CD4(dull)CD8(bright) double-positive T-lymphocytes have a phenotype of granzyme B(pos)CD8(pos) 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 h ave a CD4(bright)CD8(dull) phenotype. CD4(dull)CD8(bright) T-lymphocytes ha ve been found only in temporal association with some viral infections. Methods, Four-colour flow cytometric analysis of peripheral blood mononucle ar cells from a renal transplant recipient with cytomegalovirus infection w as performed. Results. A small but clearly distinguishable subpopulation of CD4(dull)CD8( bright) double-positive T-lymphocytes was detected, that exhibited phenotyp ic characteristics of cytotoxic T-lymphocytes and were granzyme B positive. Furthermore, no naive cells appeared to be present within this subpopulati on. Conclusions. CD4(dull)CD8(bright) double-positive T-lymphocytes are enriche d for memory and effector cytotoxic T cells.