CD4 and infection: Other possible entry mechanisms for WNV include (i) infection or passive transport through choroid plexus epithelial cells [62], (ii) a “Trojan horse” mechanism in which the virus is transported by infected immune cells (e.g., neutrophils [34] or CD4+ or CD8+ T cells [63]) that cross the BBB [64], (iii) infection of olfactory neurons and rostral spread from the olfactory bulb [65], or (iv) direct infection of brain microvascular endothelial cells [66].