Lack of productive infection is consistent with failure to detect expression of the HIV-1 receptor CD4 on primary astrocytes and immortalized lines (Boutet et al., 2001, Ma et al., 1994, Peudenier et al., 1991, Sabri et al., 1999, Willey et al., 2003) and lack of consensus regarding CCR5 or CXCR4 expression (Rezaie et al., 2002, Sabri et al., 1999, Willey et al., 2003). This evidence concerns the gene CXCR4 and infection.