Unique phenotype and distinct TCR V beta repertoire in human peripheral blood alpha beta TCR+, CD4-, and CD8- double...

TCR-alpha beta+ CD4- CD8- double-negative (DN) T cells represent a small, poorly defined T cell subset in human peripheral blood that has been postulated to be potentially autoreactive. To define some of the characteristics of this subset of T cells, DN cells and CD4+ and CD8+ single-positive (SP) cells were purified from the peripheral blood of six unrelated individuals by a combination of positive selection and depletion using mAb conjugated to immunomagnetic beads. Purified DN cells were found to be enriched in cells expressing HLA-DR and the NK cell marker, CD56, when compared to the SP population. Furthermore, in contrast to SP cells that express the adhesion marker CD44, DN cells were found to express very little, if any, CD44. When the V beta TCR repertoires of DN and SP (CD4+ and CD8+) cells, determined by quantitative (q) PCR, were compared all three populations were found to be considerably different. Furthermore, several V beta segments (V beta 11 and V beta 19) were consistently expressed at higher levels on DN cells than on SP cells. The TCR repertoires of both DN and SP cells were frequently characterized by dominance of one or more V beta segments that could in some instances be shown to be restricted to the CD45RO+ ("memory") population. However, differences in TCR repertoire between DN and SP cells were observed even when CD45RO+ cells were removed before qPCR analysis. These studies suggest that the TCR repertoires of DN and SP cells are determined by different selection mechanisms and that DN and SP cells are directed against different Ag.