CXCR5 and infection: Therefore, even though the distinct patterns of expression of the two chemokine receptors CCR5 and CXCR5 align with the cellular versus humoral arms of the CD4+ T cell immune response, there appears to be some limited cellular overlap of expression during differentiation which accounts for the observed paradoxical combination of simultaneous accumulation and infection of Tfh during SIV and HIV-1 chronic infections.