Our findings indicate that heparin can selectively inhibit the productive infection of FIV TCA, but not FIV FS, which is consistent with the report that polyanions (such as heparin and dextran sulfate) selectively inhibit HIV infection of CXCR4+ or CCR5+/CXCR4+ cells, but not CXCR4-/CCR5+ cells [36]. This evidence concerns the gene CCR5 and HIV infectious disease.