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Peripheral blood lymphocytes from meningitis patients and healthy meningococcal carriers were fused by electrofusion with the three human-murine heteromyeloma cell lines CB-F7, K6H6B5 and H7NS. 934 hybridomas producing human immunoglobulins were obtained in 30 fusions. Heteromyeloma K6H6B5 yielded a significantly higher proportion of hybridomas producing IgG antibodies than did the two other cell lines. CB-F7 and K6H6B5 yielded comparable numbers of hybridomas whose supernatants reacted with homologous bacteria, whereas the cell line H7NS was less efficient.

To study the human fetal B cell repertoire, liver and spleen lymphocytes were fused with the human x mouse heteromyeloma line CB-F7. Initially, 2310 IgM and 181 IgG producing hybridoma lines were established. Culture supernatants were analysed for binding activity to antigens from both the exogeneous and the endogeneous environments. For IgG secreting cell lines no antigenetic specificity has been detected. However, independently from the gestational age, monoclonal IgM antibodies binding to bacterial antigens (tetanus toxoid, lipid A, N. meningitidis antigens) were found. In particular, nearly 10% of the hybridomas obtained from fetal liver produced antibodies binding to lipid A (endotoxin). Among the IgM antibodies with anti-bacterial specificities approximately 30% were found to be polyspecific, i.e. these antibodies recognized auto-antigens of different molecular origin as well (ssDNA, keratin, myosin, actin). We conclude that polyreactive natural IgM antibodies may be generated during fetal life, which may take part in the formation of a humoral anti-infectious first line defense barrier in the neonate.