Maintenance of lymphocyte surface Ig by mitogen stimulation in vitro

In 4 to 24 hr cultures of rabbit lymphoid cells in medium supplemented with autologous serum, most B cells lost their surface Ig as assayed by rosette formation with anti-Ig antibody-coated erythrocytes. This loss was prevented by adding selected mitogens such as streptococcal mitogen (SM), lipopolysaccharide, and concanavalin A or by supplementing the medium with fetal calf serum. When SM was added at various times to the cultures (1, 2, 3, and 4 hr), it was effective in maintaining the approximate level of Ig-bearing cells present at the time of its addition but was ineffective in restoring the level of Ig-bearing cells present at the time the cultures were intiated. Very small, submitogenic doses of SM were sufficient to maintain the level of Ig-bearing cells. The data suggest that lymphocytes require continuous stimulation to maintain their surface receptors.