Studies on immunological paralysis. V. The influence of molecular weight on the immunogenicity, tolerogenicity and antibody-neutralizing activity of the 3 pneumococcal polysaccharide.

Type 3 pneumococcal polysaccharide (SIII) with average molecular weight 220,000 was depolymerized by heating aqueous solutions under pressure. The immunogenicity and tolerogenicity of fractions with molecular weights of 121,000, 31,000 and 4000 were compared with the native antigen by means of direct splenic PFC and serum haemagglutinin assays. Fall in molecular weight was accompanied by progressive reduction in both immunizing and tolerance-inducing properties. The 4000 molecular weight preparation (ten glucuronosidoglucose units) was feebly immunogenic and non-tolerogenic, although known to contain intact determinants. Depolymerization was also correlated with loss of antibody-neutralizing activity. Paralysis with SIII involves `high-zone' tolerance in the B lymphocyte population. The proposition is discussed that immunogenicity is here a necessary characteristic of the inducing antigen.