Deficiencies of an early component of the classical complement pathway (C1q, C1r, C1s, C2, C4) have been associated with lupus like autoimmune conditions. The reason for this is that these proteins help to clean up large groups of molecules called immune complexes before they can cause inflammation. Dead cells are also removed by these complement molecules. Without these proteins, immune complexes and dead cells are not removed and cause local irritation.
In HAE types I and II, complement proteins C2 and C4 are low. However, HAE patients have been shown to have a normal level of immune complexes. For this reason, it is still unclear whether or not low C2 and C4 may contribute to overall inflammation and pain profile for these patients. Despite this fact, it is still possible that deficiency in C2 and C4 may predispose HAE patients to autoimmune diseases.
A number of studies have assessed the prevalence of autoimmune conditions in HAE patients. One study looked specifically for two thyroid antibodies and found that 13.2% HAE patients had autoantibodies to the thyroid.
When expanding the autoimmune profile to include “lupus-like” conditions such as those often associated with complement deficiencies, a much higher prevalence of autoantibodies was found in HAE patients. Three other studies measured the frequency of ANA (anti-nuclear antibody, a generic marker found in many autoimmune conditions); RF (Rheumatoid Factor, associated with rheumatoid arthritis); anti-thyroglobulin(autoimmune thyroiditis); TPO (thyroid peroxidase, autoimmune thyroiditis); and thyroid antibodies along with some or all of the following antibodies: anti-dsDNA (anti double stranded DNA, systemic lupus erythematosus); ENA (extractable nuclear antigens, a panel of six tests that can identify mixed connective tissue disease, systemic lupus erythematosus, Sjogren’s, Scleroderma and dermatomyositis); TMA (microsomal antibodies, autoimmune thyroiditis); AMA (antimitochondrial antibodies, drug-induced or systemic lupus erythematosus, Sjogren’s, autoimmune hemolytic anemia, autoimmune liver disease); ANCA (antineutrophil cytoplasmic antibodies); anti-cardiolipin (systemic lupus erythematosus, Behcet’s, antiphospholipid syndrome); anti-b2GPI (b2-glycoprotein I, systemic lupus erythematosus, Behcet’s, antiphospholipid syndrome); anti-C1q (urticarial vasculitis); anti-P ribosomal (systemic lupus erythmatosis); EMA (anti-endomysial antibodies, Celiac disease); tTG (anti-tissue transglutaminase antibodies, dermatitis herpetiformis); and ASCA (anti-saccharomyces cerevisiae antibodies, Behcet’s, Celiac disease, Crohn’s disease, ulcerative colitis). The three studies found that 47.5-48% HAE patients had at least one of these autoantibodies. In comparison, the average for healthy controls was 10%.
Other studies looked at prevalence of autoimmune disease rather than autoantibodies. One study found that 12% of HAE patients had at one of the following autoimmune conditions: glomerulonephritis, Sjogren’s syndrome, irritable bowel disease, thyroiditis, systemic lupus erythematosus, rheumatoid arthritis, drug induced lupus, pernicious anemia, juvenile RA with IgA deficiency, or sicca syndrome.
Other studies found that 3.4% HAE patients had lupus rash or glomerulonephritis; that 0.9% had RA or Sjogren’s; that 11.5% had Crohn’s, Celiac, Hashimoto’s thyroiditis, discoid lupus erythematosus, chronic lymphocytic leukemia, MGUS, or IgA deficiency; that 11.4% had systemic lupus erythematosus, Celiac, multiple sclerosis-like syndrome, systemic sclerosis, or mixed connective tissue disease; that 4.2% had lupus like syndrome, psoriatic arthritis, mixed connective tissue disease or antiphospholipid syndrome; that 0.4-0.9% had lupus-like or unspecific cutaneous lupus or subacute lupus.
An interesting feature of HAE is the frequent complaint of decreased sense of smell. Facial edema and chronic rhinosinusitis were not found to be the cause. However, systemic lupus erythematosus and Sjogren’s syndrome can also cause impairment of smell. Despite the frequency of lupus in HAE patients, it usually affected the mucocutaneous regions of the body and was generally mild.
In addition to the frequent prevalence of autoantibodies and autoimmune disease, HAE patients have increased B cell activation and autoreactive B cells. This can also contribute to an inflammatory and autoimmune profile.
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