Human CD8 T cells of the peripheral blood contain a low CD8 expressing cytotoxic/effector subpopulation

Heterogeneity of lymphocyte populations demonstrates the diversity of cellular immune responses and provide a better understanding of the immune system. CD3(+) CD8(+) T cells exhibit a low CD8 expressing (CD8(low) ) population in flow cytometric analysis of peripheral blood T cells. In healthy donors, this population consists of 0.2-7.0% of all CD8 T cells. The majority of the CD8(low) T cell population showed an elevated expression of CD25, CD45RA, and CD95L, and low levels of CD28, CD62L and CD45RO. Circulating CD8(low) T cells resemble cytotoxic effector cells because they express cytolytic mediators and are able to execute cytotoxicity. A restricted T cell receptor profile with increased Vbeta9, Vbeta14 and Vbeta23 expression was observed and the CD8(low) T cell population contain Epstein-Barr virus-specific T cells. Therefore, the CD8(low) population represent a subset of activated CD8 effector T cells, resulting most probably from a continous and/or balanced immune response to intracellular pathogens.