[B lymphocyte differentiation in granulomatous tissues of the lung and the nasal mucosa in Wegener's granulomatosis: origin of anti-neutrophil cytoplasmic antibody formation?]

Abstract

Wegener's granulomatosis (WG) starts with granulomatous inflammation of the respiratory tract before it converts into a potentially organ and life threatening systemic vasculitis associated with anti-neutrophil cytoplasmic antibodies (ANCA). The site of formation of the highly specific ANCA directed against "Wegener's autoantigen" proteinase 3 (PR3) is still unknown. Previously, we have shown that follicle-like B lymphocytic infiltrates in the vicinity to PR3 expressing cells in WG-granulomata. We characterized the immunoglobulin-VH repertoire in lung and nasal granulomata (paraffin embedded) from four WG patients. A total of 115 individual VH genes were characterized and compared to 84 VH genes from the peripheral blood of a healthy donor. We found an increased frequency of mutations with a bias to amino acid exchanges within the antigen binding sites (CDR) 1 and 2 in WG tissue. A large number of mutations led to negatively charged amino acids and may increase affinity to the positively charged PR3. Furthermore, the occurrence of differently mutated members of one B cell clone indicates clonal expansion and intraclonal diversification by an antigen, e.g. PR3. Several WG tissue derived genes displayed similarities to published sequences from peripheral PR3 ANCA producing B cells. Thus, granulomata of the lower and upper respiratory tract contain follicle-like B cell clusters with a selected VH repertoire infiltrate in WG. WG granulomata could be the place of autoantigen presentation and formation of high-affinity ANCA within neoformed ectopic or tertiary lymphoid-like tissue areas.