CXCL8 and HIV infectious disease: Our studies have shown that morphine at concentrations of 10−7 M (P < 0.01), 10−9 M, 10−11 M significantly decreased the IL-8 expression in U87 astrocytoma cell lines by 29% (P < 0.01), 47% (P < 0.01), and 68% (P < 0.05), respectively (Figure 2), suggesting that morphine acts as a cofactor for the HIV infection leading to a significant down-regulation of IL-8 gene expression in a dose-dependent manner.