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Age-Dependent Changes in Sensitivity to Antigen in the Mouse

From the Department of Immunology, University of Manitoba, 795 McDermot Avenue, Winnipeg, Canada, R3E OW3

Abstract

The maturation of antibody responsiveness was studied in C57BL/6 mice by comparing the sensitivity to antigen of 12-day-old and 12-week-old animals. Sensitivity was established by constructing dose response curves for the IgM and IgG2a PFC responses. Twelve-day-old animals yielded dose response curves with well defined maxima and relatively narrow band widths (BW). The optimal antigen doses for the two antibody classes studied were different—1.2 x 10⁹ sheep red cells for the IgM response and 3.8 x 10⁹ for the IgG2a response. Adult (12-week-old) animals yielded dose response curves significantly different from those of young mice. Optimal antigen doses were lower in the adult group (2.9 x 10⁸ for the IgM and 1.0 x 10⁹ for the IgG2a PFC response), indicating an increased sensitivity to this antigen. The BW (ratio of the two antigen doses which elicited a response equal to 50% of the maximum) of the adult dose response curves were four times greater than the BW obtained with the 12-day-old group. In addition, a low cross-reactivity was demonstrated between sheep red cells and the lipopolysaccharide antigen prepared from Escherichia coli. The increases which occurred with age in both the sensitivity and BW of the responses are discussed in terms of: 1) a thymus-derived cell deficiency in the young mice; 2) the selection of receptor sites by cross-reacting environmental antigens; and 3) changes in the antigen-processing system. It was concluded that the last of these possibilities formed the basis for the changes in sensitivity which were observed.