We recently described an inducible human TNF transgenic mouse line (ihTNFtg) that develops psoriasis-like arthritis after doxycycline stimulation and analysed the pathogenesis of arthritis in detail. Here, we show that the skin phenotype of these mice is characterized by hyperproliferation and aberrant activation of keratinocytes, induction of pro-inflammatory cytokines, and infiltration with Th1 and Treg lymphocytes, particularly with macrophage infiltration into lesional skin, thus pointing to a psoriasis-like phenotype. To reveal the contribution of T cells and macrophages to the development of TNF-mediated psoriasis, ihTNFtg mice were crossbred into RAG1 mice lacking mature T and B cells. Surprisingly, the psoriatic phenotype in the double mutants was not reduced; rather, it was enhanced. The skin showed significantly increased inflammation and in particular, increased infiltration by macrophages. Consequently, depletion of macrophages in RAG1 or wild-type mice led to decreased disease severity. On the contrary, depletion of Treg cells in wild-type mice increased both psoriasis and the number of infiltrating macrophages, while adoptive transfer of Foxp3-positive cells into RAG1 or wild-type mice decreased both the development of psoriasis and macrophage infiltration. Thus, we conclude that Treg lymphocytes inhibit the pro-inflammatory activity of macrophages, which are the major immune effector cells in hTNF-mediated psoriasis. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Four-and-a-half LIM domain protein 2 (FHL2) is a multifunctional adaptor protein with fine-tuning adjustment properties. It acts as a regulator of signaling cascades but also as a cofactor of transcription and controls several anti-inflammatory immune responses. Recently, we described FHL2 as a novel regulator of influenza A virus propagation. We have shown that in vitro FHL2 restricts viral replication by accelerating the interferon regulatory factor 3-dependent transcription of the Ifnb1 gene. In this work, we unraveled an ambiguous role of FHL2 during influenza A virus infection in vivo. Although FHL2 restrained viral replication during the first 24 hours of infection, it significantly delayed viral clearance afterward. Comparison of lung immune status of wild-type and FHL2 knockout mice during influenza virus infection did not acknowledge significant differences in the innate host immune response but revealed an improved migration of dendritic cells from infected lungs into draining lymph nodes as well as increased levels of activated CD8 T lymphocytes accumulated in the lungs of FHL2 knockout mice.

Four and a half LIM domain protein 2 (Fhl2) is an intracellular adaptor molecule with a high protein-protein interaction capacity. It acts as a modulator of several signaling molecules in the cytosol and as a cofactor of transcription in the nucleus. Recent studies suggest the role of Fhl2 in tissue repair and the anti-inflammatory response. Herein, we show that Fhl2-deficient mice develop a more severe psoriatic arthritis disease under induction of the inducible human tumor necrosis factor (hTNF) transgene than wild-type mice. The disease was accompanied by increased infiltration of activated macrophages and T regulatory cells in skin and digit joints as well as by increased expression of matrix metalloproteases and bone-specific proteases. The more severe pathogenesis of psoriatic arthritis in Fhl2 knockout mice coincided with enhanced levels of soluble hTNF cytokine, but surprisingly not with transcription of the hTNF transgene. Studying the shedding of cell membrane-bound hTNF by Adam17, a known Fhl2 interacting protein, revealed an enhanced release of TNF in the absence of Fhl2. In summary, our results show that Fhl2 anticipates the emerging inflammation and specifically the development of psoriatic arthritis by impeding the Adam17-mediated release of TNF.

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Recently, we showed that infection of primary lung tumorbearing mice with oncolytic influenza A viruses (IAVs) led to strong virus-induced tumor cell lysis but also to restoration of immune competence of innate immune cells. Murine B16-F10 melanoma cells are known for their high lung tropism and progressive growth. As these cells are also highly permissive for IAVs, we analyzed their oncolytic and immunomodulatory efficiency against pulmonary B16-F10 lung metastases in vivo. IAV infection abrogated the melanoma-mediated immune suppression in the lung and induced a more than 50% cancer cell lysis. The oncolytic effect reached maximal efficacy 3 days post-infection, but it was not sustained over time. In order to maintain the virus-induced anti-tumor effect, mice with melanoma-derived lung cancers were treated in addition to influenza virus infection with an immune checkpoint inhibitor against programmed death-1 receptor (PD-1). The combined IAV and immune checkpoint inhibition (ICI) therapy resulted in a sustained anti-tumor efficacy, keeping the lung melanoma mass at day 12 of IAV infection still reduced by 50% over the control mice. In conclusion, ICI treatment strongly enhanced the oncolytic effect of influenza virus infection, suggesting that combined treatment is a promising approach against metastatic pulmonary melanoma.

Contact hypersensitivity (CHS) is an established animal model for allergic contact dermatitis. Dendritic cells (DCs) play an important role in the sensitization phase of CHS by initiating T cell responses to topically applied haptens. The cannabinoid receptors 1 (CB1) and 2 (CB2) modulate DC functions and inflammatory skin responses, but their influence on the capacity of haptenized DCs to induce CHS is still unknown. We found lower CHS responses to 2,4-dinitro-1-fluorobenzene (DNFB) in wild type (WT) mice after adoptive transfer of haptenized Cnr2−/− and Cnr1−/−/Cnr2−/− bone marrow (BM) DCs as compared to transfer of WT DCs. In contrast, induction of CHS was not affected in WT recipients after transfer of Cnr1−/− DCs. In vitro stimulated Cnr2−/− DCs showed lower CCR7 and CXCR4 expression when compared to WT cells, while in vitro migration towards the chemokine ligands was not affected by CB2. Upregulation of MHC class II and co-stimulatory molecules was also reduced in Cnr2−/− DCs. This study demonstrates that CB2 modulates the maturation phenotype of DCs but not their chemotactic capacities in vitro. These findings and the fact that CHS responses mediated by Cnr2−/− DCs are reduced suggest that CB2 is a promising target for the treatment of inflammatory skin conditions.

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Recently, we established a doxycycline-inducible human tumor necrosis factor alpha (TNFα)-transgenic mouse line, ihTNFtg. Non-induced young and elderly mice showed low but constitutive expression of hTNFα due to promoter leakiness. The persistently present hTNFα stimulated endogenous pro-inflammatory mouse mS100A8/A9 alarmins. Secreted mS100A8/A9 in turn induced the expression and release of mouse mTNFα. The continuous upregulation of pro-inflammatory mTNFα and mS100A8/A9 proteins, due to their mutual expression dependency, gradually led to increased levels in colon tissue and blood. This finally exceeded the threshold levels tolerated by the healthy organism, leading to the onset of intestinal inflammation. Here, recombinant hTNFα functioned as an initial trigger for the development of chronic inflammation. Crossing ihTNFtg mice with S100A9 KO mice lacking active S100A8/A9 alarmins or with Rag1 KO mice lacking T and B lymphocytes completely abrogated the development of colonic inflammation, despite the still leaky hTNFα promoter. Furthermore, both the intensity of the immune response and the strength of immunosuppressive Treg induction was found to depend on the major histocompatibility complex (MHC) genetic composition. In summary, the onset of intestinal inflammation in elderly mice depends on at least four factors that have to be present simultaneously: TNFα upregulation, S100A8/A9 protein expression, functional T lymphocytes and genetic composition, with the MHC haplotype being of central importance. Only joint action of these factors leads to chronic intestinal inflammation, while absence of any of these determinants abrogates the development of the autoimmune disorder.