|Detection of ICOS in Human CD3+ PBMCs by Flow Cytometry. Human CD3+ peripheral blood mononuclear cells (PBMCs) treated for 48 hours with 5 μg/mL PHA were stained with Mouse Anti-Human ICOS APC‑conjugated Monoclonal Antibody (Catalog # FAB6975A, filled histogram) or isotype control antibody (Catalog # IC002A, open histogram). View our protocol for Staining Membrane-associated Proteins.|
Inducible Costimulator (ICOS), also known as AILIM (Activation-Inducible Lymphocyte Immunomediatory Molecule), CD278, and CRP-1 (CD28-Related Protein-1), is a member of the growing CD28 family of immune costimulatory receptors. Other family members are CD28, CTLA-4, and PD-1. Human ICOS is a homodimeric type I transmembrane protein consisting of 199 amino acids (aa) with a putative 20 aa signal sequence, a 121 aa extracellular domain, a 23 aa transmembrane region, and a 35 aa cytoplasmic domain. ICOS shares approximately 39% amino acid similarity with CD28 and CTLA-4. Over aa 21-141, human and mouse ICOS share approximately 70% aa sequence identity. ICOS is expressed on most CD45RO+ cells. ICOS expression is up-regulated within approximately 24-48 hours of activation on Th primed cells. B7-H2, a member of the B7 family of costimulatory ligands, has been identified as the ICOS ligand. The B7-H2/ICOS interaction appears to play roles in T cell dependent B cell activation and Th differentiation.