SUMMARY: Human monoclonal antibodies (Mabs) against the O antigens of lipopolysaccharides (LPS) were produced by cell fusion between human tonsillar lymphocytes and P3-X63-Ag8-U1 (P3U1) mouse myeloma cells. To obtain human Mabs efficiently, 6d culture supernatants of pokeweed-mitogen-stimulated lymphocytes (21 cultures from peripheral blood and 76 from tonsils) were assayed by ELISA. Five tonsillar lymphocytes which produced IgG antibody specific for LPS were preselected for fusion. The human Mabs, named P1-1 (IgG2, λ), P5-1 (IgG2, λ), P7-1 (IgG2, λ), P8-1 (IgG2, λ) and P10-1 (IgG2, λ), bound with high specificity to Homma standard serotype strains A, E, B, G and I, respectively, and recognized O antigens. Each Mab showed opsonophagocytic killing activity of the corresponding serotype strain. Four of the Mabs caused agglutination at a very low concentration; a rather higher concentration of P7-1 was required for this effect. Although all the Mabs conferred type-specific protection against peritoneal infection, the strongly agglutinating Mabs provided better protection than the moderately agglutinating P7-1. The protective activity of P8-1 was estimated in compromised mice. A low dose (PD 0.5-0.6 μg per mouse) of P8-1 prevented subcutaneous infection in burned mice and peritoneal infection in leucopenic mice. All the hybridomas described here could be cultured in serum-free medium, and they have continued to secrete human Mabs for more than 14 months at rates of 10-20 μg per 10 cells in 24 h. These results suggested that these five human Mabs specific for O antigens might be useful in the prophylaxis and treatment of infections.


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