Expression of CXCR1 in CD8⁺ T cells. After permeabilization, CD8⁺ T cells were double-labeled for CXCR1 and each perforin, RANTES, GM130, β2MG, CD63, and EEA1. In addition, cells were double labeled for perforin and RANTES. Similar to perforin and RANTES, CXCR1 staining was granular, and no colocalization of CXCR1 with either perforin or RANTES was observed. Perforin^low/neg CD8⁺ T cells tended to express more CXCR1 (i) than did perforin^high CD8⁺ T cells (ii). Indicative of ongoing low-level sorting of CXCR1 into the constitutive secretory pathway and its endocytic reuptake, some distinct colocalization of CXCR1 with GM130 (Golgi), β₂-microglobulin (constitutive secretory pathway), and EEA1 (early endosomal compartment) was observed in a subset of cells (bottom row). No staining was seen when incubating permeabilized CD8⁺ T cells with appropriate isotype-control antibodies (data not shown).