The Antibody Repertoire of Early Human B Cells I. High Frequency of Autoreactivity and Polyreactivity

antibodies from theresulting lines and clones were examined for their binding to a variety of auto-antigens and micro-organisms by ELISA and fluorescence assays. Auto-antigens tested included Fc of IgG, ssDNA and dsDNA, cardiolipin, histones 1-4, collagens type I and II. thyroglobulin, cytoskeletal components, and a tissue section screen. Of 71 cell lines tested, all but 19 showed some autoreactivity. All 32 fetal liver lines reacted to some seif-antigens. In cord blood clones, 16 out of 26 bound to auto-antigens. Many of the clones reacted with more than one auto-antigen and were ‘polyrcactive’. Some of the cord blood clones bound to extracts of micro-organisms, showing specificity for both endogenous and exogenous antigens. The high frequency of CD5+ B cells in the cord blood (> 50%) and fetal liver (> 70%) argues for many of these clones being derived from this subset. Therefore, our data support the concept that many ‘early’ B cells produce polyreactive IgM which can bind to a variety of different auto-antigens and microorganisms. These IgM antibodies are similar to those described by others as ‘natural antibodies’.