In humans, the proportion of CD4+ T-cells that also express CCR5 varies according to tissue source and inflamation; approximately 5–10% of peripheral blood CD4+ T-cells express CCR5, while most gut associated lymphoid tissue and rheumatoid arthritis synovial fluid CD4+ T-cells are CCR5+ (Agace et al., 2000; Qin et al., 1998). The gene discussed is CD4; the disease is rheumatoid arthritis.