Transcriptional Profiling of Human Monocytes Identifies the Inhibitory Receptor CD300a as Regulator of Transendothelial Migration
Date Published: September 18, 2013
Publisher: Public Library of Science
Author(s): Sharang Ghavampour, Carsten Lange, Cristina Bottino, Volker Gerke, Masataka Kuwana.
Local inflammatory responses are characterized by the recruitment of circulating leukocytes from the blood to sites of inflammation, a process requiring the directed migration of leukocytes across the vessel wall and hence a penetration of the endothelial lining. To identify underlying signalling events and novel factors involved in these processes we screened for genes differentially expressed in human monocytes following their adhesion to and passage through an endothelial monolayer. Functional annotation clustering of the genes identified revealed an overrepresentation of those associated with inflammation/immune response, in particular early monocyte to macrophage differentiation. Among the gene products so far not implicated in monocyte transendothelial migration was the inhibitory immune receptor CD300a. CD300a mRNA and protein levels were upregulated following transmigration and engagement of the receptor by anti-CD300a antibodies markedly reduced monocyte transendothelial migration. In contrast, siRNA mediated downregulation of CD300a in human monocytes increased their rate of migration. CD300a colocalized and cosedimented with actin filaments and, when activated, caused F-actin cytoskeleton alterations. Thus, monocyte transendothelial migration is accompanied by an elevation of CD300a which serves an inhibitory function possibly required for termination of the actual transmigration.
The inflammatory response of vascularized tissue to perturbations such as injury and infection is characterized by the recruitment of circulating leukocytes to the actual site of perturbation. In order to reach these sites, leukocytes have to penetrate the vessel wall in a directional manner. This process is governed by a cascade of interactions between leukocyte and endothelial cell surface molecules. Following inflammatory stimulation leukocytes engage in initial, primarily selectin-mediated interactions with the activated endothelium that typically lead to tight adhesive contacts mediated by integrins, whose activity is increased upon stimulation of leukocyte chemokine receptors. Finally leukocytes transverse the endothelial blood vessel lining through a paracellular, in some cases also transcellular, route that requires the activity of several endothelial adhesion molecules such as PECAM, CD99, VE-cadherin and JAM family proteins (for reviews see –).
Transendothelial migration is known to lead to changes in leukocyte biology which enable the cells to function efficiently when reaching the underlying tissue . In line with this, our functional annotation clustering analysis of genes differentially expressed in transmigrated monocytes revealed the highest enrichment score for genes associated with inflammation/immune response. Some of the differentially regulated genes have well-known functions in monocyte-mediated immune responses, such as the interleukin 1 receptor antagonist (IL1RN) (see, for example, . Others, however, are known to play a role in inflammation in general, but have not yet been characterized in monocytes. One such example is CD300a, which is an inhibitory receptor in human NK cells  and eosinophils  but is also expressed in other leukocytes and was chosen here for further analysis with respect to its potential role in monocyte transmigration.
Keywords: transcriptional profiling, monocytes, transendothelial migration
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