Roles for tumor necrosis factor and gamma interferon in resistance to enteric listeriosis

IFN-Gamma-Dependent and Independent Mechanisms of CD4⁺ Memory T Cell-Mediated Protection from Listeria Infection

While CD8⁺ memory T cells can promote long-lived protection from secondary exposure to intracellular pathogens, less is known regarding the direct protective mechanisms of CD4⁺ T cells. We utilized a prime/boost model in which mice are initially exposed to an acutely infecting strain of lymphocytic choriomeningitis virus (LCMV), followed by a heterologous rechallenge with Listeria monocytogenes recombinantly expressing the MHC Class II-restricted LCMV epitope, GP_61–80 (Lm-gp61). We found that heterologous Lm-gp61 rechallenge resulted in robust activation of CD4⁺ memory T cells and that they were required for rapid bacterial clearance. We further assessed the relative roles of TNF and IFNγ in the direct anti-bacterial function of CD4⁺ memory T cells. We found that disruption of TNF resulted in a complete loss of protection mediated by CD4⁺ memory T cells, whereas disruption of IFNγ signaling to macrophages results in only a partial loss of protection. The protective effect mediated by CD4⁺ T cells corresponded to the rapid accumulation of pro-inflammatory macrophages in the spleen and an altered inflammatory environment in vivo. Overall, we conclude that protection mediated by CD4⁺ memory T cells from heterologous Listeria challenge is most directly dependent on TNF, whereas IFNγ only plays a minor role.

Incidence and nature of infectious disease in patients treated with anti-TNF agents

Tumor necrosis factor alpha (TNF-alpha) inhibitors offer a targeted therapeutic strategy that contrasts with the nonspecific immunosuppressive agents traditionally used to treat most inflammatory diseases. These biologic agents have had a significant impact in ameliorating the signs and symptoms of inflammatory rheumatoid disease and improving patient function. From the onset of clinical trials, a central concern of cytokine blockade has been a potential increase in susceptibility to infections. Not surprisingly, a variety of infections have been reported in association with the use of TNF-alpha inhibitor agents. In particular, there is evidence suggesting an increased rate of granulomatous infections in patients treated with monoclonal TNF-alpha inhibitors. This review provides the incidence and nature of infections in patients treated with TNF-alpha inhibitor agents and reminds the clinician of the required vigilance in monitoring patients.

Regional IFNgamma expression is insufficient for efficacious control of food-borne bacterial pathogens at the gut epithelial barrier

IFNgamma is critical for host defence against various food-borne pathogens including Salmonella enterica and Listeria monocytogenes, the causative agents of salmonellosis and listeriosis, respectively. We investigated the impact of regional IFNgamma expression at the intestinal epithelial barrier on host invasion by salmonellae and listeriae following oral challenge. Transgenic mice (IFNgamma-gut), generated on an IFNgamma knock-out (KO) background, selectively expressed IFNgamma in the gut driven by the modified liver fatty acid-binding protein (Fabpl(4x at -132)) promoter. Infections with attenuated S. enterica Typhimurium or with L. monocytogenes did not differ significantly in IFNgamma-KO, IFNgamma-gut and wild-type mice. Further, Listeria-specific CD4+ and CD8+ T cells were not altered in IFNgamma-gut mice. Thus, this model indicates that local IFNgamma expression by non-immunological cells in the distal part of the small intestine, caecum and colon is insufficient for prevention of gut penetration by S. enterica Typhimurium and L. monocytogenes.

Impact of Biologic Agents on Infectious Diseases

Until recently, inflammatory diseases, collagen vascular diseases, inflammatory bowel diseases, and multiple sclerosis were met with a limited offering for treatment. The introduction of biologic agents has revolutionized the approach to these diseases, offering many patients freedom from disease activity staving off resultant destruction to organs and joints with marked improvement in quality of life and disability. This article focuses on the development of serious infections associated with the use of biologic agents. Presented is a synthesis of case series, reports, and systematic reviews to elucidate implicated pathogens and clinical presentations in patients being treated with biologic agents and to form a cursory backbone for prevention and treatment strategies to which clinicians prescribing these agents or encountering patients already on these agents can readily refer. Maintenance of a high index of suspicion is imperative for the prevention and appropriate treatment of serious life-threatening infections in these patients.

