Staphylococcus aureus Cowan I-induced immunoglobulin production in human cord blood lymphocytes

Human cord blood mononuclear cells (MNC) were stimulated with antibiotic killed Staphylococcus aureus Cowan I bacteria (S. aureus) or pokeweed mitogen (PWM) and cultured for 6 days. Immunoglobulin synthesis and secretion was measured with the indirect protein A plaque-forming cell (PFC) assay. All 14 cord blood specimens stimulated with S. aureus produced PFC comparable to that measured in adult peripheral blood cultures. PWM induced only minimal responses in cord MNC whereas good responses were demonstrated in adult cell cultures. The majority of the cord blood immunoglobulin synthesizing cells produced IgM, however, significant production of IgA was also seen. These observations were confirmed by detection of intracytoplasmic immunoglobulin in plasma cells with the use of fluorescent anti-immunoglobulin antibodies.