The Generation of Antigen Sensitive Cells in the Newborn Mouse

Abstract

Abstract The development of immunocompetence in C57BL/6 mice was studied during the first 2 weeks after birth. The ability to mount a direct plaque-forming cell (PFC) (IgM) and indirect (IgG 2a) response was determined as a function of age. Responsiveness at a given age was determined in two systems: 1) by direct immunization of intact mice and 2) by stimulation of spleen cells which had been transferred to irradiated syngenic recipients. The kinetics of the antibody response given by transferred spleen cells did not vary with the age of the donor. Spleen cells from 1- to 3-day-old mice gave a direct PFC response only in irradiated recipients; when thymus cells from adult mice were injected together with these spleen cells and indirect PFC response also was facilitated. The rate of increase in responsiveness for the direct PFC response was markedly different initially from that of the indirect PFC response; after 4 days both responses increased exponentially with the age of the donor. The rate of increase in responsiveness of intact mice was very low until age 9 to 10 days at which time the rate increased dramatically; this increase was attributed to the maturation of the antigen-processing system. The responsiveness during the first 2 weeks after birth thus depends on three factors: 1) the rate of seeding of antigen sensitive bone marrow-derived “B” lymphocytes, 2) the rate of seeding of thymus derived lymphocytes and 3) the rate of maturation of the antigen-processing system. The indirect (IgG 2a) PFC response is markedly dependent on both factors 2 and 3 whereas the direct (IgM) response is less dependent on both of these factors.