Scand. J. Immunol. 31, 33-43. 1990 The Antibody Repertoire of Early Human B Cells I. High Frequency of Autoreactivity and Polyreactivity P, M. LYDYARD. R. QUARTEY-PAPAFIO, B. BROKER, L. MACKENZIE, J. JOUQUAN, M. A, BLASCHEK, J. STEELE, M, PETROU, P. COLLINS, D. ISENBHRG & P, Y. YOUINOU Departments of Immunology. Rheumatology, and Obstetrics and Gynaecology, University College and Middlesex School of Medicine, London. UK; and Department oflmmunology. University of Brest, France Lydyard, P.M,. Quartey-Papafio. R,, Broker, B,, Mackenzie, L,, Jouquati, J,, Blaschek, M,A,. Steele. J,. Petrou, M,. Collins. P,. Isenberg, D, & Youinou, P,Y, The Antibody Repertoire of Early Human B Cel Is. I, High Frequency ol'Autoreactivity and Polyreactivity, Scand. J. Immwml. 31,33-43, 1990 Cord blood and fetal liver B cells were immortalized using Epsleln Barr virus, and IgM antibodies from theresullinglinesandclones were examined for their binding to a variety of auto- antigens and micro-organisms by ELISA and fluorescence assays. Auto-antigens lested included Fc of IgG, ssDNA and dsDNA, cardiolipin. histories 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 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 ( > SQ"A. ) and felal liver ( > 70"'!i) argues for many of these ciones 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 micro- organisms. These IgM antibodies are similar to those described by others as 'natural antibodies', P. M. Lydyard. PhD, Department of Immunology, V.C.M.S.M.. Arthur Stanley House. 40-50. Tottenham Street, London WIP 9PG. UK It is now well documented that normal indi- viduals possess autoreactive B cells [4. 24] which can be induced to secrete auto-antibodies in vitro [8. 30], A number of studies have indicated that the frequency of a subset of B cells carrying the 67-kDa CD5 molecule is elevated in RA [25. 31] and Sjogren's patients [5. 32] and. furthermore. that these cells are responsible for the majority of anti-DNA and anti-Pc auto-antibodies produced by B cells in autoimmune mouse models [12. 28] and in normal adult blood [3, 11], Cord blood B cells have been shown to produce both of tbcse auto-antibodies following polyclonal activation in vitro (Ref, 18, and our unpublished observa- tion) and are enriched In the CD5 ' subset (Ref, 10, and our unpublished observation). In order to analyse the autoreactivity reper- toires of cord blood and fetal liver B cells at the cellular level we used the polyclonal B-cell acti- vator Fpstein-Barr virus (FBV) to produce lines/ clones [30], Our data indicate that the majority of EBV- driven cord and fetal B cells secrete IgM anti- bodies which react with at least one of our tested auto-antigens. Many reacted with several auto- antigens and with some micro-organisms. MATERIALS AND METHODS Preparation of cells. Umbilical cord blood from seven full-lerm donors and liver cells from a 22-week-old fetus were used in this study. Cord blood mononuclear cells were prepared from the blood by centrifugation over Ficoll-Hypaque (F/H) gradients as previously de- 33