In vitro response of human peripheral blood lymphocytes of protein A. DNA synthesis and generation of cells synthesizing the three major classes of Ig.

Increased DNA synthesis and immunoglobulin secretion was observed in human peripheral blood lymphocytes (PBL) cultured in vitro with soluble protein A from Staphylococcus aureus (Sp-A). Optimal Ig secretion was obtained in 6 day cultures containing 1 x 10(6) cells/ml and 10 microgram/ml Sp-A. The presence of 5 x 10(-5) M 2-mercaptoethanol in the culture medium as well as careful selection of foetal calf serum were needed for optimal results. In response to Sp-A stimulation, the three main classes of immunoglobulins were secreted by PBL. In some individuals, concentration of Sp-A optimal for IgG and IgM secretion inhibited IgA production. Immunoglobulin-containing cells were less abundant (0.5--5% of total cells) and smaller in Sp-A than in PWM-stimulated cultures (5--15%). The data suggest that Sp-A and PWM stimulated different subsets of circulating lymphocytes.