ANALYSIS OF THYMIC SUBPOPULATIONS EXPRESSING THE ACTIVATION ANTIGEN GL7 - EXPRESSION, GENETICS, AND FUNCTION

Previously, we reported an mAb, GL7, that defines an activation Ag exp ressed by in vitro-stimulated B and T cells as well as by a subpopulat ion of thymocytes. The current study analyzes the GL7-expressing popul ations of adult and fetal thymus and demonstrates that: 1) The majorit y of GL7(+) adult thymocytes are CD4(+)CD8(-) cells that are CD3 epsil on(high), TCR-alpha beta(high), HSA(low), and bimodal for CD69 express ion. The 3G11(-)6C10(-) subset of CD4(+)CD8(-) thymocytes is enriched in GL7-expressing cells. 2) Strain differences exist in the expression of GL7 on adult CD4(+)CD8(-) thymocytes; 21.9 +/- 5.9% of BALB/c CD4( +)CD8(-) thymocytes are GL7(+), whereas 4.4 +/- 1.7% of C57BL/6 CD4(+) CD8(-) thymocytes are GL7(+). The low GL7 expression phenotype is domi nant in CB6F1 thymocytes (7.0 +/- 2.0%), and analysis of BALB/c x CB6F 1 mice suggests that low GL7 expression is determined by multiple gene s. 3) CD4(+)CD8(-) GL7(+) thymocytes from BALB/c mice, but not C57BL/6 mice, are skewed toward a high proportion of V beta 8(+) cells. 4) Ad ult GL7(+) CD4(+)CD8(-) thymocytes can be activated by TCR-specific st imuli to proliferate and to secrete high amounts of IL-4. 5) Fetal thy mocytes contain GL7(+) cells, which are predominantly CD4(-)CD8(-), HS A(low), CD69(-), and bimodal for TCR-gamma delta. Thus, GL7 expression defines a subpopulation of functionally competent TCR-alpha beta(+) C D4(+)CD8(-) thymocytes as well as TCR-gamma delta(+) and TCR(-) subpop ulations of fetal CD4(-)CD8(-) thymocytes.