DIFFERENTIAL CONTRIBUTION OF THYMIC OUTPUTS AND PERIPHERAL EXPANSION IN THE DEVELOPMENT OF PERIPHERAL T-CELL POOLS

The number of peripheral T cells in mice increases up to 100-fold in t he first few weeks of life. We have followed the fate of Thy-1 congeni c T cells transferred into newborn recipients, to evaluate the relativ e contribution of thymic output versus peripheral expansion in the con stitution of peripheral T cell pools during post-natal development. Th e results show that in normal animals there is essentially no peripher al expansion of T cells, which show slow turnover rates (1 to 2 months ) along that time period. The rates of cell accumulation in the periph ery require, therefore, an average of 1 x 10(6)-2 x 10(6) mature thymi c emigrants/day for the first 3 weeks of life.