Induction of Suppressor Cells by Immunostimulants

Bacillus Calmette-Guerin (BCG; 18, 19), a viable attenuated strain of Mycobacterium bovis, and Corynebacterium parvum (C. parvum, 20), a gram-negative bacterium, are widely employed as immunostimulants though their precise mechanism of action is unknown. Functionally, BCG enhances antigen clearance and phagocytosis, augments cellular and humoral immune responses, and increases resistance to infection (18, 19). In addition, activation of thymus-derived cells (T cells) by BCG has been reported (21), but this may only occur in the presence of small levels of macrophages (29). Both BCG (19) and C. parvum (20,22) activate the macrophages, and consequently, an efficient killing capacity may be found in these cells. Humoral and cellular immune responses may be enhanced in animals treated with BCG (19) or C. parvum (20) because of the ability of these immunostimulants to augment the capacity of macrophages to process and present antigen to lymphocytes. In addition, C. parvum and BCG can augment the activity of NK cells (23).