However, while alternative entry pathways are used in vivo in nonpathogenic infection of sooty mangabey and red-capped mangabey natural hosts [29,30], it is unclear whether any of these pathways, including GPR15 and CXCR6, play a role in SIVmac infection of rhesus macaques [21,22], and there appears to be no consequence in vivo to loss of GPR15 utilization [22]. Here, GPR15 is linked to infection.