Comparison of the immune response potential of newborn mice to T-dependent and T-independent synthetic polypeptides.

Newborn mice do not, in general, produce antibodies during the 1st week of life; this inability to respond immunologically has been attributed to lack of functional macrophages and T cells. To determine whether B cells of newborn mice are functionally mature and therefore capable of producing antibodies to thymus (T) independent antigens, the response of 1-9-day-old C3H/HeJ mice injected with a thymus-independent polypeptide, poly(DTyr,DGlu)-polyDPro- -polyDLys was compared to that of their littermates injected with a thymus-dependent immunogen, poly(LTyr,LGlu)-polyLPro- -polyLLys. No antibodies were detected in 1- or 2-day-old mice immunized with the T-dependent antigen, as revealed by haemagglutination and haemolytic plaque-forming cell assays, performed 6 days after injection of the antigen. Injection of 3-day-old animals with the thymus-dependent immunogen resulted in significant immune responses which increased with age. In contrast, 1- and 2-day-old mice responded to the T-independent immunogen with high antibody levels, however, in 3-day-old injected mice, the levels were lower. When 3-day-old nude mice were injected with this antigen, no decrease in the immune response was observed. Thus, newborn mice respond immunologically to a thymus-independent antigen injected at the first 2 days after birth and the antibody levels decrease with maturation of the thymus.