Activation of human T lymphocytes by soluble protein A

The proliferative response of highly purified human peripheral blood or tonsil lymphocytes in the presence of soluble protein A (SpA) was investigated. SpA was shown to be a potent mitogen for T lymphocytes from peripheral blood or tonsils. Conversely, the non-T lymphocyte population from peripheral blood responded poorly to SpA, and SpA did not stimulate non-T lymphocytes from tonsils. The addition of mitomycin-treated T lymphocytes from peripheral blood enhanced the response of blood non-T lymphocytes to protein A. This effect was not found when non-T lymphocytes isolated from tonsils were cultured with mitomycin-treated T lymphocytes. The proliferative response of unseparated cells or purified lymphocyte populations was enhanced when adherent cells were added to the cultures. It is concluded that the soluble form of protein A activates mainly T lymphocytes and does not induce B lymphocyte proliferation.