Induction of Unresponsiveness and Immunity in Newborn and Adult Mice with Pneumococcal Polysaccharide

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Abstract
Summary: Newborn mice can be immunized or rendered unresponsive (paralyzed) to type II pneumococcal polysaccharide as determined by their response to subsequent pneumococcal challenge. When challenged at a given age, relatively high doses of S II at birth lead to unresponsiveness, somewhat lower doses lead to immunity, and very low doses have no apparent effect. Unresponsiveness induced by the neonatal injection of S II disappears slowly with time and is followed, without further injection of antigen, by immunity. Immunity induced by neonatal injection of small doses of S II diminishes slowly with time. There is no apparent difference between newborn and young adult mice with respect to ease of induction of unresponsiveness to S II. The data suggest that newborn mice can be immunized with S II more effectively than can older mice. It is suggested that dose and persistence of antigen, rather than neonatal presentation, are more important factors in the induction and maintenance of immunologic unresponsiveness. When the amount of antigen present in the animal decreases below a critical level the animal ceases to be unresponsive and is, in fact, immunized by the residual antigen present.