SelK-2

Background:  Activated platelets form heterogeneous aggregates of platelets and monocytes, which are involved in a variety of inflammatory disorders. Some anti‐human leukocyte antigen (HLA) Class I antibodies have been shown to activate platelets.Materials and Methods:  Human leukocyte antigen‐A2‐positive or HLA‐A2‐negative platelets were incubated with HLA‐A2‐negative peripheral blood mononuclear cells (PBMNCs) in the presence of anti‐HLA‐A2 serum at 37°C. The binding of platelets to monocytes was analysed by flow cytometry. The levels of IL‐1 β and IL‐8 in the culture supernatant were determined by ELISA.Results:  Anti‐HLA‐A2 serum increased the formation of aggregates between monocytes and HLA‐A2‐positive platelets, but not HLA‐A2‐negative platelets, in a dose‐dependent manner. Antiserum also increased the number of platelets bound to monocytes in a time‐dependent manner. The addition of anti‐P‐selectin glycoprotein ligand (PSGL‐1) mAb almost completely inhibited the formation of platelet–monocyte aggregates as well as the number of platelets bound to monocytes. When HLA‐A2‐positive or HLA‐A2‐negative platelets were incubated with HLA‐A2‐negative PBMNCs in the presence of anti‐HLA‐A2, the level of IL‐1β and IL‐8 in the supernatant of coculture was significantly higher in HLA‐A2‐positive platelets than in HLA‐A2‐negative platelets. The addition of anti‐PSGL‐1 mAb partially but significantly inhibited the production of both IL‐1β and IL‐8.Conclusions:  The activation of platelets with anti‐HLA Class I alloantibody caused the formation of platelet–monocyte aggregates, followed by the production of IL‐1β and IL‐8, in a cognate antigen–antibody manner. The adhesive interaction of P‐selectin and PSGL‐1 at least partially contributed to these phenomena.

The pathogenesis of Crohn's disease (CD) is not known. However, monocytes and macrophages are thought to play important roles in the development of mucosal inflammation. Therefore, in this study, we examined the role of monocyte-endothelial cell interactions in senescence-accelerated mouse P1 (SAMP1)/Yit mice, a murine model of spontaneous ileitis. Fluorescence-labeled CD14+ monocytic cells isolated from the spleen and mesenteric lymph nodes of AKR/J (control) mice were injected into the tail veins of recipient (AKR/J and SAMP1/Yit) mice, and migration in the postcapillary venules (PCV) of Peyer's patches, submucosal venules, and villus microvessels of the terminal ileum was monitored by using an intravital microscope. Rolling and adhesion of CD14+ monocytic cells in the PCV of Peyer's patches and microvessels of the terminal ileum were increased in SAMP1/Yit mice. An imunohistochemical study showed increased expression of P-selectin glycoprotein-1 (PSGL-1), P-selectin, and vascular cell adhesion molecule-1 in the terminal ileum of SAMP1/Yit mice. Antibodies against these three adhesion molecules significantly inhibited adhesion of CD14+ monocytic cells to the PCV of Peyer's patches and microvessels of the terminal ileum, treatment with an anti-PSGL-1 monoclonal antibody (mAb) showing the strongest suppressive effect. Anti-PSGL-1 mAb also attenuated T cell adhesion in microvessels of intestinal mucosa. In addition, periodical administration of an anti-PSGL-1 mAb for 7 weeks significantly ameliorated ileitis of SAMP1/Yit mice. The results suggest that PSGL-1-P-selectin interaction plays an important role in monocyte-endothelial cell interactions and the development of ileitis in a murine model of CD and that the blockade of this adhesion molecule may be a novel strategy for treating CD.