Expression of Tac antigen on activated normal human B cells

Two-color fluorescence analysis revealed that Tac antigen, which was previously reported to be restricted to T cells, was expressed on a proportion of normal B cells activated by Staphylococcus aureus Cowan I (SAC). Immunoaffinity-purified interleukin 2 (IL-2) induced the proliferation of SAC-activated B cells, and the proliferation was completely inhibited by anti-Tac antibody, which blocked the membrane binding and action of IL-2. These results suggest that an IL-2 receptor system is directly involved in the B cell immune response.