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

Cord blood and fetal liver B cells were immortalized using Epstein Barr virus, and IgM antibodies from the resulting 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 I 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 self-antigens. In cord blood clones, 16 out of 26 bound lo auto-antigens. Many of the clones reacted with more than one auto-antigen and were 'polyreactive'. 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'. [ABSTRACT FROM AUTHOR]