Infections associated with tumor necrosis factor-alpha antagonists

Tumor necrosis factor (TNF)-alpha antagonists are promising therapeutic agents for patients with severe autoimmune and rheumatologic conditions. Unfortunately, their use has been associated with an increased rate of tuberculosis, endemic mycoses, and intracellular bacterial infections. Infliximab, 1 of 3 available drugs in this novel class, appears to be associated with the greatest risk of infection, likely because of its long half-life and induction of monocyte apoptosis. Prospective trials are necessary to determine the exact risk associated with these agents, particularly the newer TNF-alpha antagonists. More specific TNF-alpha blockers, which reduce inflammation while maintaining adequate immunity, are needed. In the meantime, a thorough work-up is mandatory for all febrile illness occurring in TNF-alpha blocker recipients. We present 4 patients who developed severe infections during TNF-alpha antagonist therapy, review the literature, and discuss current guidelines for surveillance and prophylaxis.

Role of flagellin and the two-component CheA/CheY system of Listeria monocytogenes in host cell invasion and virulence

The flagellum protein flagellin of Listeria monocytogenes is encoded by the flaA gene. Immediately downstream of flaA, two genes, cheY and cheA, encoding products with homology to chemotaxis proteins of other bacteria, are located. In this study we constructed deletion mutants with mutations in flaA. cheY, and cheA to elucidate their role in the biology of infection with L. monocytogenes. The DeltacheY, DeltacheA, and double-mutant DeltacheYA mutants, but not DeltaflaA mutant, were motile in liquid media. However, the DeltacheA mutant had impaired swarming and the DeltacheY and DeltacheYA mutants were unable to swarm on soft agar plates, suggesting that cheY and cheA genes encode proteins involved in chemotaxis. The DeltaflaA, DeltacheY, DeltacheA, and DeltacheYA mutants (grown at 24 degrees C) showed reduced association with and invasion of Caco-2 cells compared to the wild-type strain. However, spleens from intragastrically infected BALB/c and C57BL/6 mice showed larger and similar numbers of the DeltaflaA and DeltacheYA mutants, respectively, compared to the wild-type controls. Such a discrepancy could be explained by the fact that tumor necrosis factor receptor p55 deficient mice showed dramatically exacerbated susceptibility to the wild-type but unchanged or only slightly increased levels of the DeltaflaA or DeltacheYA mutant. In summary, we show that listerial flaA. cheY, and cheA gene products facilitate the initial contact with epithelial cells and contribute to effective invasion but that flaA could also be involved in the triggering of immune responses.

Early translocation of acid-adapted Listeria monocytogenes during enteric infection in TNF/LTalpha-/- mice

TNF/LTalpha deficient mice are devoid of Peyer's patches and lack mesenteric lymph nodes. Translocation, especially in the early steps after intragastric delivery of Listeria monocytogenes, has been explored in this study, and the role of TNFalpha has been addressed. We showed that L. monocytogenes translocation occurred at least as efficiently in TNF/LTalpha-/- mice as in TNF/LTalpha+/+ littermates. Even very low inocula (2.7x10(4) cfu) could initiate infection in the TNF/LTalpha deficient mice. Early kinetics of dissemination to the spleen and liver were similar, L. monocytogenes reaching these organs at 8 h post inoculation. However, a 10-fold higher bacterial load was observed at this early time point in the TNF/LTalpha deficient mice. rTNF pretreatment (4 h before intragastric inoculation) had no effect on the L. monocytogenes associated with the caecum-colon walls at 10 h after inoculation, although bacterial levels in the caecum-colon lumen and in spleen and liver were already controlled.

