Lipoglycans from mycoplasmas

Lipoglycans , distinguishable from bacterial lipopolysaccharides, are associated with the cytoplasmic membranes of several genera of Mollicutes, namely Acholeplasma, Mycoplasma neurolyticum , Anaeroplasma , and Thermoplasma. Structurally, the lipoglycans are long heteropolysaccharides covalently linked to a lipid. The exact structures of three have been determined. Thermoplasma oligosaccharide is attached to a diglycerol tetraether ; A. granularum to a diacyl glycerol. The lipoglycan from A. axanthum is unique by its possession of glycerol phosphate and galactose phosphate side chains and the occurrence of fatty acids in N-acyl linkages. Only one molecular species of lipoglycan occurs in a given species. These lipoglycans possess a variety of biological activities. The terminal three sugar residues define their antigenic specificity; they attach to specific receptors on mammalian cells; they exhibit pyrogenicity in rabbits and clot Limulus lysate; they stimulate the production of IgM antibody both in vivo and in vitro; they modulate the immune response to T-cell dependent antigens; they exhibit immunosuppressive and immunostimulatory activities.