Soluble bacterial constituents down-regulate secretion of IL-12 in response to intact Gram-positive bacteria.
Intact Gram-positive bacteria induce production of large amounts of IL-12 from freshly isolated human monocytes. Here the bacterial structures and signalling pathways involved were studied and compared with those leading to IL-6 production, and to IL-12 production in response to LPS after IFN-gamma pre-treatment. Intact bifidobacteria induced massive production of IL-12 (1 ng/ml) and IL-6 (>30 ng/ml) from human PBMC, whereas fragmented bifidobacteria induced IL-6, but no IL-12. IL-12 production induced by intact bifidobacteria was inhibited by pre-treatment with bifidobacterial sonicate, peptidoglycan, muramyl dipeptide, lipoteichoic acid, the soluble TLR2 agonist Pam(3)Cys-SK(4), or anti-TLR2 antibodies. Blocking of phagocytosis by cytochalasin, inhibition of the JNK or NF-kappaB pathways or treatment with Wortmannin also reduced the IL-12 response to intact Gram-positive bacteria. LPS induced moderate levels of IL-12 (0.31 ng/ml), but only from IFN-gamma pre-treated PBMC. This IL-12 production was enhanced by Wortmannin and unaffected by blocking the JNK pathway. Thus, intact Gram-positive bacteria trigger monocyte production of large amounts of IL-12 via a distinct pathway that is turned off by fragmented Gram-positive bacteria. This may be a physiological feedback, since such fragments may signal that further activation of the phagocyte via the IL-12/IFN-gamma loop is unnecessary.
Barkman
Cecilia
C
Department of Clinical Bacteriology, University of Gothenburg, Guldhedsgatan 10, SE-413 46 Göteborg, Sweden. cecilia.barkman@microbio.gu.se
Martner
Anna
A
Hessle
Christina
C
Wold
Agnes E
AE
D000119:Acetylmuramyl-Alanyl-Isoglutamine / Q000276:immunology / Q000302:isolation & purification; D000906:Antibodies / Q000276:immunology; D001644:Bifidobacterium / Q000737:chemistry* / Q000276:immunology*; D002478:Cells, Cultured; D006801:Humans; D018664:Interleukin-12 / Q000378:metabolism*; D015850:Interleukin-6 / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000276:immunology*; D055666:Lipopeptides / Q000276:immunology; D008070:Lipopolysaccharides / Q000276:immunology / Q000302:isolation & purification; D010457:Peptidoglycan / Q000276:immunology / Q000302:isolation & purification; D013682:Teichoic Acids / Q000276:immunology / Q000302:isolation & purification
D000906:Antibodies; D015850:Interleukin-6; D055666:Lipopeptides; D008070:Lipopolysaccharides; C508075:Pam(3)CSK(4) peptide; D010457:Peptidoglycan; D013682:Teichoic Acids; D018664:Interleukin-12; D000119:Acetylmuramyl-Alanyl-Isoglutamine; C009900:lipoteichoic acid