IL7 and HIV-1 infection: Increased IL-7 levels in progressive HIV-1 infection may also increase the expression of the coreceptor CXCR4, resulting in a greater risk of emergence of an X4-using viral strain [69], and in turn IL-7 may prove to be more deleterious and pro-apoptogenic with these X4 viral strains, as it causes an increase of Fas [70-72].