AbstractWe have studied the effect of pertussis toxin (PT) onin vivopriming of T lymphocytes to insulin. Mice were immunized with bovine insulin in complete Freund's adjuvant and antigen-specific DNA synthesis was measured in lymphoid cell suspensions from lymph nodes and spleens. Insulin-specific response was greatly enhanced both in spleen and lymph nodes if mice were given PT at the time of immunization. Mice given PT presented 3 times more cells in spleen and 4 times less in lymph nodes. However, the major antigen-specific response was still observed in lymph nodes. PT had a strong mitogenic effectin vitroon lymph node cells but a weak effect on spleen cells indicating that the adjuvant activity of PT involves other effects besides the mitogenic activity.