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Inflammatory cell recruitment after myocardial infarction needs to be tightly controlled to permit infarct healing while avoiding fatal complications such as cardiac rupture. Growth differentiation factor-15 (GDF-15), a transforming growth factor-β (TGF-β)-related cytokine, is induced in the infarcted heart of mice and humans. We show that coronary artery ligation in Gdf15-deficient mice led to enhanced recruitment of polymorphonuclear leukocytes (PMNs) into the infarcted myocardium and an increased incidence of cardiac rupture. Conversely, infusion of recombinant GDF-15 repressed PMN recruitment after myocardial infarction. In vitro, GDF-15 inhibited PMN adhesion, arrest under flow and transendothelial migration. Mechanistically, GDF-15 counteracted chemokine-triggered conformational activation and clustering of [β.sub.2] integrins on PMNs by activating the small GTPase Cdc42 and inhibiting activation of the small GTPase Rap1. Intravital microscopy in vivo in 6df15-deficient mice showed that Gdf-15 is required to prevent excessive chemokine-activated leukocyte arrest on the endothelium. Genetic ablation of [β.sub.2] integrins in myeloid cells rescued the mortality of 6df15-deficient mice after myocardial infarction. To our knowledge, GDF-15 is the first cytokine identified as an inhibitor of PMN recruitment by direct interference with chemokine signaling and integrin activation. Loss of this anti-inflammatory mechanism leads to fatal cardiac rupture after myocardial infarction., The wound healing response after myocardial infarction involves a cascade of molecular and cellular events that leads to a replacement of the necrotic area with granulation tissue and, eventually, a [...]

Nonalcoholic steatohepatitis (NASH) is induced by steatosis and metabolic inflammation. While involvement of the innate immune response has been shown, the role of the adaptive immune response in NASH remains controversial. Likewise, the role of regulatory T cells (Treg) in NASH remains unclear although initial clinical trials aim to target these regulatory responses. High‐fat high‐carbohydrate (HF‐HC) diet feeding of NASH‐resistant BALB/c mice as well as the corresponding recombination activating 1 (Rag)‐deficient strain was used to induce NASH and to study the role of the adaptive immune response. HF‐HC diet feeding induced strong activation of intrahepatic T cells in BALB/c mice, suggesting an antigen‐driven effect. In contrast, the effects of the absence of the adaptive immune response was notable. NASH in BALB/c Rag1−/− mice was substantially worsened and accompanied by a sharp increase of M1‐like macrophage numbers. Furthermore, we found an increase in intrahepatic Treg numbers in NASH, but either adoptive Treg transfer or anti‐cluster of differentiation (CD)3 therapy unexpectedly increased steatosis and the alanine aminotransferase level without otherwise affecting NASH. Conclusion: Although intrahepatic T cells were activated and marginally clonally expanded in NASH, these effects were counterbalanced by increased Treg numbers. The ablation of adaptive immunity in murine NASH led to marked aggravation of NASH, suggesting that Tregs are not regulators of metabolic inflammation but rather enhance it. [ABSTRACT FROM AUTHOR]

For the development of autoimmune hepatitis (AIH), genetic predisposition and environmental triggers are of major importance. Although experimental AIH can be induced in genetically susceptible mice, the low precursor frequency of autoreactive T cells hampers a deeper analysis of liver-specific T cells. Here, we established a system where the model antigen hemagglutinin (HA) is expressed exclusively in hepatocytes of Rosa26-HA mice following administration of a replication deficient adenovirus expressing Cre recombinase (Ad-Cre). Under these conditions, hepatocytes mimic the generation of altered-self neoantigens. To follow autoreactive T cells during AIH, we adoptively transferred HA-­specific Cl4-TCR and 6.5-TCR T cells into Ad-Cre infected ­Rosa26-HA mice. Alternatively, Rosa26-HA mice have been crossed with TCR transgenic mice that were infected with Ad-Cre to break hepatic tolerance and induce the expression of the HA antigen as a hepatic self-antigen. Surprisingly, neither adoptive transfer nor a very high precursor frequency of autoreactive T cells was able to break tolerance in the context of adenoviral infection. The low proliferation of the antigen experienced autoreactive T cells despite the presence of the autoantigen and inflammation points to anergy as a potential tolerance mechanism. This model underscores the crucial importance of genetic susceptibility to break tolerance against hepatic autoantigens. [ABSTRACT FROM AUTHOR]