Antigen-antibody complex-induced immunosuppression. Effect of F(ab')2 antibodies and protein A

The addition of immune complexes (anti-horse red blood cell (HRC) antibodies plus HRC) to spleen cell cultures activated by lipopolysaccharide (LPS) selectively suppressed the anti-HRC plaque-forming cell (PFC) response, but did not affect the PFC response to sheep red blood cells (SRC). The degree of suppression was directly related to the concentration of immune complexes. F(ab')2 preparations suppressed as efficiently as intact IgG, although the ability of the F(ab')2 preparation to lyse the red cells was abolished. The addition of protein A to the immune complexes (using intact antibodies) did not affect the degree of suppression. The findings suggest that immune complex-induced suppression of polyclonal B cell activation is caused by constant parts of the light or heavy chains of the antibodies other than the Fc part.