| Part I. Lipid A is the causative agent of Gram-negative sepsis, a leading cause of mortality among hospitalized patients. Compounds that bind lipid A can limit its detrimental effects. To better understand interactions of lipid A and lipid A binding agents, lipid A derivatives were prepared with incrementally varied lipid chain lengths. These lipid A derivatives were used to study their interactions with polymyxins and cationic steroid antibiotics using isothermal titration calorimetry and fluorescence spectroscopy, respectively. To develop cationic steroid antibiotics with high affinities for lipid A, combinatorial methods were used and fluorophore appended lipid A derivatives were prepared as probes for "on-bead" screening.; Part II. Natural killer T cells (NKT cells) are a subpopulation of T cells that control multiple immune responses including autoimmunity, antitumor, and allergic activities. In response to stimulation caused by glycolipids presented by CD1d, NKT cells are capable of rapidly producing a variety of cytokines to exert significant controls on the broader T-cell pool. To search for the natural ligand(s) of CD1d presentation and NKT cell stimulation, three sequences of glycosphingolipids were prepared as candidates: (1) 3″-O-sulfo-glycosylceramides; (2) globosides and isoglobosides; (3) alpha-uronosylceramides from LPS-negative Gram-negative bacteria Sphingomonas capsulata. Among these glycosylceramides, iGb3 was identified as an endogenous antigen of CD1d restricted NKT cells. Our findings also suggested that bacteria Sphingomonas capsulata were directly detected by NKT cells through specific recognition of alpha-uronosylceramides in bacterial cell walls. |
