Since, tropomyosin alpha-4 isoform 1, pyruvate kinase isozymes M1/M2, ER ATPase, and STIP-1 were down-regulated in HIV-1 and HIV-1/HCV infection but not in HCV-infected PBMC, their down-regulation is likely related to the presence of HIV-1 infection. The gene discussed is STIP1; the disease is HIV-1 infection.