Studies on immunological paralysis. IX. The immunogenicity and tolerogenicity of levan (polyfructose) in mice.

The immunological response to native levan (a fructose homopolymer with molecular weight 2×107) has been studied in (DBA/1×CBA-T6T6)F1 mice by passive haemagglutination and plaque-forming cell (PFC) assays. It resembles type-specific pneumococcal polysaccharide (SSS) in eliciting a prolonged humoral antibody response over a wide dose range (0.0001–100 μg) and in inducing longlasting `high zone' tolerance with a single injection (1 mg or more). Other similarities include an exclusively IgM response, independence of synergy with thymus-derived lymphocytes and absence of immunological memory. On the other hand, parallelism between serum haemagglutinin and PFC levels following all doses of antigen implies that higher immunizing doses of levan, unlike SSS, do not engage in peripheral neutralization of antibody. It was concluded from studying the fate of 14C-labelled levan that this was attributable to more rapid elimination from the circulation and subsequent slow metabolism of this polysaccharide. Levan also differs from SSS in inducing tolerance directly, without a detectable prior immune phase.