Signal Regulatory Protein (SIRPα), a Cellular Ligand for CD47, Regulates Neutrophil Transmigration

Abstract

Recent studies have demonstrated that CD47 plays an important role in regulating human neutrophil (PMN) chemotaxis. Two ligands for CD47, thrombospondin and SIRP␣, have been described. However, it is not known if SIRP-CD47 interactions play a role in regulating PMN migration. In this study, we show that SIRP␣1 directly binds to the immunoglobulin variable domain loop of purified human CD47 and that such SIRP-CD47 interactions regulate PMN transmigration. Specifically, PMN migration across both human epithelial monolayers and collagen-coated filters was partially inhibited by anti-SIRP monoclonal antibodies. Similar kinetics of inhibition were observed for PMN transmigration in the presence of soluble, recombinant CD47 consisting of the SIRP-binding loop. In contrast, anti-CD47 monoclonal antibodies inhibited PMN transmigration by markedly different kinetics. Results of signal transduction experiments suggested differential regulation of PMN migration by SIRP versus CD47 by phosphatidylinositol 3-kinase and tyrosine kinases, respectively. Immunoprecipitation followed by Western blotting after SDS-PAGE under nonreducing conditions suggested that several SIRP protein species may be present in PMN. Stimulation of PMN with fMLP resulted in increased surface expression of these SIRP proteins, consistent with the existence of intracellular pools. Taken together, these results demonstrate that PMN migration is regulated by CD47 through SIRP␣-dependent and SIRP␣-independent mechanisms.

The CD300a (IRp60) inhibitory receptor is rapidly up-regulated on human neutrophils in response to inflammatory stimuli and modulates CD32a (FcγRIIa) mediated signaling

“…Human neutrophils have been shown to express other ITIM containing inhibitory receptors (Liu et al, 2002;Mingari et al, 2001;Richard et al, 2002;Skubitz et al, 2000;Verbrugge et al, 2006;Wu et al, 2005). CD305 (also known as LAIR-1) is expressed at very low levels on peripheral blood neutrophils, and its expression, like CD300a, is also up-regulated after stimulation of mature neutrophils with pro-inflammatory agents, although it is not known if the up-regulation of LAIR-1 expression is a consequence of the translocation of a pre-existing intracellular pool to the plasma membrane or new synthesis of the receptor is required (Verbrugge et al, 2006).…”

“…CD31 (or PECAM-1) (Wu et al, 2005), CD66a (or CEACAM1 or BGPa) (Skubitz et al, 2000), SIRPα (Liu et al, 2002), p75/AIRM1 and CD33 (Mingari et al, 2001) are other ITIM containing inhibitory receptors expressed on human mature neutrophils. The expression levels of these receptors are also regulated during neutrophil activation, but studies on the function of these receptors has focused more on their role in adhesion and chemotaxis of neutrophils than on the inhibition of activating signals (Liu et al, 2002;Skubitz et al, 2000;Wu et al, 2005).…”

“…The expression levels of these receptors are also regulated during neutrophil activation, but studies on the function of these receptors has focused more on their role in adhesion and chemotaxis of neutrophils than on the inhibition of activating signals (Liu et al, 2002;Skubitz et al, 2000;Wu et al, 2005). In fact, it is very important to point out that, to our knowledge, our study is the first one showing an inhibitory function for an ITIM containing receptor in mature human neutrophils.…”

Neutrophil Migration across Tight Junctions Is Mediated by Adhesive Interactions between Epithelial Coxsackie and Adenovirus Receptor and a Junctional Adhesion Molecule-like Protein on Neutrophils

“…As shown in Figure 2A, two CAR-GST recombinants (CAR1 ϩ 2-GST: AA 1-240; CAR1-GST: AA 1-134) and three JAML-Fc recombinants (JAML1-Fc: AA 1-130; JAML2-Fc: AA 141-256; JAML1 ϩ 2-Fc: AA 1-256) were prepared, accordingly. In the experiments, recombinant CD47 and SIRP␣1 extracellular domain fusion proteins CD47-alkaline phosphatase (AP) and SIRP␣-GST were produced as described previously (Seiffert et al, 1999;Liu et al, 2002Liu et al, , 2004a. …”

Respiratory innate immune proteins differentially modulate the neutrophil respiratory burst response to influenza A virus

“…These divergent effects appear to result from engagement of distinct inhibitory collectin receptors [e.g., signal inhibitory regulatory protein (SIRP)-␣] by the free collectins as opposed to activating collectin receptors (e.g., calreticulin/CD91) engaged by ligand-collectin complexes. Both SIRP␣ and calreticulin are present on neutrophils; however, their functional interactions with complexed or free surfactant collectins are unknown (8,37,38).…”