Characterization of human CD4+ T-cell clones that secrete helper factor(s) for B-cell proliferation and maturation

Human peripheral blood lymphocytes (PBL) were activated with K46M, a m mitogenic monoclonal antibody against La-reactive T lymphocyte surface structures. The cultures were expanded in the presence of interleukin 2 (IL-2). After 1 month of culture, the activated T cells were cloned by limiting dilution at 0.5 cells/well. Five clones with the CD3+CD4+ phenotype and one clone with the CD3+CD8+ phenotype were obtained. The CD3+CD8+ clone (K99) displayed a strong major histocompatibility complex (MHC)-unrestricted cytolytic activity against MOLT-4 and a weaker reactivity against the bladder tumour cell lines T24 and RT4. The natural killer (NK)-susceptible K562 cells were not lysed. Two of the CD3+CD4+ clones (K91 and K914) showed a helper activity in pokeweed mitogen (PWM)-induced IgG production by B cells. These cells differed in the expression of CD45R and CDw29 antigens, as defined by the monoclonal antibodies 2H4 or D10D11 and 4B4. When stimulated with PWM for 48 or 72 h, clone K91 and an additional CD4-positive clone (K913) secreted a factor into the supernatants which helped B cells to produce IgG. The K913 supernatant also induced some IgM production. The supernatant obtained after similar stimulation of K914 cells was inactive. None of these supernatants induced B cells to proliferate when tested together with phorbol myristate acetate (PMA). However, when K91 and K914 cells were activated with phytohaemagglutinin (PHA) for 48 or 72 h, the supernatant from K91 was strongly helpful in B-cell proliferation, whereas the supernatant from K914 cultures was only moderately active. In conclusion, we have established human T helper clones that release different factors supporting either B-cell proliferation or maturation when stimulated with PWM or PHA.