ICAM-1 (Intercellular Adhesion Molecule 1) also known as CD54 is a protein that in humans is encoded by the ICAM1 gene. This gene encodes a cell surface glycoprotein which is typically expressed on endothelial cells and cells of the immune system.

The protein encoded by this gene is a type of intercellular adhesion molecule continuously present in low concentrations in the membranes of leukocytes and endothelial cells. Upon cytokine stimulation, the concentrations greatly increase. 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. When activated, leukocytes bind to endothelial cells via ICAM-1/LFA-1 and then transmigrate into tissues. LFA-1 has also been found in a soluble form, which seems to bind and block ICAM-1.

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. While ICAM-1 has not been shown to be directly correlated with cerebral vasospasm, a secondary symptom that affects 70% of SAH patients, treatment with anti-ICAM-1 reduced the severity of vasospasm. ICAM-1 expressed by respiratory epithelial cells is also the binding site for rhinovirus, the causative agent of most common colds. ICAM-1 has an important role in ocular allergies recruiting pro-inflammatory lymphocytes and mast cells promoting a type I hypersensitivity reaction.