Role of antigen in the regulation of the immune response to dextran B512.

Dextranase mixed with dextran in vitro or injected into mice before the antigen abolished the immunogenicity of both thymus-dependent and thymus-independent forms of dextran. Dextranase could degrade dextran in vivo even when given 6-15 days after the antigen. Dextranase injected after the antigen suppressed the immune response when given 24 h, but not 48 h, after the antigen, indicating that the antigen must interact with the immune system for 48 h to initiate a response. Thereafter , the B cells are independent of further antigen stimulation. The induction of autoanti -idiotypic anti-dextran antibodies was abolished if dextranase was given 24 h, but not 48 h, after the antigen, indicating that anti-idiotypic antibodies can be induced in the absence of antigen or immune complexes once anti-dextran antibodies have been synthesized.