Major Histocompatibility-Restricted Cytolytic T-Lymphocyte Precursors from the Thymus of In Vivo Primed Mice: Increased Frequency and Resistance to Anti-Lyt-2 Antibody Inhibition

Abstract

The thymus is the primary site for the generation of immunocompetent T lymphocytes (Miller and Osoba 1967). It was generally assumed that there was an unidirectional flow of T cells from the thymus to peripheral lymphoid tissues, but recently evidence has accumulated suggesting that there may be recirculation of peripheral T lymphocytes back to the thymus (Naparstek et al. 1982) and that the thymus may actively participate in an immune response. The functional participation of the thymus in an immune response was demonstrated by showing an increase in the frequency of thymic cytolytic T-lymphocyte precursors (CTL-P) responding to minor histocompatibility (minor-H) antigens following in vivo priming (Fink et al. 1984). Furthermore, in this study, it was suggested that the increased thymic content of CTL-P was the sum of three independent sources. Thus, prethymic and intrathymic T cells were primed within the thymus, but in addition there was evidence for recirculation back to the thymus of peripheral T cells.