CXCR4 and viral infectious disease: For CXCR4+ cells in both naïve and memory compartments, a two-fold reduction in peak labelling was also noted (Figure S2C, S2D), even though this patient had a predominantly R5-tropic circulating strain of virus, suggesting that the proliferation-inducing effects of HIV infection in this subject were not due to cellular tropism directed, subset-specific effects of viral infection.