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Background: The authors recently found that a CD31 agonist peptide reaches macrophages in injured aortas and exerts beneficial effects on apolipoprotein E-knockout (Apo E−/−) mice subjected to angiotensin (Ang) II infusion, a model of experimental acute aortic dissection and intramural hematoma (ADIM). Objectives: The purpose of this study was to evaluate the therapeutic potential of a drug-suitable agonist peptide in experimental ADIM. Methods: P8RI, a retro-inverso sequence of the best candidate identified by functional in vitro screening of a peptide library, passed an absorption, distribution, metabolism, excretion and toxicology analysis. Apo E−/− mice (male, 28-week-old) implanted with Ang II-releasing pumps received P8RI (2.5 mg/kg/day) or vehicle from day 14 (n = 10/group). Leukocytes were analyzed by flow cytometry. Healing features of human and mouse dissected aortic segments were assessed by histology and immunofluorescence. The effect of CD31 on macrophages was evaluated using cells from CD31−/− mice and P8RI, in vitro. Results: Human and experimental ADIM were characterized by the infiltration of proinflammatory macrophages. The absence of CD31 enhanced the proinflammatory polarization of macrophages, whereas the CD31 agonist P8RI favored reparative macrophages both in vitro and in vivo. The administration of P8RI after the occurrence of ADIM prevented aneurysmal transformation by promoting the resolution of intramural hematoma and the production of collagen in dissected aortas in vivo, associated with enrichment of M2 macrophages at the site of injury. Conclusions: CD31 signaling promotes the switching of proinflammatory macrophages to the reparative phenotype and favors the healing of experimental dissected aortas. Treatment with a drug-suitable CD31 agonist may facilitate the clinical management of ADIM.

Background: CD31 is a key transmembrane neutrophil immunoregulatory receptor. Mesenteric ischemia/reperfusion-induced neutrophil activation leads to a massive cleavage and shedding of the most extracellular domains of CD31 into plasma, enhancing the deleterious effect of neutrophil activation. We have evaluated the preventive therapeutic potential of an engineered synthetic octapeptide (P8RI), which restores the inhibitory intracellular signaling of cleaved CD31, in an experimental model of acute mesenteric ischemia/reperfusion. Methods: In a randomized, controlled, and experimenter-blinded preclinical study, mesenteric ischemia/reperfusion (I/R) was induced in Wistar rats by superior mesenteric artery occlusion for 30 min followed by 4 h of reperfusion. Three groups of rats were compared: I/R + saline perfusion (I/R controls group, n = 7), I/R + preventive P8RI perfusion (P8RI group, n = 7), and sham-operated rats + saline perfusion (sham group, n = 7). Results: Compared with I/R controls, P8RI perfusion significantly decreased intestinal ischemia/reperfusion injury (Chiu’s score, P = 0.01; epithelial area, P = 0.001) and bacterial translocation (plasma Escherichia coli DNA, P = 0.04) and could limit intestinal bleeding (P = 0.09). P8RI decreased neutrophil activation assessed by matrix metalloproteinase-9 release in plasma (P < 0.001) and in the intestinal wall, albeit without statistical significance (P = 0.06 and P = 0.058 for myeloperoxydase). Inhibition of CD31 cleavage from neutrophils could play a major role in the protective effects of P8RI (P < 0.0001). Conclusions: Preventive administration of P8RI, a CD31-agonist peptide, could decrease I/R-induced intestinal injury by potentially limiting neutrophil activation.

CD31, a trans-homophilic inhibitory receptor expressed on both T- and B-lymphocytes, drives the mutual detachment of interacting leukocytes. Intriguingly, T cell CD31 molecules relocate to the immunological synapse (IS), where the T and B cells establish a stable interaction.Here, we show that intact CD31 molecules, which are able to drive an inhibitory signal, are concentrated at the periphery of the IS but are excluded from the center of the IS. At this site, were the cells establish the closest contact, the CD31 molecules are cleaved, and most of the extracellular portion of the protein, including the trans-homophilic binding sites, is shed from the cell surface.T cells lacking CD31 trans-homophilic binding sites easily establish stable interactions with B cells; at the opposite, CD31 signaling agonists inhibit T/B IS formation as well as the ensuing helper T cell activation and function. Confocal microscopy and flow cytometry analysis of experimental T/B IS shows that the T cell inhibitory effects of CD31 agonists depend on SHP-2 signaling, which reduces the phosphorylation of ZAP70.The analysis of synovial tissue biopsies from patients affected by rheumatoid arthritis showed that T cell CD31 molecules are excluded from the center of the T/B cell synapses invivo. Interestingly, the administration of CD31 agonists invivo significantly attenuated the development of the clinical signs of collagen-induced arthritis in DBA1/J mice.Altogether, our data indicate that the T cell co-inhibitory receptor CD31 prevents the formation of functional T/B immunological synapses and that therapeutic strategies aimed at sustaining CD31 signaling will attenuate the development of autoimmune responses invivo.

BACKGROUND - : The atheromodulating activity of B cells during the development of atherosclerosis is well documented, but the mechanisms by which these cells are regulated have not been investigated. METHODS AND RESULTS - : Here, we analyzed the contribution of Qa-1-restricted CD8 regulatory T cells to the control of the T follicular helper-germinal center B-cell axis during atherogenesis. Genetic disruption of CD8 regulatory T cell function in atherosclerosis-prone apolipoprotein E knockout mice resulted in overactivation of this axis in secondary lymphoid organs, led to the increased development of tertiary lymphoid organs in the aorta, and enhanced disease development. In contrast, restoring control of the T follicular helper-germinal center B-cell axis by blocking the ICOS-ICOSL pathway reduced the development of atherosclerosis and the formation of tertiary lymphoid organs. Moreover, analyses of human atherosclerotic aneurysmal arteries by flow cytometry, gene expression analysis, and immunofluorescence confirmed the presence of T follicular helper cells within tertiary lymphoid organs. CONCLUSIONS - : This study is the first to demonstrate that the T follicular helper-germinal center B-cell axis is proatherogenic and that CD8 regulatory T cells control the germinal center reaction in both secondary and tertiary lymphoid organs. Therefore, disrupting this axis represents an innovative therapeutic approach.