Characterization and V-H sequences of human monoclonal anti-F(ab ')(2) autoantibodies from normals and Sjogren's syndrome patients

To investigate the genetic background of anti-F(ab')(2) autoantibodies and the mechanism behind their production we have analyzed 10 human monoclonal antibodies directed against IgG F(ab')(2) and IgG Feb. They were all derive d from peripheral blood by the EBV/hybridoma technique. Eight were from thr ee healthy individuals and two from two patients with primary Sjogren's syn drome (pSS). They react with epitopes on distinct regions of IgG, including epitopes present on or near the hinge of IgG, epitopes on the Fd gamma, an d an antigenic determinant(s) present on lambda light chains. These determi nants are either exposed on the intact IgG molecule or revealed following p epsin or papain digestion. The V-H germline gene repertoire used is diverse and with considerable overlap with that used by rheumatoid factors (RF). T he two IgG antibodies from normals are extensively mutated (13 and 24 mutat ions/V-H), but with a replacement to silent mutation ratio in the CDR(H)1 2 of only 3.7. The IgM antibodies from normals are also heavily mutated (m ean 10 mutations/V-H). This suggests that anti-F(ab')(2) from normals are g enerated by an antigen-driven somatic hypermutation mechanism. In contrast, the two IgM antibodies from pSS are virtually unmutated in both V-H and V- L. Together with published data of pSS RF and anti-ao 52-kDa sequences (1-3 ), this suggests that there is an expanded population of naive B cells with autoantibody specificities in the peripheral blood of pSS patients. (C) 20 00 Academic Press.