Neutrophil-macrophage interplay is a fine-tuning mechanism that regulates the innate immune response during infection and inflammation. Cell surface receptors play an essential role in neutrophil and macrophage functions. The same receptor can provide different outcomes within diverse leukocyte subsets in different inflammatory conditions. Understanding the variety of responses mediated by one receptor is critical for the development of anti-inflammatory treatments. In this study, we evaluated the role of a leukocyte adhesive receptor, integrin αD β2 , in the development of acute inflammation. αD β2 is mostly expressed on macrophages and contributes to the development of chronic inflammation. In contrast, we found that αD -knockout dramatically increases mortality in the cecal ligation and puncture sepsis model and LPS-induced endotoxemia. This pathologic outcome of αD -deficient mice is associated with a reduced number of monocyte-derived macrophages and an increased number of neutrophils in their lungs. However, the tracking of adoptively transferred fluorescently labeled wild-type (WT) and αD-/- monocytes in WT mice during endotoxemia demonstrated only a moderate difference between the recruitment of these two subsets. Moreover, the rescue experiment, using i.v. injection of WT monocytes to αD -deficient mice followed by LPS challenge, showed only slightly reduced mortality. Surprisingly, the injection of WT neutrophils to the bloodstream of αD-/- mice markedly increased migration of monocyte-derived macrophage to lungs and dramatically improves survival. αD -deficient neutrophils demonstrate increased necrosis/pyroptosis. αD β2 -mediated macrophage accumulation in the lungs promotes efferocytosis that reduced mortality. Hence, integrin αD β2 implements a complex defense mechanism during endotoxemia, which is mediated by macrophages via a neutrophil-dependent pathway.

The accumulation of pro-inflammatory macrophages in the inflamed vascular wall is a critical step in atherogenesis. The mechanism of macrophage retention within the site of inflammation is not understood yet. High adhesion that prevents macrophage migration is one of the potential mechanisms. We previously showed that integrin α D β 2 is upregulated on pro-inflammatory macrophages, promotes macrophage retention, and contributes to atherogenesis. However, we have not identified a key ligand for α D β 2 within the tissue, since α D β 2 does not interact with major ECM proteins, collagens, and laminins. We recently found that during acute inflammation, the oxidation of docosahexaenoic acid (DHA) leads to the generation of end product carboxyethylpyrrole (CEP), which forms an adduct with fibrinogen and albumin via ε-amino group of lysines. Moreover, we revealed that macrophages adhered to CEP-modified albumin in α D β 2 -dependent manner. Now we are testing a hypothesis that DHA oxidation is a universal mechanism during chronic inflammatory diseases that promotes the generation of CEP adducts with different ECM proteins and forms α D β 2 -mediated strong anchorage of macrophages, which is critical for macrophage retention during chronic inflammation. We detected CEP-modified proteins in digested atherosclerotic lesions by western blot. In vitro DHA oxidation leads to the formation of CEP adducts with collagen IV and laminin but not with collagen I. Using α D β 2 -transfected HEK293 cells, WT and α D -/- mouse macrophages, we revealed that CEP-modified proteins support stronger cell adhesion and spreading to compare with natural macrophage ligands. Using site-directed mutagenesis, we generated mutant α D I-domains and α D β 2 -transfected cells with single amino acid substitutions. Applying protein-protein binding and adhesion assays we detected one amino acid within integrin α D , K 246 , which is critical for α D β 2 binding to CEP-modified proteins. In summary, we propose a new mechanism of macrophage retention, which is based on inflammatory modifications of ECM with DHA end-product, CEP. The identification of a binding site for CEP-modified proteins within α D β 2 will help to develop a blocking reagent for the treatment of the inflammatory component of atherosclerosis.

A critical step in the development of chronic inflammatory diseases is the accumulation of proinflammatory macrophages in the extracellular matrix (ECM) of peripheral tissues. The adhesion receptor integrin ?(D)?(2) promotes the development of atherosclerosis and diabetes by supporting macrophage retention in inflamed tissue. We recently found that the end product of docosahexaenoic acid (DHA) oxidation, 2-(?-carboxyethyl)pyrrole (CEP), serves as a ligand for ?(D)?(2). CEP adduct with ECM is generated during inflammation-mediated lipid peroxidation. The goal of this project was to identify a specific inhibitor for ?(D)?(2)?CEP interaction that can prevent macrophage accumulation. Using a specially designed peptide library, Biacore-detected protein?protein interaction, and adhesion of integrin-transfected HEK 293 cells, we identified a sequence (called P5 peptide) that significantly and specifically inhibited ?(D)?CEP binding. In the model of thioglycollate-induced peritoneal inflammation, the injection of cyclic P5 peptide reduced 3-fold the macrophage accumulation in WT mice but had no effect in ?(D)-deficient mice. The tracking of adoptively transferred, fluorescently labeled WT and ?(?/?)(D) monocytes in the model of peritoneal inflammation and in vitro two-dimensional and three-dimensional migration assays demonstrated that P5 peptide does not affect monocyte transendothelial migration or macrophage efflux from the peritoneal cavity but regulates macrophage migration through the ECM. Moreover, the injection of P5 peptide into WT mice on a high-fat diet prevents macrophage accumulation in adipose tissue in an ?(D)?(2)-dependent manner. Taken together, these results demonstrate the importance of ?(D)?(2)-mediated macrophage adhesion for the accumulation of infiltrating macrophages in the inflamed ECM and propose P5 peptide as a potential inhibitor of atherogenesis and diabetes.