The RGD peptide is the binding motif of fibronectin to cell adhesion molecules. RGD peptide acts as an inhibitor of integrin-ligand interactions and can induce apoptosis in the absence of signals and integrin-mediated cell clustering. The RGDS sequence was found initially to promote the attachment of rat kidney fibroblasts to fibronectin. The free RGDS peptide inhibits attachment of cells to fibronectin-coated substrates. The RGDS sequence is also a target for infectious agents (Treponema's syphilis, Mycobacterium's tuberculosis). RGDS can also block fibrinogen-induced aggregation of intact erythrocytes and specific binding of fibrinogen to erythrocyte membranes.