ICAM-1 is a member of the immunoglobulin superfamily, the superfamily of proteins including antibodies and T-cell receptors. The structure of ICAM-1 is characterized by heavy glycosylation, and the protein’s extracellular domain is composed of multiple loops created by disulfide bridges within the protein. ICAM-1 can be induced by interleukin-1 (IL-1) and tumor necrosis factor (TNF) and is expressed by the vascular endothelium, macrophages, and lymphocytes. ICAM-1 is a ligand for LFA-1 (integrin), a receptor found on leukocytes. More recently, ICAM-1 has been characterized as a site for the cellular entry of human rhinovirus. ICAM-1 and soluble ICAM-1 have antagonistic effects on the tight junctions forming the blood-testis barrier, thus playing a major role in spermatogenesis. ICAM-1 has been implicated in subarachnoid hemorrhage (SAH). Levels of ICAM-1 are shown to be significantly elevated in patients with SAH over control subjects in many studies.