Normal development of the thymus‐dependent limb of humoral immune responses in mice

Abstract The capacity of mice to produce antibody‐forming cells (AFC) to sheep erythrocytes and to low doses of two haptenated proteins increases logarithmically with age in the postnatal period. This increase is prevented by thymectomy. These findings, together with those on the ability of suckling mice to make high numbers of AFC to high doses of at least one of the antigens used, indicate that T cells are the limiting cell type in neonatal humoral immune responses. An analysis of variance of the number of AFC in individual spleens as a measure for T cells showed that the data are in agreement with random generation and subsequent proliferation of these cells during ontogenesis. Different antigen reactivities carried by these cells seem to arise at different times during fetal life.