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 5096 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.