Suppression of the primary immune response in vivo to sheep red blood cells by B-cell mitogens.

Polyacrylic acid (PAAC), lipopolysaccharide (LPS), dextran sulphate (DS) and purified protein derivative of tubercle bacilli (PPD), compounds mitogenic for B lymphocytes in vitro, suppressed the immune response of mice to SRBC in vivo, when injected 4-2 days before immunization. The same compounds enhanced the immune response when injected half an hour before immunization of the animals with a suboptimal antigen dose. A subsequent injection of PAAC given shortly before immunization, abolished the immunosuppressive effect expected by pretreatment of the animals with either PAAC or LPS. A second injection of LPS abolished the immunosuppressive effect of LPS only. The results indicate that when B lymphocytes react with a mitogen in the absence of a particular antigen, they temporarily lose their capacity to respond to antigen.