VH/VL gene expression in polyreactive-antibody-producing human hybridomas from the fetal B cell repertoire.

Among a panel of nearly 3,000 IgM-producing hybridomas obtained from 22 independent fusions of human fetal lymphocytes (liver/spleen; 15th-36th gestational week) a high number (5-10%) produced autoantibodies, independently of the gestational age. A significant portion of these autoantibodies was found to be polyreactive, i.e. capable of binding to more than two antigens, when tested against a set of five antigens of the internal (ssDNA, thrombocytes, keratin) and external (lipid A, tetanus toxoid) environment. Analyzing the IgVH genes utilized in eight polyreactive and two putatively nonpolyreactive hybridomas, members of the VHI, III, IV and VI families were found once, seven times, once and once, respectively, mostly with germline identity. All but one of the utilized gene elements could be related to the biased VH gene repertoire said to be expressed during the early ontogeny of the human immune system. We also noted a bias for the utilization of DN1 (3/10), DHQ52 (3/10), JH2 (4/10) and JH6 (4/10) elements, whereas all heavy-chain CDR3 regions manifest a diversity by addition of N nucleotides and/or exonuclease activity on coding segments. In addition, VL segments which belong to different subgroups of both isotypes were found to be used. The molecular basis of polyreactive immunoglobulin specificities in human fetuses is discussed.