Interleukin 2 receptors on human B cells. Implications for the role of interleukin 2 in human B cell function

In the present study, we examined the expression of interleukin 2 (IL-2) receptors on normal human B cells as well as established B cell lines. Anti-Tac monoclonal antibody did not bind to freshly separated normal human B cells. Unexpectedly, with the appropriate activation of the normal B cells by anti-mu antibody, phorbol myristate acetate, or Staphylococcus aureus Cowan I (SAC), Tac antigen was induced on the activated B cells. Anti-Tac antibody showed consistent reactivity with two B cell lines that were infected by human T cell leukemia virus (HTLV) and some reactivity with two out of eight Epstein-Barr virus-transformed B cell lines established from normal adult donors. Immunoprecipitation analysis revealed that antigens of similar size with a molecular weight of 50,000-60,000 can be precipitated with anti-Tac antibody from phytohemagglutinin-stimulated normal T cell blasts and normal activated B cells, as well as a cloned B cell line. Binding assays of IL-2 on normal activated B cells and on the cloned B cell (HS1) revealed that B cells have significantly fewer sites and lower-affinity IL-2 receptors compared with phytohemagglutinin-stimulated normal T cell blasts. Finally, biological properties of the IL-2 receptor on B cells were examined by incubating B cells with recombinant IL-2. It was found that moderate concentrations of IL-2 induce significant enhancement of proliferation and differentiation in SAC-activated normal B cells. These results suggest that normal B cells may express functional IL-2 receptors or closely related proteins and thus IL-2 may play a significant role in the modulation of B cell function.