Human T-T hybridomas were established by fusion of concanavalin A-activated OKT-4+ T cells with hypoxanthine guanine phosphoribosyl transferase-deficient as well as nondeficient T cell lines. Four hybrids were selected for further study. Supernatant from hybrid clone J1.3 specifically enhanced IgA production and secretion by isolated human B cells, with increases in IgA plaque-forming cells approaching those seen with addition of autologous T cells and pokeweed mitogen. A monoclonal lymphocytic leukemia with membrane IgA also differentiated to IgA plasma cells by this supernatant. Evidence suggests that this hybrid supernatant acts on post-switch IgA-committed B cells. The other hybrids were not isotype specific; hybrid J2S1 enhanced polyclonal Ig secretion and hybrids K1 and K8 induced B cell proliferation without induction of Ig secretion.

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