Staphylococcus aureus cowan I and Branhamella catarrhalis as B lymphocyte mitogens. Culture conditions for optimal DNA synthesis and selective stimulation of human B lymphocytes.

Staphylococcus aureus Cowan I and Branhamella catarrhalis that selectively stimulate human B lymphocytes to increased DNA synthesis in serum-free culture media were shown to do so also in 3 day cultures in medium containing human serum or albumin. After this time the transformed cells expressed little or no surface-bound immunoglobulin and did not form rosettes with sheep erythrocytes. When lymphocytes were cultured with bacterial mitogens in the presence of serum or albumin for more than 3 days transformed T cells appeared. The bacteria induced antibody production mainly of IgM class in lymphocytes cultured in albumin supplemented medium.