CXCR4 and infection: At day 12 after infection, culture supernatants were used to infect either a pure population of GHOST-CD4/CCR5 or GHOST-CD4/CXCR4 cells, and a 80:20 mixture of GHOST-CD4/CCR8:GHOST-CD4/CCR5 and GHOST-CD4/CCR8:GHOST-CD4/CXCR4.