CD4 and infection: Lin et al used transgenic mice, called “macrophages insensitive to interferon-γ” mice to assess the effects of IFN-γ signaling on macrophage lineage cells in response to infection of lymphocytic choriomeningitis virus, they reported that CD4+ T-cell production of IFN-γ promotes signaling in macrophage lineage cells, which control the production of chemokines i.e., MCP-1, and the recruitment of macrophages to the central neuron system [31].