Immunosuppressive activity of BCG: effects of adjuvant disease, lymphocyte subpopulations, and homing of thoracic duct cells in rats.

Administration of BCG by various dosage schedules suppressed adjuvant disease in rats. BCG administration produced an initial increase, followed by a depression, of the phytohemagglutinin response of purified blood lymphocytes. An increase in absolute and relative numbers of bursa-equivalent (B)-cells followed BCG administration, concurrent with a decrease in the phytohemagglutinin responsiveness. With adjuvant alone, there was a diminution in phytohemagglutinin response and an increase in number of B-cells; the latter occurred immediately after adjuvant injection and also when the generalized disease appeared. When both BCG and adjvant were present, parallel increases of phytohemagglutinin responsiveness and B-cell numbers resulted. The pattern of tissue localization of radioactively labeled thoracic duct cells from normal or BCG-treated donors given to normal, BCG-treated, adjuvant-injected, and BCG-treated + adjuvant-injected syngeneic recipients indicated significantly greater homing to the thymus and decreased localization to the bone marrow when BCG had been given to either donors or recipients. When labeled thymus cells were used, only the decreased bone marrow localization was noted. These observations suggest that the suppressive effect of BCG may be mediated through modification of the lymphocyte recirculation pattern, possibly resulting from alterations in lymphocyte recognition sites.