Synthesis of ß-arabinofuranoside glycolipids, studies of their binding to surfactant protein-A and effect on sliding motilities of M. smegmatis.

Surfactant protein A (SP-A), which is a lung innate immune system component, is known to bind glycolipids present at the cell surface of a mycobacterial pathogen. Lipoarabinomannan (LAM), a component of mycobacterial thick, waxy cell wall, is one of the glycolipid ligands for SP-A. In order to assess binding of synthetic glycolipids with SP-A and the glycosidic linkage preferences for the interaction, ß-arabinofuranoside trisaccharide glycolipids constituted with ß-(1→2), ß-(1→3) and ß-(1→2), ß-(1→5) linkages relevant to LAM were synthesized through chemical glycosylations. The efficacies of synthetic glycolipids to interact with SP-A were assessed by using the surface plasmon resonance (SPR) technique, from which association-dissociation rate constants and equilibrium binding constants were derived. The equilibrium binding constants of the interaction of two constitutionally varying ß-arabinofuranoside glycolipids with SP-A were found to be in the millimolar range. A comparison of the results with few α-anomeric arabinofuranoside glycolipids showed that glycolipids with ß-anomeric linkages were having relatively lower equilibrium binding constants than those with α-anomeric linkages in binding to the protein, whereas oligosaccharides alone, without lipidic chains, exhibited higher equilibrium binding constants. Further, the synthetic compounds inhibited the growth of mycobacteria and affected sliding motilities of the bacteria, although to an extent relatively lesser than that of synthetic compounds constituted with α-anomeric linkages.

Early IL-4 induction in bone marrow lymphoid precursor cells by mycobacterial lipoarabinomannan.

IL-4 is produced promptly in response to certain infections and plays a key role in the Th1/Th2 T cell dichotomy; however, the cellular source remains a matter of debate. Here we describe the induction of IL-4 in bone marrow cells of normal and RAG-/- mice by both Mycobacterium tuberculosis and its major cell wall glycolipid, lipoarabinomannan. Characterization of the cell type responsible indicated that it was distinct from the NK1+ or CD4+ T cell previously ascribed the function of rapid IL-4 secretion. Cell-sorting experiments identified CD19+/B220+ precursor cells, presumably pre-B cells that produced IL-4 constitutively and whose frequency was rapidly and markedly up-regulated by lipoarabinomannan. Thus, pathogenic mycobacteria and their glycolipids may influence hemopoiesis by rapidly inducing IL-4 secretion in the bone marrow.

The isolation of anti-gum arabic antibodies by affinity chromatography.

Antibodies directed at gum arabic have been induced in rabbits immunized with gum arabic in Freund's complete adjuvant. These antibodies have been isolated in pure form by affinity chromatography on AH-Sepharose 4B containing gum arabic ligands. Oxidation of the susceptable carbohydrate residues of gum arabic with periodate or reduction of the glucuronic acid moieties with carbodiimide and borohydride converted the polysaccharide to products which no longer yielded precipitin reactions with the antibodies. The antibodies are therefore anti-carbohydrate antibodies with specificity for certain carbohydrate units of the gum arabic. Results of chemical modification and inhibition experiments indicate that 4-alpha-L-arabinofuranosyl-D-glucuronic acid units of the polysaccharide are the major immunodeterminant groups.