HIGH-FREQUENCY, BUT REDUCED ABSOLUTE NUMBERS OF RECENT THYMIC MIGRANTS AMONG PERIPHERAL-BLOOD T-LYMPHOCYTES IN DIABETES-PRONE BB RATS

In rats, RT6 and CD45RC are expressed by mature peripheral T cells, Th e underrepresentation of T cells expressing these markers in the T lym phocytopenic BE rat might therefore be a reflection of a relatively im mature T cell population. With the use of Thy-1 as a marker for recent thymic migrants, it was demonstrated that BE rats indeed have a pheno typically less mature T cell population than age-matched control rats. However, this could not account for the reduced percentages of RT6(+) and CD45RC(+) T cells, as these were also decreased among mature Thy- 1(-) T cells of BE rats. Although relatively overrepresented, absolute numbers of Thy-1(+) T cells were reduced in BE rats, Absolute numbers of mature Thy-1(-) T cells were also reduced in BE rats, but to a muc h larger degree than would proportionally be expected, Our findings ta ken together led us to conclude that both reduced thymic output and a defect in peripheral expansion are involved in the T lymphocytopenia o f EB rats. (C) 1995 Academic Press, Inc.