The autoreactivity of B cells in hereditary angioedema due to C1 inhibitor deficiency

Summary Patients with hereditary angioedema (HAE) tend to produce autoantibodies and have a propensity to develop immunoregulatory disorders. We characterize the profile of autoantibodies in a group of HAE patients and investigate their memory B cells' phenotype and activation status. We studied the activity status phenotype, Toll‐like receptor (TLR)‐9 expression and total phosphotyrosine in B cells isolated from HAE patients. Additionally, the following autoantibodies were assessed in the serum of 61 HAE patients: anti‐nuclear, rheumatoid factor, anti‐cardiolipin, anti‐tissue transglutaminase, anti‐endomysial, anti‐Saccharomyces cerevisiae, anti‐thyroid and anti‐neutrophil cytoplasmic antibodies. In 47·5% of HAE patients we detected at least one of the tested autoantibodies. Expression of CD69, CD5 and CD21 was found to be significantly higher on memory B cells from HAE patients compared to healthy controls (4·59 ± 4·41 versus 2·06 ± 1·81, P = 0·04, 8·22 ± 7·17 versus 3·65 ± 3·78, P = 0·05, 2·43 ± 0·54 versus 1·92 ± 0·41, P = 0·01, respectively). Total phosphotyrosine in B cells from HAE patients was significantly higher compared to healthy controls (4·8 ± 1·1 versus 2·7 ± 1·3, P = 0·0003). Memory B cells isolated from the HAE group contained higher amounts of TLR‐9 compared to healthy controls (8·17 ± 4·1 versus 4·56 ± 1·6, P = 0·0027). Furthermore, the expression of TLR‐9 in memory B cells from HAE patients with autoantibodies was significantly higher than the control group (10 ± 4·7 versus 4·56 ± 1·6, P = 0·0002) and from that in HAE patients without autoantibodies (10 ± 4·7 versus 5·8 ± 0·9, P = 0·036). HAE patients have enhanced production of autoantibodies due most probably to the increased activation of B cells, which was found to be in association with a high expression of TLR‐9.