Nitric oxide (NO) has been shown to be important for intracellular microbiostasis in vitro. To determine the role of NO in immune function in vivo, groups of C57BL/6 mice were given a sublethal intravenous inoculum of Listeria monocytogenes EGD, and their urine was monitored daily for nitrate, the mammalian end product of NO metabolism. Urinary nitrate levels peaked at 5 to 10 times the basal level on days 5 to 6, when spleen and liver Listeria counts declined most steeply, and decreased thereafter, when spleens and livers were nearly sterile. Peritoneal macrophages explanted from Listeria-infected mice produced nitrite spontaneously, whereas macrophages from uninfected mice did not. The inducible NO synthase mRNA was detectable in the spleens of infected mice on days 1 to 4 of infection. When Listeria-infected mice were treated orally throughout the infection with N`'-monomethyl-L-arginine (NMMA), a specific NO synthase inhibitor, they showed no detectable rise in urinary nitrate excretion. Mean Listeria counts in the livers and spleens of NMMA-treated mice were 1 to 3 orders of magnitude greater than counts in control mice on days 4 through 8 of infection. Compared with control mice, NMMA-treated mice also showed worse clinical signs of infection, namely, weight loss, hypothermia, decreased food and water intake, and decreased urine output. Histologically, NMMAtreated mice had many more inflammatory foci in their livers and spleens than control mice. The histologic observation that mononuclear cells are present at sites of infection suggests that inhibiting NO production did not block the flux of macrophages into infected viscera. As controls for possible drug toxicity, a group of uninfected mice given NMMA orally showed no detrimental effects on weight, temperature, and food and water intake. These experiments demonstrate that inhibition of NO production in Listeria-infected mice results in an exacerbated infection and thus that NO synthesis is important for immune defense against Listeria infection in mice.

Mice infected with Listeria monocytogenes (LM) generate H2-M3wt-restricted CD8 effectors which recognize a heat-killed LM-associated antigen (HAA) presented by macrophages. To characterize HAA, we extracted a bioactive component from LM using SDS or NaOH. Extracted HAA aggregated in hydrophilic solvents but dissociated in the presence of SDS into a smaller subunit which migrated in Sephadex G-200 between chymotrypsinogen (25 kDa) and cytochrome c (12.5 kDa). HAA bioactivity and size was unaffected by proteinase K under conditions which degraded virtually all detectable protein. HAA was also unaffected by other proteases, RNase and DNase, but HAA bioactivity was destroyed by periodate, an agent that degrades carbohydrates. These studies demonstrate that H2-M3wt can present a hydrophobic, non-peptide, microbial antigen, probably glycolipid in origin, to CD8 T cells.

Automated in ovo vaccination is an efficient method for mass immunization of poultry. Although in ovo vaccination has been used to mass immunize chickens against several infectious diseases, there are common poultry diseases for which in ovo-compatible vaccines are not commercially available. It was recently demonstrated that in ovo administration of a nonreplicating human adenovirus vector encoding an avian influenza virus hemagglutinin induced protective immunity against highly pathogenic avian influenza. The advantages of this new class of poultry vaccine include in ovo delivery of a wide variety of pathogen-derived antigens, high potency in a single-dose regimen, rapid production in response to increased demand, no replication of the vector, no pre-existing immunity to human adenovirus in chickens, compatibility with automated in ovo administration and no interference with epidemiological surveys of natural infections.

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SUMMARYCytotoxic T lymphocytes (CTL) recognize and lyse target cells through the interaction of the T-cell receptor complex with the class I or class II major histocompatibility complex (MHC). The production of class I-restricted CTL has been shown to be critical to the elimination of specific pathogens including Listeria monocytogenes. However, the function of class II-restricted CTL in the clearance of intracellular pathogens is poorly understood. H-2 b b2 -microglobulin-deficient mice (b 2 Mÿ/ÿ) are not able to produce CD8 CTL in response to infection with L. monocytogenes. We used this model to evaluate the efficacy of class II-restricted CTL, in the absence of a class I-restricted response, during a primary infection with L. monocytogenes. We demonstrate that, despite their effectiveness in adoptive transfer of protection, Listeria-specific CD4 class II-restricted cytotoxic lymphocytes are ineffective in decreasing titres of L. monocytogenes in the spleen after an established infection. In b 2 Mÿ/ÿ mice, persistence of L. monocytogenes in the spleen was found preferentially in class II-negative cells. Surprisingly, class Irestricted CTL from C57BL/6 mice were capable of decreasing bacterial titres during an established infection even in the absence of detectable class I on the surface of cells from b 2 Mÿ/ÿ mice. These data strongly suggest that, in the absence of a class I-restricted response, pathogens that elicit a class IIrestricted cytotoxic response may escape prompt eradication by the immune system.