**5.1 Summary of gliosis**

The overall response to SIV or HIV infection of the CNS which primarily involves infected monocyte/macrophages is pro-inflammatory. Neuroinvasion by monocyte/macrophages initiates a positive feedback loop stimulating glial cells to respond further. Glial involvement increases not only the intensity but the area affected by inflammation, damaging local neural circuitry, and recruiting monocytes into the parenchyma. While the glial inflammatory response may seem detrimental, ablation of monocytes led to increased tissue damage in a model of retinal inflammation, implicating lesion formation as a partially neuroprotective response (London et al., 2011). Although the initial monocytes entering the brain carrying HIV/SIV may not be recruited by glial signaling, later neuroinvasion is likely driven, at least in part, by gliosis.
