CXCR4 and infection: The more prolonged period of viremia for scSIVmac155T3 TMstop was significant based on area under the curve comparisons with scSIVmac239 TMstop and scSIVmac316 TMstop[32], and may reflect preferential infection of a CD4+CXCR4+ target cell population that is less susceptible to the cytopathic effects of infection or more resistant to clearance by virus-specific immune responses.