INDUCTION OF NITRIC-OXIDE SYNTHESIS AND XANTHINE-OXIDASE AND THEIR ROLES IN THE ANTIMICROBIAL MECHANISM AGAINST SALMONELLA-TYPHIMURIUM INFECTION IN MICE

The role of superoxide anion (O-2(-)) and nitric oxide (NO) in the hos t defense mechanism against Salmonella typhimurium (LT-2) was examined by focusing on xanthine oxidase (XO) as an O-2(-)-generating system a nd on inducible NO synthase (iNOS). When ICR mice were infected with a 0.1 50% lethal dose (2 x 10(5) CFU) of S. typhimurium, bacterial grow th in the liver reached a peak value 3 days after infection (10(4.32) CFU/g of liver) and decreased thereafter. XO activity in the liver bec ame maximum at 7 days after infection; the value was 34.6 +/- 1.4 mU/g of liver at 7 days (compared with 11.0 +/- 1.3 mU/g of liver before i nfection), The time profile of NO production in the liver as determine d by electron spin resonance spectroscopy was consistent with that of XO activity. Histological examination of infected liver shelved the fo rmation of multiple microabscesses with granulomatous lesions consisti ng of polymorphonuclear cells and mononuclear cells, and iNOS expressi ng cells were localized in the confined areas of the microabscesses. W hen XO inhibitors such as allopurinol and 4-amino-6-hydroxypyrazolo[3, 4-d]pyrimidine (AHPP) were administered to the infected mice, the mort ality of the mice was significantly increased (10 of 21 and 11 of 20 f or the allopurinol- and AHPP treated groups, respectively, versus 2 of 20 for control mice), and bacterial growth was significantly enhanced , A similar exacerbation of the infection was obtained with N-omega-mo nomethyl-L-arginine (L-NMMA) treatment of the mice. Of considerable im portance is that granuloma formation in tile liver was poorly develope d by treatment with either XO inhibitors or L-NMMA. These results sugg est that XO and NO play an important role in the antimicrobial mechani sm against S. typhimurium in mice.