Intracellular and surface distribution of CD9 in human eosinophils

Abstract

Expression of CD9 is a feature of both eosinophils and platelets. We have investigated the CD9 expression on resting and activated eosinophils with regard to possibly interacting platelets. Mixed leukocytes were obtained from the platelet‐containing (PC) and platelet‐depleted (PD) peripheral blood of healthy donors. A cell membrane permeabilization technique, the FOG method, enabled us to detect the eosinophils as a separate population and permitted flow cytometric analysis of both surface and intracellular antigens. Monoclonal antibodies against CD61 were used to identify platelets. The CD9/CD61 ratio indicated that CD9 on resting eosinophils originates mainly from eosinophils and not from adhered platelets. No difference in CD9 expression was obtained between resting eosinophils in PC and PD blood. However, the expression of CD9 was decreased (p<0.05) on eosinophils in PMA‐activated PD blood but increased (p=0.001) in PC blood, probably due to interacting platelets since CD61 increased simultaneously. In addition, we were able to detect an intracellularly stored pool of CD9 in eosinophils which decreased after activation with PMA. Together these results indicate a translocation of intracellularly stored CD9 to the cell membrane upon activation, probably followed by a subsequent shedding.

MHC Class II and CD9 in Human Eosinophils Localize to Detergent-Resistant Membrane Microdomains

“…We have demonstrated here that surface expression of CD9 is comparable between human eosinophils and monocyte-derived DCs, further supporting eosinophils as professional APCs. As seen in previous studies, CD9 is abundant on the cell surface of eosinophils to such an extent as to be considered a marker for eosinophils (13). Here, we extend these studies showing, for the first time, the ultrastructural immunolocalization of CD9 in human eosinophils.…”

“…The tetraspanin CD9 is abundantly expressed on the surface of eosinophils and intracellularly, yet the function of CD9 in eosinophils remains unclear (13). Matsumoto and colleagues demonstrated that cross-linking CD9 in isolated human eosinophils with a monoclonal antibody followed by a secondary antibody caused eosinophil "activation," as measured by homotypic aggregation by flow cytometry (14).…”

Mouse pregnancy-specific glycoproteins: tissue-specific expression and evidence of association with maternal vasculature

“…CD9 is generally found on the cell surface; however, occasionally, it is located intracellularly e.g. in eosinophils and platelets, where it is stored pending transfer to the cell surface upon activation (Fernvik et al 1995, Brisson et al 1997.…”

The effect of in vitro activation and platelet interaction on the CD9 distribution and adhesion properties of human eosinophils

“…It has also been demonstrated that platelet activation by anti-CD9 antibodies is mediated by the FcgII-receptor [10], which indicate that CD9 can co-operate with other receptors to induce intracellular signalling. In addition, CD9 antigens are known to shed from the cell surface of leukaemic lymphoblasts from patients with acute lymphoblastic leukaemia [11], and an existing intracellular pool of CD9 in eosinophils has been proposed [12]. Taken together, these observations indicate that CD9 plays a role in the initial phase of cell activation.…”