Role of porin of Shigella dysenteriae type 1 in modulation of lipopolysaccharide mediated nitric oxide and interleukin-1 release by murine peritonealmacrophages

The ability of Shigella dysenteriae type 1 porin to induce the release of n itric oxide (NO) and interleukin-l (IL-1) from peritoneal macrophages of mo use and to regulate lipopolysaccharide (LPS) and gamma interferon (IFN-gamm a) mediated release of the two proinflammatory mediators was investigated. Porin released nitrite when added to macrophage cultures. A maximum of 3.2- fold nitrite release by macrophages was observed with 100 ng ml(-1) of pori n. The nitrite release of LPS was enhanced significantly by lower concentra tions of porin, whereas the effect of IFN-gamma was enhanced by porin at hi gher concentrations. Polysaccharide (PS) moiety of LPS stimulated the nitri te release of elicited macrophages by 1.6-fold compared to untreated contro l. It also enhanced the stimulatory effect of 1 and 10 ng ml(-1) of porin b y 1.3-fold. Lipid A (LPA) moiety of LPS did not release nitrite, nor did it increase the porin mediated nitrite production. Porin treated 24 h old mac rophage culture supernatants were applied for ConA activated thymocyte prol iferation as a measure for determination of IL-I release. Sixty percent dep letion of thymocyte proliferation was;observed when the porin treated macro phage supernatants were absorbed with anti-IL-l antibody. A maximum of 5.5- fold increase of thymocyte proliferation over control was found with 1 and 10 ng ml(-1) of porin. One or 10 ng ml(-1) of porin and LPS augmented the t hymocyte growth, 1.5-fold beyond that obtained by porin and 1.8-/1.7-fold m ore than that obtained by LPS, alone. Similarly, porin and IFN-gamma co-sti mulated the cell growth also. PS enhanced the thymocyte proliferation by 5- fold. It also enhanced the thymocyte growth by co-stimulating 1.4-fold the effect observed by 1 or 10 ng ml(-1) of porin alone. LPA could not particip ate in the cell proliferating activity nor did it enhance the stimulatory e ffect of porin. Therefore, both nitrite release and thymocyte proliferation by LPS could be substituted by PS only. The tight association of the two b acterial outer membrane components, porin and LPS, could be a necessary co- signal for boosting the release of the two proinflammatory mediators, namel y NO and IL-1, which may be associated with the inflammatory response of th e colon during Shigella invasion. (C) 2000 Federation of European Microbiol ogical Societies. Published by Elsevier Science B.V. All rights reserved.