Short communicationThe absence of TNF permits myeloid Arginase 1 expression in experimental L. monocytogenes infection
Introduction
Failure to resolve inflammation is intrinsic in many human pathologies. Mechanisms that influence and modulate the inflammatory response are therefore, of general interest for our understanding of the underlying disease processes. One of the classical protagonists of inflammation is the proinflammatory cytokine tumor necrosis factor (TNF). This cytokine is present in high concentrations in inflammatory sites and has a variety of functions, such as activating cells and inducing the expression of functional cell surface molecules (Sedgwick et al., 2000). TNF is expressed by macrophages and T cells early after an immunological challenge and has been identified as a target for therapeutic intervention in a variety of chronic and autoimmune inflammatory diseases, including rheumatoid arthritis (RA) and inflammatory bowel disease (IBD) (Efimov et al., 2009, Udalova et al., 2016a). Anti TNF-therapy that blocks TNF activity using antagonists based on antibodies or TNFR fusion proteins is now a proven method of treatment for these pathologies (Udalova et al., 2016b). However, TNF has also been identified to be essential in the establishment of protective immunity to infection. Experiments that block TNF and the use of gene-deficient animals have resulted in a list of bacterial and parasitic pathogens that are controlled by a functioning TNFR1-TNF signaling axis (Pfeffer et al., 1993, Rothe et al., 1993, Wilhelm et al., 2001). The implicit mechanisms that contribute to the protective role of TNF have been difficult to define due to the ubiquitous expression of this pleiotropic cytokine. In the murine model of experimental cutaneous leishmaniasis, TNF-deficiency induced a progressive visceral infection and was ultimately fatal in the normally resistant mouse strain C57BL/6 (Wilhelm et al., 2001). The underlying cause of this lack of protection proved to be elusive since both innate and adaptive immune responses seem largely unchanged. However, it has recently been shown that TNF is essential for the suppression of Arginase 1 (Arg1) and other genes of the pro-homeostatic alternatively activated macrophage signature due to a restriction of accessibility of their promoters and enhancers (Schleicher et al., 2016). Thus, TNF was deemed irreplaceable for an effective differentiation of monocytes to classically activated macrophages (Schleicher et al., 2016). Indeed, a large percentage of skin and lymph node-resident macrophages and inflammatory dendritic cells (DC) from Leishmania (L.) major infected B6.TNF−/− mice co-expressed classically and alternatively activated macrophage signature molecules such as Arg1 and iNOS, respectively (Schleicher et al., 2016). This co-expression resulted in a lack of the central effector molecule nitric oxide (NO) in the lesion and the draining lymph node in infected tissues presumably due to a depletion of L-arginine, the substrate of both enzymes. This biological function of TNF to restrict alternative macrophage differentiation during the inflammatory response to L. major has also been demonstrated in tumor models and we hypothesized that it would be applicable generally. Therefore, we used Listeria (L.) monocytogenes infection as a bacterial model with a well-established history of myeloid differentiation to analyze the consequences of TNF-deficiency in more detail (Serbina et al., 2003). The TNF-deficient mouse strain (B6.TNF−/−) was highly susceptible to the pathogen. Inflammatory splenic macrophages from B6. TNF−/− mice could be identified using Ly6 C and CD11b. These cells exhibited a high bacterial burden, normal iNOS and an elevated Arg1 and TGM2 expression.
Section snippets
Animals and infection
Eight to 16-week-old C57BL/6 (B6. WT) and B6.TNF−/− mice were used in all experiments. All mice were housed and bred in a certified SPF environment. To infect the mice we cultured a single colony of L. monocytogenes (obtained from Prof. Dirk Busch, Institute for Microbiology, Technical University Munich, Germany) in brain-heart infusion broth (BD Biosciences, North Ryde, Australia) overnight at 37 °C with shaking. The overnight culture was added to fresh medium at volume ratio 1: 50 and cultured
Results
The experimental infection of mice with L. monocytogenes is a well-validated model for a bacterial infection that relies on macrophages as predominant host cells. Spleen and liver are the two major target organs of systemic L. monocytogenes infection. In B6.WT mice the infection reached a peak of 104 bacteria per organ at day 3 post-infection (p.i.) and started to subside thereafter (Fig. 1A and B). At the same time post infection, in spleens and livers of immunocompromised B6.TNF−/− mice the
Discussion
A deficiency in the TNF-TNFR1 signaling pathway causes a significant aggravation of the pathology of C57BL/6 mice infected with L. monocytogenes (Grivennikov et al., 2005, Pfeffer et al., 1993, Rothe et al., 1993). Investigations using a tissue-specific TNF-deficiency have been able to localize the source of the protective production of TNF in macrophages (Grivennikov et al., 2005). The TNF-deficient strain B6.TNF−/− displayed a rapid increase of the bacterial burden in spleen and liver within 4
Conflict of interest
The authors state that they had no conflict of interest.
Acknowledgments
We wish to thank Amanda Patchett for qPCR advice, and Jocelyn Darby and Terry Pinfold for technical help. We would also like to thank the staff of the animal facility of the University of Tasmania. The work was supported by the Menzies Institute of Medical Research Tasmania and an IPGR scholarship to X. Li.
References (15)
- et al.
Tumor necrosisfactor and the consequences of its ablation in vivo
Mol.Immunol.
(2009) - et al.
Distinct and nonredundant in vivo functions of TNF produced by T cells and macrophages/neutrophils: protective and deleterious effects
Immunity
(2005) - et al.
TNF counterbalances the emergence of M2 tumor macrophages
Cell.Rep.
(2015) - et al.
Macrophage activation and polarization: nomenclature and experimental guidelines
Immunity
(2014) - et al.
Mice deficient for the 55 kd tumor necrosis factor receptor are resistant to endotoxic shock, yet succumb to L. monocytogenes infection
Cell
(1993) - et al.
TNF-mediated restriction of Arginase 1 expression in myeloid cells triggers type 2 NO synthase activity at the site of infection
Cell. Rep.
(2016) - et al.
Tumor necrosis factor: a master-regulator of leukocyte movement
Immunol. Today
(2000)
Cited by (9)
Immune regulation by monocytes
2018, Seminars in ImmunologyCitation Excerpt :Until recently, the association between TNF and M2 macrophages was unclear. However, we now know from several diverse inflammatory and infection models that TNF is an essential negative regulator of M2 gene expression [22,38,46,47]. Indeed, complete absence of TNF or the type I TNF receptor causes increased M2 gene expression mediated in part to increased sensitivity to IL-4 and IL-13 [46].
Gene-selective transcription promotes the inhibition of tissue reparative macrophages by TNF
2022, Life Science AllianceAbsence of TNF Leads to Alternative Activation in Peritoneal Macrophages in Experimental Listeria Monocytogenes Infection
2022, Immunological InvestigationsSusceptibility to Intracellular Infections: Contributions of TNF to Immune Defense
2020, Frontiers in MicrobiologyInnate and adaptive immune responses during Listeria monocytogenes infection
2019, Microbiology SpectrumInnate and adaptive immune responses during listeria monocytogenes infection
2019, Gram-Positive Pathogens