A series of studies performed in the mouse model revealed that monocytes, CD4 T cells, and CD8 T cells played a role in preventing RVFV-mediated encephalitis in the context of an active innate immune response, and that B cells contributed to viral clearance.12,13 These key findings suggested that T cells may be involved in modulating RVFV disease, and are further supported by the discovery that HIV-positive patients infected with RVFV had increased case fatality rates and increased occurrence of CNS manifestations of disease.14,15. This evidence concerns the gene CD4 and encephalitis.