In fact, one of the first autoimmune complications to be described in primary immune deficiency was the rheumatological disease that occurs in XLA [7]. While subjects with the hyper-IgM syndromes have recurrent opportunistic infections with Pneumocystis jiroveci and Cryptosporidium and for the X-linked version, a tendency to develop biliary tract disease [8,9], autoimmune complications are also common. These occur in both the X-linked and autosomal RG 7204 forms and include joint, bowel, liver and haematological disease. Table 2 outlines the most common autoimmune conditions in groups of subjects with the X-linked and the autosomal form of hyper-IgM syndrome due to mutations in the activation-induced

cytidine deaminase gene (AID). Characteristics of these defects are the development of IgM antibodies but not IgG or IgA, lack of response to T dependent antigens and an inability to develop memory B cells. For the X-linked form, loss of CD40L signals on dendritic cells and thymic epithelial cells also occurs, and potentially a loss of development of Tregs. Some or all of these molecular defects leads to an increased number of mature naive B cells, which express a high proportion of autoreactive antibodies. As for subjects with XLA, subjects with hyper-IgM syndromes have circulating B cells with autoimmune potential;

however, these are not new emigrant B cells but naive B cells, suggesting loss of peripheral tolerance. Alterations ABT-263 chemical structure in B cell receptor signalling pathways are also found in patients with defects in Toll-like receptor (TLR) signalling, such as interleukin-1 receptor-associated kinase 4 (IRAK-4), myeloid differentiation primary response gene 88 (MyD88) and unc-93 homologue B1 (UNC-93B) [10–12] for less clear reasons.

These observations demonstrate Molecular motor that B cell tolerance in humans normally relies upon a number of pathways working as an interactive network to exclude B cell autoimmunity. In CVID, B cells secrete immune globulins poorly, and fail to differentiate into plasma cells. About 25–30% of these subjects develop autoimmune complications; for unclear reasons, more than 50% of these involve the haematological system, with immune thrombocytopenia and haemolytic anaemia being foremost [13–17] (Table 3). While defects of single genes have helped to elucidate autoimmunity in selected primary immune defects, the cause of autoimmunity in CVID has proved more complex and a number of mechanisms are likely. Similar to the hyper-IgM syndrome, CVID B cells exhibit impaired somatic hypermutation [18], and there are reduced numbers of CD27+ memory B cells and an even greater losses of isotype-switched (IgD– IgM– CD27+) memory B cells [19]. Loss of these cells is associated with both the development of autoimmunity, lymphoid hyperplasia, splenomegaly and granulomatous disease [19–22] (Fig. 1 shows data for a Mount Sinai cohort).