Key Points• Endothelial endoglin has a regulatory role in leukocyte trafficking through vascular endothelia.• Leukocytes and endothelial cells interact via integrin receptors and endoglin, being this cell adhesion process stimulated by inflammatory stimuli.Human endoglin is an RGD-containing transmembrane glycoprotein identified in vascular endothelial cells. Although endoglin is essential for angiogenesis and its expression is up-regulated in inflammation and at sites of leukocyte extravasation, its role in leukocyte trafficking is unknown. This function was tested in endoglin heterozygous mice (Eng ؉/؊ ) and their wild-type siblings Eng ؉/؉ treated with carrageenan or LPS as inflammatory agents. Both stimuli showed that inflammation-induced leukocyte transendothelial migration to peritoneum or lungs was significantly lower in Eng ؉/؊ than in Eng ؉/؉ mice. Leukocyte transmigration through cell monolayers of endoglin transfectants was clearly enhanced in the presence of endoglin. Coating transwells with the RGD-containing extracellular domain of endoglin, enhanced leukocyte transmigration, and this increased motility was inhibited by soluble endoglin. Leukocytes stimulated with CXCL12, a chemokine involved in inflammation, strongly adhered to endoglincoated plates and to endoglin-expressing endothelial cells. This endoglin-dependent adhesion was abolished by soluble endoglin, RGD peptides, the anti-integrin ␣5␤1 inhibitory antibody LIA1/2 and the chemokine receptor inhibitor AMD3100. These results demonstrate for the first time that endothelial endoglin interacts with leukocyte integrin ␣5␤1 via its RGD motif, and this adhesion process is stimulated by the inflammatory chemokine CXCL12, suggesting a regulatory role for endoglin in transendothelial leukocyte trafficking. (Blood. 2013;121(2):403-415) IntroductionThe vascular endothelium controls the transit of white blood cells into and out of the bloodstream. The migration of leukocytes involves the adhesive interaction of cell surface receptors with ligands expressed on endothelial cells in a process regulated by inflammatory stimuli. Stromal-derived factor 1 (SDF1␣), renamed CXCL12, is a potent chemoattractant for a variety of cells including lymphocytes, monocytes, dendritic cells, and hematopoietic stem cells. 1 CXCL12 and its receptor CXCR4 play relevant roles in immune and inflammatory responses, including leukocyte migration and recruitment, as well as integrin-dependent adhesion and transendothelial migration. 1 CXCL12 is a critical activator of endothelial progenitors by inducing a proangiogenic phenotype and increasing migration and rolling mediated by ␣4 and ␣M integrin subunits. 2 The process of leukocyte migration through the endothelial cell monolayer involves an interaction between leukocytes' integrins and endothelial-cell receptors, both acting as adhesion molecules. Integrins most relevant to leukocytes belong to the ␤ 1 -integrin and the ␤ 2 -integrin subfamilies. Classic chemoattractants and chemokines are the most powerful physiologic activat...

Nodal tumor-forming accumulations of plasmacytoid monocytes/interferon-producing cells (PMs/IPCs) have been described in patients with myeloproliferative disorders. Here we report a series of 9 additional cases of such association. The patients were predominantly adult (median, 62 years), males (male/female ratio, 7:2), who presented with chronic myelomonocytic leukemia (4 cases), acute myeloid leukemia (1), acute monocytic leukemia (2), unclassifiable chronic myeloproliferative (1), or myeloproliferative/myelodysplastic disease (1). The prognosis was poor (median survival, 24 months) and related to progression of the underlying myeloid neoplasm. We found that in addition to lymph nodes, PMs/IPCs accumulated to bone marrow (8 cases) and skin (4 cases). Immunohistochemical markers typically expressed by PMs/IPCs (CD68, CLA/HECA452, CD123) were found in all cases and shown useful to identify cells with variations from classic morphology. In addition, PMs/IPCs expressed the interferon-alpha (IFN-alpha) inducible protein MxA, the B-cell oncogene TCL1, and granzyme B. The biologic and clinical significance of the association between PMs/IPCs and myeloid disorders remains not clarified. Using fluorescence in situ hybridization analysis in a case known to harbor monosomy 7 in the myeloid leukemia, we demonstrated that PMs/IPCs share the same chromosomal abnormality, thus indicating that they are clonal, neoplastic in nature, and closely related to the associated myeloid tumor. Recently, a novel CD56+ hematologic neoplasm has been reported and retained to stem from PMs/IPCs. The majority of PMs/IPCs in the present series failed to express CD56, thus indicating that variants of PMs/IPCs neoplasms exist, which might represent parts of a spectrum.