Saccharomyces boulardii stimulates sIgA production and the phagocytic system of gnotobiotic mice

The effect of Saccharomyces boulardii on the immune system was evaluated, comparing germ-free Swiss/NIH mice monoassociated with the probiotic with germ-free mice. Saccharomyces boulardii colonized the gut of germ-free mice and survived the gastrointestinal conditions. An increase in sIgA production, both total and anti-S. boulardii, was observed in the intestinal contents of monoassociated mice when compared with germ-free controls. The number of Kupffer cells was significantly higher in monoassociated mice than in germ-free controls. In S. boulardii-monoassociated mice, clearance of Escherichia coli B41 was higher than in germ-free controls. TNF-alpha, IFN-gamma and IL-12 serum levels were higher at earlier time points in monoassociated mice when compared with germ-free mice. These results show that the yeast S. boulardii modulates the host immune responses. This effect may be of interest for improving the resistance to enteropathogenic bacterial infections.

Roles of endogenous cytokines in liver apoptosis of mice in lethal Listeria monocytogenes infection

Various bacterial pathogens have been identified as mediators of apoptosis. Apoptosis reportedly shows both detrimental and beneficial effects on biological functions. We studied the role of liver apoptosis in lethal Listeria monocytogenes infection and the regulation of apoptosis by endogenous cytokines during infection. Apoptosis was observed in the spleen but not in the liver of infected mice, whereas the induction of liver necrosis was evident by rising levels of serum aminotransferases in these animals. Apoptosis was detected in the liver of L. monocytogenes-infected mice which had been treated with monoclonal antibody (mAb) against tumor necrosis factor-alpha (TNF-alpha) or interleukin-6 (IL-6), or in TNF-alpha(-/-) mice, but not in gamma- interferon (IFN-gamma)(-/-) mice or mice which had been treated with mAb against IL-4 or IL-10. Augmentation of liver apoptosis in mice treated with mAb against TNF-alpha or IL-6 or in TNF-alpha(-/-) mice correlated with the increase in bacterial numbers in the organ, while no augmentation of apoptosis was observed in the liver of IFN-gamma(-/-) mice irrespective of the marked increase in bacterial numbers in the organs, indicating that augmentation of liver apoptosis may not be merely due to the increase in bacterial growth in the organs. These results suggest that TNF-alpha and IL-6 may play an important role in protecting the liver from apoptosis in lethal L. monocytogenes infection.

The mucosal phase of Listeria infection

Listeria monocytogenes is an enteroinvasive bacterial pathogen of man and animals. Listeriae have been shown capable of infecting the host by translocating from the intestinal lumen through Peyer's Patches (PP), however, results of experiments now indicate that these facultative intracellular parasites may also translocate through PP-independent routes. With regards to this, on occasion we observed that listeriae were absent from the PP of mice inoculated intragastrically with L. monocytogenes, but were present in the mesenteric lymph nodes of these same mice. These observations suggested that PP were not necessary for listerial translocation from the intestinal lumen. Two experimental approaches were used to determine whether luminal listeriae could indeed infect the host through PP-independent routes. First, since it is known that: 1) following the intragastric inoculation of L. monocytogenes, listeriae rapidly transit the length of the gastrointestinal tract and reside in the colonic lumen for up to a week, 2) the colon lacks PP, and 3) the descending colon and rectum are drained exclusively by the caudal lymph node (CLN), it was determined whether colonic listeriae could access the CLN. Inoculation of listeriae into the rectum of mice resulted in the infection of the CLN which indicated that PP were not required for listerial translocation. Second, since germfree SCID mice lack PP, it was determined whether listeriae could translocate from the intestinal lumen and infect these immunoincompetent mice. Shortly after the intragastric inoculation of L. monocytogenes into germfree SCID mice, listeriae were found in the mesenteries, livers and spleens. These results also indicate that PP are not required for listerial translocation from the intestinal lumen. One possible route of translocation from the intestinal lumen might occur by listeriae entering enterocytes. Results were obtained showing that listeriae were capable of entering cultured mouse small intestine enterocytes. Internalized listeriae were observed to multiply and spread intracellularly between enterocytes.