered by environmental factors that are unknown. In SLE, the body's immune system produces antibodies against itself, particularly against proteins in the cell nucleus. These antibody attacks are the immediate cause of SLE.[10][55][56]
SLE is a chronic inflammatory disease believed to be a type III hypersensitivity response with potential type II involvement.[57] Reticulate and stellate acral pigmentation should be considered a possible manifestation of SLE and high titers of anti-cardiolipin antibodies, or a consequence of therapy.[58]
People with SLE have intense polyclonal B-cell activation, with a population shift towards immature B cells. Memory B cells with increased CD27+/IgD—are less susceptible to immunosuppression. CD27-/IgD- memory B cells are associated with increased disease activity and renal lupus. T cells, which regulate B-cell responses and infiltrate target tissues, have defects in signaling, adhesion, co-stimulation, gene transcription, and alternative splicing. The cytokines B-lymphocyte stimulator (BLys), interleukin 6, interleukin 17, interleukin 18, type I interferons, and tumor necrosis factor α (TNFα) are involved in the inflammatory process and are potential therapeutic targets.[4][59][60]
In the complement system low C3 levels are associated with systemic lupus erythematosus[61]
Cell death signaling
Apoptosis is increased in monocytes and keratinocytes
Expression of Fas by B cells and T cells is increased
There are correlations between the apoptotic rates of lymphocytes and disease activity.
Necrosis is increased in T lymphocytes.
Tingible body macrophages (TBMs) – large phagocytic cells in the germinal centers of secondary lymph nodes – express CD68 protein. These cells normally engulf B cells that have undergone apoptosis after somatic hypermutation. In some people with SLE, significantly fewer TBMs can be found, and these cells rarely contain material from apoptotic B cells. Also, uningested apoptotic nuclei can be found outside of TBMs. This material may present a threat to the tolerization of B cells and T cells. Dendritic cells in the germinal center may endocytose such antigenic material and present it to T cells, activating them. Also, apoptotic chromatin and nuclei may attach to the surfaces of follicular dendritic cells and make this material available for activating other B cells that may have randomly acquired self-specificity through somatic hypermutation.[62] Necrosis, a pro-inflammatory form of cell death, is increased in T lymphocytes, due to mitochondrial dysfunction, oxidative stress, and depletion of ATP.[63]
Clearance deficiency
Impaired clearance of dying cells is a potential pathway for the development of this systemic autoimmune disease. This includes deficient phagocytic activity and scant serum components in addition to increased apoptosis.
SLE is associated with defects in apoptotic clearance, and the damaging effects caused by apoptotic debris. Early apoptotic cells express “eat-me” signals, of cell-surface proteins such as phosphatidylserine, that prompt immune cells to engulf them. Apoptotic cells also express “find-me” signals, to attract macrophages and dendritic cells. When apoptotic material is not removed correctly by phagocytes, they are captured instead by antigen-presenting cells, which leads to development of antinuclear antibodies.[4]
Monocytes isolated from whole blood of people with SLE show reduced expression of CD44 surface molecules involved in the uptake of apoptotic cells. Most of the monocytes and tingible body macrophages (TBMs), which are found in the germinal centres of lymph nodes, even show a definitely different morphology; they are smaller or scarce and die earlier. Serum components like complement factors, CRP, and some glycoproteins are, furthermore, decisively important for an efficiently operating phagocytosis. With SLE, these components are often missing, diminished, or inefficient.
Recent research has found an association between certain people with lupus (especially those with lupus nephritis) and an impairment in degrading neutrophil extracellular traps (NETs). These were due to DNAse1 inhibiting factors, or NET protecting factors in people's serum, rather than abnormalities in the DNAse1 itself.[64] DNAse1 mutations in lupus have so far only been found in some Japanese cohorts.[65]
The clearance of early apoptotic cells is an important function in multicellular organisms. It leads to a progression of the apoptosis process and finally to secondary necrosis of the cells if this ability is disturbed. Necrotic cells release nuclear fragments as potential autoantigens, as well as internal danger signals, inducing maturation of dendritic cells (DCs), since they have lost their membranes' integrity. Increased appearance of apoptotic cells also stimulates inefficient clearance. That leads to maturation of DCs and also to the presentation of intracellular antigens of late apoptotic or secondary necrotic cells, via MHC molecules. Autoimmunity possibly results by the extended exposure to nuclear and intracellular autoantigens derived from late apoptotic and secondary necrotic cells. B and T cell tolerance for apoptotic cells is abrogated, and the lymphocytes get activated by these autoantigens; inflammation and the production of autoantibodies by plasma cells is initiated. A clearance deficiency in the skin for apoptotic cells has also been observed in people with cutaneous lupus erythematosus (CLE).[66]
Germinal centers
In healthy conditions, apoptotic lymphocytes are removed in germinal centers (GC) by specialized phagocytes, the tingible body macrophages (TBM), which is why no free apoptotic and potential autoantigenic material can be seen. In some people with SLE, build up of apoptotic debris can be observed in GC because of an ineffective clearance of apoptotic cells. In close proximity to TBM, follicular dendritic cells (FDC) are localised in GC, which attach antigen material to their surface and, in contrast to bone marrow-derived DC, neither take it up nor present it via MHC molecules.
Autoreactive B cells can accidentally emerge during somatic hypermutation and migrate into the germinal center light zone. Autoreactive B cells, maturated coincidentally, normally do not receive survival signals by antigen planted on follicular dendritic cells and perish by apoptosis. In the case of clearance deficiency, apoptotic nuclear debris accumulates in the light zone of GC and gets attached to FDC. This serves as a germinal centre survival signal for autoreactive B-cells. After migration into the mantle zone, autoreactive B cells require further survival signals from autoreactive helper T cells, which promote the maturation of autoantibody-producing plasma cells and B memory cells. In the presence of autoreactive T cells, a chronic autoimmune disease may be the consequence.
Anti-nRNP autoimmunity
Anti-nRNP autoantibodies to nRNP A and nRNP C initially targeted restricted, proline-rich motifs. Antibody binding subsequently spread to other epitopes. The similarity and cross-reactivity between the initial targets of nRNP and Sm autoantibodies identifies a likely commonality in cause and a focal point for intermolecular epitope spreading.[67]
Others
Elevated expression of HMGB1 was found in the sera of people and mice with systemic lupus erythematosus, high mobility group box 1 (HMGB1) is a nuclear protein participating in chromatin architecture and transcriptional regulation. Recently, there is increasing evidence HMGB1 contributes to the pathogenesis of chronic inflammatory and autoimmune diseases due to its inflammatory and immune stimulating properties.[68]
Diagnosis
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