The majority of in vitro studies have shown that morphine enhances HIV infection of PBMC (Suzuki et al., 2002), CD4+ T cells (Chuang et al., 1993; Steele et al., 2003; Peterson et al., 2004), and macrophages (Guo et al., 2002; Li et al., 2002, 2003; Ho et al., 2003; Wang et al., 2011a, 2012). This evidence concerns the gene CD4 and HIV infectious disease.