Identification and characterization of pro-T lymphocytes and lineage- uncommitted lymphocyte precursors from mice with three novel surface markers

The study of prethymic stages of T cell development has been limited because specific markers for mouse pro-T lymphocytes were not available. We developed a panel of rat monoclonal antibodies (mAbs) that bind to our pro-T lymphocyte clones obtained from bone marrow of young adult mice and the thymus of 14-d-old embryos. The mAbs, called Joro 30-8, Joro 37-5, and Joro 75, were found to bind to all pro-T clones tested but not to cell lines representing later stages of T cell development, B lymphocyte, or myeloid lineages. We determined the frequency and tissue distribution in normal and immunodeficient mouse strains as well as the ontogeny in liver and thymus of cells positive for these mAbs. The results were consistent with the pattern of reactivity observed with cell lines. We isolated Joro 30-8+, Joro 37- 5+, and Joro 75+ bone marrow cells by cell sorter and found that: (a) phenotypically, they are Thy-1+, CD4-, CD8-, CD3-, B-220-, IgM-, F4/80- , and PgP-1+; (b) they grew in response to the combination of interleukin 3 (IL-3) + IL-4 or IL-3 + IL-4 + IL-6; and (c) Joro 37-5+ and Joro 75+ marrow cells gave rise to mature T lymphocytes but not to B lymphocytes, while Joro 30-8+ marrow cells generated both T and B lymphocytes after 8-12 wk of transfer into severe combined immunodeficient (Scid) mice. In normal mice subjected to 600 rad of irradiation to induce a wave of thymus recolonization, we found by flow fluorocytometry analysis that Joro+ cells entered the thymus 2 d after irradiation, expanded during the next 4 d, and underwent further differentiation, and from day 8 up to day 21, post-irradiation Joro+ cells were no longer detectable in the thymuses. Immunohistochemical analysis of normal thymus shows the presence of very few Joro 30-8+, Joro 37-5+, and Joro 75+ lymphoid cells in the subcapsular area and outer cortex but not in the medulla. The kinetic analysis of tissue sections from thymuses at various days post-irradiation suggests that Joro+ cells enter the thymus via blood vessels through the subcapsular and outer cortex areas; subsequently, these cells seem to migrate to the inner cortex without reaching the medulla, and give rise to Joro- thymocytes.(ABSTRACT TRUNCATED AT 400 WORDS)