CD4dullCD8bright double-positive T-lymphocytes have a phenotype of granzyme Bpos CD8pos memory T-lymphocytes

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 CD4brightCD8dull phenotype. CD4dullCD8bright T-lymphocytes have been found only in temporal association with some viral infections. Four-colour flow cytometric analysis of peripheral blood mononuclear cells from a renal transplant recipient with cytomegalovirus infection was performed. A small but clearly distinguishable subpopulation of CD4dullCD8bright 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. CD4dullCD8bright double-positive T-lymphocytes are enriched for memory and effector cytotoxic T cells.