CD4dullCD8bright double-positive T-lymphocytes have a phenotype of granzyme BposCD8pos memory T-lymphocytes

Background. T-lymphocytes that co-express CD4 and CD8 antigens may be found in small percentages in the peripheral blood of healthy individuals, and have a CD4(bright)CD8(dull) phenotype. CD4(dull)CD8(bright) T-lymphocytes have been found only in temporal association with some viral infections. Methods, Four-colour flow cytometric analysis of peripheral blood mononuclear cells from a renal transplant recipient with cytomegalovirus infection was performed. Results. A small but clearly distinguishable subpopulation of CD4(dull)CD8(bright) double-positive T-lymphocytes was detected, that exhibited phenotypic characteristics of cytotoxic T-lymphocytes and were granzyme B positive. Furthermore, no naive cells appeared to be present within this subpopulation. Conclusions. CD4(dull)CD8(bright) double-positive T-lymphocytes are enriched for memory and effector cytotoxic T cells.