VEGF is a homodimeric heavily glycosylated protein.The human factor occurs in several molecular variants of 121, 162, 145, 148, 165, 183, 189 , 206 amino acids, arising by alternative splicing of the mRNA.The splice forms of VEGF differ in biological properties such as the receptor types they recognize and their interaction with heparan sulfate proteoglycans. The 165 amino acid form of the factor is the most common form in most tissues. Kaposi sarcomas express VEGF121 and VEGF165. VEGF121 and VEGF165 are soluble secreted forms of the factor while VEGF189 and VEGF206 are mostly bound to heparin-containing proteoglycans in the cell surface or in the basement membrane. A high-affinity glycoprotein receptor of 170-235 kDa is expressed on vascular endothelial cells. The interaction of VEGF with heparin-like molecules of the extracellular matrix is required for efficient receptor binding. The high-affinity receptor for VEGF, now known as VEGFR1, has been identified as the gene product of the FLT-1. Another receptor for VEGF, now known as VEGFR2, is KDR, also known as FLK-1. A third receptor type, VEGFR3 is known also as FLT- 4. An isoform-specific receptor for VEGF165 has been identified as human Neuropilin-1.