FREQUENCY OF T-CELL PROGENITORS IN NUDE-MICE

The hypothesis that prothymocytes are distinct from and regulated inde pendently of multilineage hemopoietic progenitors was tested by enumer ation of these two cell populations in normal versus congenitally athy mic (nude) mice. The absence of a thymus and of peripheral T cells in nude mice had no effect on the frequency of either multilineage progen itors (day 12 CFU-S) or prothymocytes (CFU-T), suggesting that there i s no feedback regulation of CFU-T frequency. Thymus seeding from the b one marrow is therefore likely to be regulated by the availability of niches for prothymocyte maturation, rather than by feedback control of prothymocyte production.