Role of acyl residues in polyclonal murine B cell activation by acylpoly(1,3)galactosides from Klebsiella pneumoniae.
Several components of Klebsiella pneumoniae including a membrane proteoglycan (Kp-MPG) were reported to activate macrophages and to induce T-independent polyclonal activation of mouse B cells. Chemically defined derivatives of Kp-MPG were prepared and characterized, enabling us to approach the molecular substructures involved in the binding to lymphocytes and the activation of B cells. Five derivatives were characterized: (i) an acylpoly(1,3)galactoside containing ester-linked fatty acids (EFA-APG) which was obtained by mild alkaline hydrolysis, (ii) a polymer of EFA-APG (APG pol1), (iii) a preparation obtained by drastic alkaline hydrolysis and delipidation which removed the esterified fatty acids (APG), (iv) a polymer of the latter compound (APG pol2), and (v) an APG preparation submitted to mild acid hydrolysis which removed all fatty acids but left the galactose chain of APG (GC-APG) intact. The derivatives were studied for their capacity to bind to and to activate mouse splenocytes. Binding was investigated on BALB/c and C3H/HeJ splenocytes by indirect immunofluorescence using biotinylated F(ab')2 of anti-Kp-MPG antibodies and the streptavidin-phycoerythrin amplification system in flow cytometry and by competition of unlabeled APG with biotinylated APG. Activation was studied by measuring (i) [3H]thymidine incorporation into spleen cells from BALB/c, C3H/HeJ, nude (nu+/nu+) mouse strains, and purified B cells of BALB/c; (ii) immunoglobulin secretion in culture supernatants; and (iii) blastogenesis. The results demonstrate a specific uptake of EFA-APG and APG by T cells as well as by B cells and exclude a contribution of the polygalactose part of the APG molecule (GC-APG) to the binding to spleen lymphocytes. Unlike LPS from the same strain of K. pneumoniae, APG pol1 stimulated B cell activation in the LPS-resistant C3H/HeJ strain as well as in BALB/c mice. The compounds did not activate T cells and were T-independent B cell activators, stimulating nu+/nu+ spleen cells and inducing primarily IgM and IgG3 synthesis. Polymers were more potent activators than monomers and removal of ester-linked fatty acids completely abrogated B cell-activating properties. The monomer APG antagonized B cell activation by Kp-MPG, LPS from K. pneumoniae, and APG pol1. The data indicate that within the EFA-APG molecule, distinct substructures are required for binding and for triggering B cell response.
Hmama
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Laboratoire d'Immunologie, INSERM U80 CNRS URA 1177 UCBL, Hôpital E. Herriot, Lyon, France.
Lina
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Normier
G
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Binz
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Revillard
J P
JP
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D005697:Galactosides / Q000494:pharmacology*; D007711:Klebsiella pneumoniae / Q000737:chemistry*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D011509:Proteoglycans / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000502:physiology
D005697:Galactosides; D008070:Lipopolysaccharides; D011509:Proteoglycans