Influenza-induced Tpl2 expression within alveolar epithelial cells is dispensable for host viral control and anti-viral immunity.

Tumor progression locus 2 (Tpl2) is a serine/threonine kinase that regulates the expression of inflammatory mediators in response to Toll-like receptors (TLR) and cytokine receptors. Global ablation of Tpl2 leads to severe disease in response to influenza A virus (IAV) infection, characterized by respiratory distress, and studies in bone marrow chimeric mice implicated Tpl2 in non-hematopoietic cells. Lung epithelial cells are primary targets and replicative niches of influenza viruses; however, the specific regulation of antiviral responses by Tpl2 within lung epithelial cells has not been investigated. Herein, we show that Tpl2 is basally expressed in primary airway epithelial cells and that its expression increases in both type I and type II airway epithelial cells (AECI and AECII) in response to influenza infection. We used Nkx2.1-cre to drive Tpl2 deletion within pulmonary epithelial cells to delineate epithelial cell-specific functions of Tpl2 during influenza infection in mice. Although modest increases in morbidity and mortality were attributed to cre-dependent deletion in lung epithelial cells, no alterations in host cytokine production or lung pathology were observed. In vitro, Tpl2 inhibition within the type I airway epithelial cell line, LET1, as well as genetic ablation in primary airway epithelial cells did not alter cytokine production. Overall, these findings establish that Tpl2-dependent defects in cells other than AECs are primarily responsible for the morbidity and mortality seen in influenza-infected mice with global Tpl2 ablation.

Tamoxifen administration induces histopathologic changes within the lungs of Cre-recombinase-negative mice: A case report.

Tamoxifen is commonly used as a cancer treatment in humans and for inducing genetic alterations using Cre-lox mouse models in the research setting. However, the extent of tamoxifen off-target effects in animal research is underappreciated. Here, we report significant changes in cellular infiltration in Cre-recombinase-negative mice treated with tamoxifen intraperitoneally. These changes were noted in the lungs, which were characterized by the presence of alveolitis, vasculitis, and pleuritis. Despite significant immunological changes in response to tamoxifen treatment, clinical symptoms were not observed. This study provides a cautionary note that tamoxifen treatment alone leads to histologic alterations that may obscure research interpretations and further highlights the need for the development of alternative mouse models for inducible Cre-mediated deletion.

Tumor Progression Locus 2 (Tpl2) Activates the Mammalian Target of Rapamycin (mTOR) Pathway, Inhibits Forkhead Box P3 (FoxP3) Expression, and Limits Regulatory T Cell (Treg) Immunosuppressive Functions.

The serine/threonine kinase tumor progression locus 2 (Tpl2, also known as Map3k8/Cot) is a potent inflammatory mediator that drives the production of TNFα, IL-1ß, and IFNγ. We previously demonstrated that Tpl2 regulates T cell receptor (TCR) signaling and modulates T helper cell differentiation. However, very little is known about how Tpl2 modulates the development of regulatory T cells (Tregs). Tregs are a specialized subset of T cells that express FoxP3 and possess immunosuppressive properties to limit excess inflammation. Because of the documented role of Tpl2 in promoting inflammation, we hypothesized that Tpl2 antagonizes Treg development and immunosuppressive function. Here we demonstrate that Tpl2 constrains the development of inducible Tregs. Tpl2(-/-) naïve CD4(+) T cells preferentially develop into FoxP3(+) inducible Tregs in vitro as well as in vivo in a murine model of ovalbumin (OVA)-induced systemic tolerance. Treg biasing of Tpl2(-/-) T cells depended on TCR signal strength and corresponded with reduced activation of the mammalian target of rapamycin (mTOR) pathway. Importantly, Tpl2(-/-) Tregs have basally increased expression of FoxP3 and immunosuppressive molecules, IL-10 and cytotoxic T lymphocyte-associated protein 4 (CTLA-4). Furthermore, they were more immunosuppressive in vivo in a T cell transfer model of colitis, as evidenced by reduced effector T cell accumulation, systemic production of inflammatory cytokines, and colonic inflammation. These results demonstrate that Tpl2 promotes inflammation in part by constraining FoxP3 expression and Treg immunosuppressive functions. Overall, these findings suggest that Tpl2 inhibition could be used to preferentially drive Treg induction and thereby limit inflammation in a variety of autoimmune diseases.