CD61 is a cluster of differentiation found on thrombocytes. The ITGB3 protein product is the integrin beta chain beta 3. Integrins are integral cell-surface proteins composed of an alpha chain and a beta chain. A given chain may combine with multiple partners resulting in different integrins. Integrin beta 3 is found along with the alpha IIb chain in platelets. Integrins are known to participate in cell adhesion as well as cell-surface mediated signalling.

The platelet and endothelial cell heterodimers use GP IIIa as the beta subunit; the leukocyte heterodimers contain a beta subunit with a molecular mass of 95 kD that is homologous to GP IIIa but is clearly a different protein; and the fibronectin receptors contain a beta subunit that appears to be analogous to band 3 of integrin.