From staining C data it becomes apparent that the increase in CD4+ T helper memory cells in MDD patients was due to a slightly (and not significant) different cell apportioning in CMV seronegative and seropositive patients (Table 4): In seronegative MDD patients T central memory cell frequency was the highest, while in seropositive MDD patients T effector memory cell frequency was the highest. Here, CD4 is linked to major depressive disorder.