Host macrophages were replaced with donor-derived cells during the course of immune reconstitution. (A) CCR5-expressing macrophages were detected by in situ immunofluorescence double staining for CD68 (green) and CCR5 (red) in colon tissue sections obtained 5.5 or 24 months after CCR5Δ32/Δ32 SCT. CCR5-expressing macrophages are indicated by yellow arrows. (B) At 24 and 29 months after CCR5Δ32/Δ32 SCT, macrophages were sorted from mucosal cells and genotyped by CCR5 variant-specific PCR.