IFNG and infection: Regarding CD4+ T cells, it has been known for decades from studies of recurrent herpes that CD4+ T cells infiltrate early during infection (12–48 h) [45] and their interferon (IFN)-γ production is important for combating infection in keratinocytes, reversing MHC class I downregulation [46], and for attracting CD8+ T cells to the site of the infection [136].