Allograft-Inflammatory Factor 1 (AIF-1), also known as Ionized Calcium-Binding Adapter Molecule 1 (Iba1) and Diantain, is a macrophage/microglia-specific calcium-binding protein. Human AIF-1/Iba1 is 147 amino acids (aa) in length with a predicted molecule weight of approximately 17 kDa. This cytoplasmic protein contains two calcium-binding EF hand motifs at aa 45-80 and 81-115. Alternative splicing produces a second isoform, which lacks the first 54 N-terminal aa, and a third isoform that lacks aa 1-54, as well as aa 121-147, but also has a 66 aa insertion at position 65. Human AIF-1/Iba1 shares 89% aa sequence identity with the mouse and rat orthologs. AIF-1/Iba1 expression in macrophages and microglia is upregulated during the activation of these cells. It is important for the proinflammatory response to ischemia, tissue injury, and atherosclerosis. AIF-1/Iba1 is also expressed in vascular smooth muscle and endothelial cells, where it promotes vascular remodeling and new vessel formation. Additionally, AIF-1/Iba1 is upregulated in allografted tissue during transplant rejection, and promotes the proliferation of breast cancer cells and in vivo tumorigenesis.