History Highly pathogenic avian influenza viruses of the H5N1 subtype continue to cross the species barrier to infect humans and cause severe disease. H5N1 virus whereas no such differences were observed with the less virulent A/PR/8/34 (H1N1) virus. H5N1 infected TM mice displayed diminished cytokine production in lung tissue and a quantifiable decline of macrophages and neutrophils in the lungs post-infection. Moreover morphometric analysis of airway sections revealed less extensive inflammation in H5N1-infected TM mice compared with infected wild type mice. Conclusions The combined signaling from the TNF or IL-1 receptors promotes maximal lung inflammation that may contribute to the severity of disease caused by H5N1 virus infection. The emergence of the highly pathogenic H5N1 avian influenza virus and its associated high lethality still remains a public health concern. Since the re-emergence of the H5N1 subtype in 2003 there have been over 495 human cases worldwide of which approximately 60% have been fatal [1]. H5N1 virus infected patients initially present with fever coughing dyspnea and in some cases radiological evidence of bronchopneumonia [2 3 In severe cases bilateral pneumonia and the development of acute respiratory distress syndrome (ARDS) is followed by progressive respiratory failure [4 5 ARDS is a clinical syndrome usually secondary to an intense host cytokine and inflammatory response that JTT-705 includes increased levels of tumor necrosis factor alpha (TNF-α) [5-9]. Thus it has been suggested that elevated levels of cytokines in H5N1 infected patients may contribute to the overall pathogenesis of these viral infections further complicating recovery [10-13]. The hypothesis that an aberrant cytokine and subsequent cellular immune responses to H5N1 virus detrimentally affect severity and patient outcome has been understudied. In comparison to seasonal influenza strains H5N1 viruses are potent inducers of TNF and IL-1 cytokines both and studies [3 10 In mice studies demonstrated that no individual pro-inflammatory cytokine was responsible for the pathogenesis associated with JTT-705 virus Rabbit Polyclonal to MNK1 (phospho-Thr255). or bacterial infection [16-19]. Thus the lack of these individual cytokine receptors ultimately did not lead to an improvement in host survival following infection with H5N1 virus. However because of the functional redundancy of some cytokine products the effect of deleting only one cytokine might be masked by compensatory host responses. To determine the combined contributions of TNF and JTT-705 IL-1 signaling to the inflammatory responses to H5N1 virus infection we utilized triple mutant (TM) mice deficient in TNF (R1 and R2 receptors) and IL-1 (type I receptor) and measured their host responses to a virulent H5N1 virus. We found that TM mice survived longer exhibited less morbidity and displayed a reduction in lung inflammation and cytokine response compared to wild-type (WT) mice. The specific immune cell subpopulations contributing to the differences in inflammation observed between infected TM and WT mice are also presented here. This study shows an important role of the combined effects of TNF and IL-1 in contributing to the pathogenic outcome of H5N1 virus infection. Methods Virus Influenza A virus A/Hong Kong/483/97 (HK/483) isolated from a fatal case [20-22] and A/PR/8/34 (PR8; H1N1) were grown and titered in embryonating hen’s eggs and 50% egg infectious dose (EID50) was calculated as described previously [23 24 All experiments were performed in biosafety level 3 laboratories with enhancements as outlined in the Biomedical Microbiological and Biomedical Laboratory [25]. Mice Mouse strains (6-8 weeks old) utilized in these studies included: TNF-R1 TNF-R2 and IL-1-RI triple-mutant (TM) C57BL/6J × 129S background [18 19 26 27 IL-1-RI single cytokine receptor knock-out mice (IL-1-R KO) C57BL/6J × 129Sv –< 0.05). Moreover TM-infected mice lost significantly less weight at earlier time points than WT-infected mice (Figure 1B) whereas mock-infected controls that received PBS in place of virus gained approximately 6% body weight over the observation period (not shown). In contrast differences in morbidity and mortality between TM and WT mouse strains JTT-705 were not observed among PR8-inoculated mice. These results suggest that the lack of both IL-1-R and TNF-R signaling affects the outcome of H5N1 virus disease in mice. Figure 1 Morbidity and mortality in triple-mutant (TM) mice TM mice exhibited similar lung virus titers but displayed increased systemic spread of virus to brain tissue In an effort to identify biological mechanisms contributing to the enhanced.