Postnatal development of functional T cell subsets in the mouse: a frequency analysis of mitogen reactive precursors of proliferating, of cytotoxic and of IL 2 producing T cells

Abstract

In order to study the postnatal development of functional T cell subsets in the mouse, a mitogen-driven limiting dilution culture system was used for a precursor frequency analysis of proliferating, of cytolytic and of IL 2-producing T cells, respectively, present in spleen and thymus of mice from neonatal to adult age. In adult mice, the majority (up to 100%) of splenic T cells was capable to respond to Concanavalin A. In contrast, an up to tenfold lower frequency of mitogen-reactive precursors was found within positively selected Thy-1+ spleen cells of neonatal mice. Within this fraction of Con A reactive neonatal T cells, there was an apparent imbalance in the CTLp/PTLp ratio within the first to second week after birth. Accordingly, significant numbers of immunocompetent precursors of HTLp were detected in the spleen shortly after birth, while the vast majority of CTLp developed later on. This differential development of CTLp and PTLp was not seen with thymocytes of the same mice, where from the age of two to three days on up to the adult age the frequency of both CTLp and PTLp remained largely unchanged. Analysis of the Lyt-antigen expression, in addition, revealed phenotypical differences between neonatal and adult Thy-1+ spleen cells, such that Lyt-2 antigen density but not the proportion of Lyt-2 positive T cells, was considerably lower in newborn mice. An age related increase in both Lyt-2 antigen density and CTLp frequency was parallelled by the rapid increase in the total number of splenic T cells during the second and third postnatal week, reaching 60-70% of adult values. At this time, a normalisation of the CTLp/PTLp ratio at approximately 0.4 had occurred.