Immunosuppression by an immunogenic immunomodulating mycobacterial fraction is correlated to changes in phenotype distribution of murine lymphoid cells.

Previously reported studies revealed that extensive immunization with the Methanol Extraction Residue (MER) of BCG tubercle bacillus in Incomplete Freund's Adjuvant (IFA) induced marked suppression of T and B cell functions in vivo and in vitro. The purpose of the present work was to determine whether immunosuppression induced by hyperimmunization with MER is correlated with changes in morphological characteristics and in phenotype pattern of spleen and peritoneal lymphoid cells. Hyperimmunization with MER resulted in a marked increase in the number of spleen cells and in enlargement and granulation of spleen and peritoneal cells. Similar changes in size and granulation were also observed in isolated fractions of splenic T and B cells. Extensive immunization with MER also induced marked decrease in the total number of T cells (Thy 1,2 positive). The decrease in T cells was observed in all three T-cell subsets investigated: Lyt-1, Lyt-2 and L3T4 positive. Although the number of splenic B cells was decreased in samples (10,000 cells), taken from MER hyperimmunized mice, this decrease was compensated by overall increase in the number of spleen cells. The marked decrease in the percentage of splenic T cells was counterbalanced by marked increase in the splenic macrophage population: increase in MAC-1, MAC-2 and MAC-3 positive cells. It is concluded that extensive immunization with MER induces morphological changes in spleen and peritoneal cells, marked decrease in the number of splenic T cells and marked increase of the splenic macrophagic population. It is postulated that these changes are correlated with induction of immunosuppression by a similar procedure of extensive immunization with the agent.