The CD300e surface molecule, originally termed immune receptor expressed by myeloid cells (IREM)-2, was reported to associate with the DNAX-activating protein (DAP) 12 adaptor in co-transfected cells, and is capable of signaling. In the present report, we investigated in detail the function of CD300e in monocytes and myeloid DC (mDC) freshly isolated from peripheral blood of normal blood donors. Upon engagement by an agonistic mAb, CD300e triggered an intracellular calcium mobilization and superoxide anion O À 2 production in monocytes. Activation via CD300e provided survival signals that prevented monocyte and mDC apoptosis, triggered the production of pro-inflammatory cytokines and upregulated the expression of cell surface co-stimulatory molecules in both cell types. Moreover, CD300e activation of mDC enhanced the alloreactive response of naive T cells. Overall, our data formally support the notion that CD300e functions as an activating receptor capable of regulating the innate immune response in myeloid cells.Key words: Cell activation . Cell surface molecules . DC . Monocytes
IntroductionA number of surface molecules expressed by myeloid cells are members of multigenic families that include both activating and inhibitory receptors [1,2], which contribute to establish a balance of opposite signals that control the initiation, amplitude and duration of the cell response. Activating receptors have a short cytoplasmic tail with a positively charged amino acid residue within their transmembrane region that allows their association with ITAM-bearing adaptors (e.g. DNAX-activating protein (DAP) 12, FceRIg or CD3z) [3]. Upon ligand recognition and receptor clustering, ITAM become tyrosine phosphorylated and serve as docking sites for Src homology type 2 domaincontaining protein tyrosine kinases such as ZAP-70 or Syk [4,5]. Recruitment and activation of protein tyrosine kinases and downstream effectors regulate calcium mobilization, transcriptional activation, cytokine production, migration, proliferation and/or differentiation [6]. In contrast, inhibitory receptors display a longer cytoplasmic tail characterized by the presence of ITIM. Ligand-induced clustering results in tyrosine phosphorylation of ITIM that act as docking sites for SHP-1, SHP-2 or SHIP. Upon recruitment, tyrosine phosphatases become activated and dephosphorylate key signaling mediators of activation pathways such as Syk, LAT, BLNK/SLP-76, Vav, PI3K and cytoskeletal structures, consequently downregulating the signaling cascade [6][7][8].Ã These authors share equal credit for senior authorship.
722The CD300 or immune receptor expressed by myeloid celsl (IREM) family of myeloid-associated receptors consists of at least five surface molecules that are encoded by genes located on human chromosome 17 (17q25) [9]. CD300c (CMRF-35) was the first identified but has been thus far poorly characterized [10,11]. CD300a (IRp60) was shown to associate with SHP-1 and SHP-2, delivering inhibitory signals in human NK cells, mast cells, eosinophils and granulocyt...