Absence of growth by most receptor-expressing fetal thymocytes in the presence of interleukin-2

Abstract

The growth of mature T cells is regulated by receptors for interleukin-2 (IL-2) and by IL-2 itself. Binding of antigen to T-cell antigen receptors induces the expression of IL-2 receptors, and binding of IL-2 to these receptors induces transferrin receptor expression and is sufficient to promote the growth of T cells for several days^1,2. However, nothing is known about the growth requirements of pre-T cells. We have therefore studied the dividing population of T-cell precursors which carry the Thy-1 surface antigen, but lack surface antigens Ly2 and L3T4; these cells are present in 14-day-old embryonic thymus^3,4. If the thymus is removed at this stage and placed in organ culture, all lymphocyte subpopulations normally present in thymuses of adult mice develop in vitro^4,5, that is, the nonfunctional Ly2⁺, L3T4⁺ population and the functional Ly2⁺, L3T4⁻ and Ly2⁻, L3T4⁺ populations⁴. We now report that, in contrast to their progeny, the early Ly2⁻, L3T4⁻ cells express large amounts of IL-2 receptors, but most of them do not grow in IL-2-containing media outside the thymus. In contrast to dividing mature T cells, most fetal thymocytes express low amounts of transferrin receptors.