P012 Control of mycobacterial infection in “humanized” TNF knock-in mice

Introduction TNF is associated with the development of human immunopathologies and involved in host defense. TNF blockade to treat autoimmune inflammatory diseases revealed a crucial and non-redundant role of TNF for the control to tuberculosis infection. Tuberculosis is a chronic infection and sustained TNF and Th1 immune responses are crucial to control infection. To test and select specific human TNF inhibitors requires a special animal model. Therefore a mouse was developed where murine TNF was replaced by human TNF (human TNF knock-in) and we investigated host resistance to mycobacterial infection. Methods Human TNF KI mice (humanized TNF mice) have been developed (Kruglov et al., in preparation) and studied for their capacity to generate protective cell-mediated immune responses and resistance to Mycobacterium bovis BCG and M. tuberculosis infections. Bone marrow derived macrophages (BMDM) infected with BCG have been analyzed for the ability to respond to in vitro infection. Results BMDM from humanized TNF KI mice were able to produce cytokines and nitrites in response to BCG infection as wild-type macrophages. BCG-induced NF-kB activation was similar in humanized TNF KI and wild-type macrophages whereas TNF KO cells presented impaired NF-kB phosphorylation. Humanized TNF KI mice survived to acute and chronic M. bovis BCG and M. tuberculosis infections as wild-type mice while TNF KO mice rapidly succumbed. Bacterial burden was controlled in humanized TNF KI, while overwhelming infection was evident in TNF KO mice. Bactericidal mechanism such as macrophage iNOS activation was analyzed in the liver of infected mice. iNOS protein levels were decreased in humanized TNF mice compared to wild-type mice at early infection, but these levels became comparable at late infection. The pattern of serum and lung cytokines showed that humanized TNF KI mice were able to activate Th1 type immune responses producing amounts of IFN γ and IL-12 similar to that observed in wild-type mice after an infection. Conclusion This study in humanized TNF mice demonstrates that human TNF can replace the function of mouse TNF during an intracellular bacterial infection providing resistance, NF-kB activation and Th1 immune responses. Therefore, human TNF KI mice may be highly relevant to test novel biologics neutralizing human TNF and their effects on inflammatory and infectious pathologies.