We further examined the population of peripheral monocyte/macrophages (CD45hiCD11b+ Ly6G-) and brain resident microglia (CD45loCD11b+) at day 5 p.i. The analysis revealed a significant increase in the numbers of peripheral monocyte/macrophages as well as brain resident microglia in WT mice upon infection, but interestingly no significant alterations were observed in CD40L-/- mice, compared to their corresponding MI (Fig 4C and 4D). The gene discussed is CD40LG; the disease is infection.