The immune response against two epitopes on the same thymus-independent polysaccharide carrier. II. Enhanced anti-hapten responses by injection of the unconjugated carrier.

Dextran B512 preparations of various mol. wts induced polyclonal antibody synthesis . The efficiency of activation decreased with the mol. wt. Dextran also markedly enhanced the anti-hapten (fluorescein-isothiocyanate—FITC) response after injection of immunogenic doses of FITC dextran. The adjuvant activity decreased with the mol. wt of unconjugated dextran. The concentration of dextran which was necessary for adjuvanticity induced complete tolerance to the α1-6 epitope. Native dextran acted as an effective adjuvant and was capable of inducing polyclonal activation even in mouse strains that fail to produce antibodies to the α 1-6 epitope of dextran B512. The adjuvant property of dextran did not require T cells. Lipopolysaccharide from did not act as an adjuvant for the anti-FITC response after injection of immunogenic doses of FITC-dextran. Since unconjugated dextran markedly enhanced the specific anti-FITC response after injection of FITC-dextran, it is concluded that the polyclonal activating property of dextran is capable of delivering an activation signal for the induction of specific immune responses to haptens coupled to dextran. Since LPS was not an adjuvant for the immune response to FITC-dextran, although LPS is known to be a potent adjuvant for heterologous thymus-dependent red cell antigens, it is likely that LPS and dextran act as polyclonal B-cell activators on different B cell subpopulations.