The concept of carbohydrate-to-carbohydrate interaction (CCI) as a basis of cell adhesion was originally developed during (i) our studies on mechanism of autoaggregation of mouse teratocarcinoma F9 cells, which mimics compaction of pre-implantation embryo; and (ii) studies by Max Burger and his group on species-specific autoaggregation of marine sponge cells. During the past decade, an increasing variety of structures have been found to be involved in either homotypic or heterotypic CCI, occurring through clusters of glycosphingolipids (GSLs) at the surfaces of two interfacing cells. CCI has been well elaborated by advanced technology in surface plasmon resonance (SPR) spectroscopy and atomic force microscopy, and its binding affinity is in the same range as that of carbohydrate-to-protein interaction (CPI) and protein-to-protein interaction (PPI). CCI has unique features not found in CPI or PPI. The specific aims of the proposed studies are: 1. Explore new cell adhesion systems based on new types of CCI detected using previously untested GSLs, and PE-conjugated N-linked or O-linked oligosaccharide probes from glycoproteins: (a) CCI based on previously-untested GSL structures; (b) CCI based on N-linked or O-linked oligosaccharides, conjugated to PE, assembled as "glycosyl SAM" or "glycochip"; (c) cell adhesion system based on the newly-found CCI. 2. Elucidate and provide evidence for involvement of CCI as initial step in physiologically or pathobiologically relevant cell adhesion systems in which CCI is suggested to occur, (a) Further studies on Lex-based CCI and cadherin-based PPI in mouse teratocarcinoma F9 cell autoaggregation. (b) Other cell adhesion systems: (i) Lex-based cell-to-cell adhesion of contact-inhibited corneal epithelial cells; (ii) Gb4-dependent CCI in autoaggregation of human teratocarcinoma cells; (iii) Ley-to-H interaction mediating adhesion of human cancer cells to endothelial cells; (iv) Mechanism of melanoma cell adhesion to mouse endothelial cells, based on GM3-to-LacCer interaction. Cell adhesion through CCI observed in Project 1 or 2 will be confirmed by (i) ruling out possible involvement of carbohydrate-binding protein; (ii) application of RNAi approach; (iii) a new SPR/ "digital window" procedure.