Mechanism of action of suppressor cells. In vivo concanavalin-A-activated suppressor cells do not directly affect B cells.

The addition of a small proportion (10%) of in vivo concanavalin-A (Con-A)-activated spleen cells to normal spleen cell cultures suppressed the primary immune response to sheep erythrocytes (SRBC) but had no effect on the thymus-independent primary immune response to 3,5-dinitro-4-hydroxy-phenacetyl-conjugated lipopolysaccharide. When Con-A-activated cells were added after 24 h, there was no suppression of the anti-SRBC response but rather an enhanced response when few cells were admixed. Con-A-activated cells did not influence activation of normal cells by polyclonal T- and B-cell activators. It is concluded that Con-A-induced suppressor cells do not act on B cells but rather on helper cells (T cells or macrophages) at a very early stage of the immune response to thymus-dependent antigens.