Cell surface markers in cord blood leucocytes after stimulation with lipopolysaccharide B

T- and B-lymphocyte markers were studied in cord blood cells cultured with lipopolysaccharide B (LPS). Cells cultured with leucoagglutinin (LA) and pokeweed mitogen (PWM) were used as controls. LPS-induced lymphoblasts were negative for surface Ig, positive for intracellular Ig and did not form rosettes with sheep red blood cells (SRBC). LA-activated cells formed rosettes with SRBC, while PWM cultures showed a varying proportion of surface Ig-positive or SRBC rosetting cells, dependent on the time of culture. About 50% of both LA- and LPS-activated lymphoblasts formed EA rosettes (specific for Fc receptors) and EAC rosettes (specific for complement receptors). The response of foetal cells to LPS was reduced when lymphocytes obtained from Isopaque-Ficoll gradients were passed through nylon wool columns, whereas this procedure led to an increased response to LA. Thus LPS-activated foetal leucocytes are B lymphocytes expressing intracellular but not surface Ig.