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 D 2 , in the development of acute inflammation. D 2 is mostly expressed on macrophages and contributes to the development of chronic inflammation. In contrast, we found that D -knockout dramatically increases mortality in the cecal ligation and puncture sepsis model and LPS-induced endotoxemia.This pathologic outcome of D -deficient mice is associated with a reduced number of monocytederived macrophages and an increased number of neutrophils in their lungs. However, the tracking of adoptively transferred fluorescently labeled wild-type (WT) and D −/− 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 Ddeficient mice followed by LPS challenge, showed only slightly reduced mortality. Surprisingly, the injection of WT neutrophils to the bloodstream of D −/− mice markedly increased migration of monocyte-derived macrophage to lungs and dramatically improves survival. D -deficient neutrophils demonstrate increased necrosis/pyroptosis. D 2 -mediated macrophage accumulation in the lungs promotes efferocytosis that reduced mortality. Hence, integrin D 2 implements a complex defense mechanism during endotoxemia, which is mediated by macrophages via a neutrophildependent pathway.

Oxidation of polyunsaturated fatty acids contributes to different aspects of the inflammatory response due to the variety of products generated. Specifically, the oxidation of DHA produces the end-product, carboxyethylpyrrole (CEP), which forms a covalent adduct with proteins via an ϵ-amino group of lysines. Previously, we found that CEP formation is dramatically increased in inflamed tissue and CEP-modified albumin and fibrinogen became ligands for αDβ2 (CD11d/CD18) and αMβ2 (CD11b/CD18) integrins. In this study, we evaluated the effect of extracellular matrix (ECM) modification with CEP on the adhesive properties of M1-polarized macrophages, particularly during chronic inflammation. Using digested atherosclerotic lesions and in vitro oxidation assays, we demonstrated the ability of ECM proteins to form adducts with CEP, particularly, DHA oxidation leads to the formation of CEP adducts with collagen IV and laminin, but not with collagen I. Using integrin αDβ2-transfected HEK293 cells, WT and αD−/− mouse M1-polarized macrophages, we revealed that CEP-modified proteins support stronger cell adhesion and spreading when compared with natural ECM ligands such as collagen IV, laminin, and fibrinogen. Integrin αDβ2 is critical for M1 macrophage adhesion to CEP. Based on biolayer interferometry results, the isolated αD I-domain demonstrates markedly higher binding affinity to CEP compared to the “natural” αDβ2 ligand fibrinogen. Finally, the presence of CEP-modified proteins in a 3D fibrin matrix significantly increased M1 macrophage retention. Therefore, CEP modification converts ECM proteins to αDβ2-recognition ligands by changing a positively charged lysine to negatively charged CEP, which increases M1 macrophage adhesion to ECM and promotes macrophage retention during detrimental inflammation, autoimmunity, and chronic inflammation.

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