AIF1 is a cytoplasmic, calcium-binding protein that is thought to play a role in macrophage activation and function. AIF1, containing two EF domains, is induced by cytokines and Interferons. In an unstimulated state, AIF1 colocalizes with actin, and upon stimulation, translocates to lamellipodia. It is also a marker of human microglia and is expressed by macrophages in injured skeletal muscle. The gene encoding AIF1 resides in the tumor necrosis factor (TNF) cluster of genes, located in the region represented by the human major histocompatibility complex (MHC).