Interferon-gamma (IFNÃŽ³) is a dimerized soluble cytokine and the only member of the type II class of interferons. IFNÃŽ³ plays a critical role in innate and adaptive immunity against viral, some bacterial, and protozoal infections. IFNÃŽ³ activates macrophages, induces MHC class II expression, targets virus-infected cells, and inhibits viral replication directly. IFNÃŽ³ can also regulate the functions of many immune cells, including T cells and macrophages. IFNÃŽ³ is produced by activated CD4 (Th1) cells,CD8 CTLs, NK, and NKT cells. IFN-γ can also upregulate MHC class I and II antigen expression in antigen-presenting cells