Expressions and inhibitory functions of CD300a receptors on purified human basophils

Abstract

The inhibitory myeloid immunoglobulin receptor CD300a (IRp60) has been shown to downregulate mast cell and eosinophil activities, thereby serving as a potential target for inhibiting allergic effector cell input in allergy. Our aims were to study the expression and functional properties of this receptor in purified human basophils, cells that crucially contribute to Th2-type immunity and allergy. Basophils homogeneously expressed CD300a as well as the inhibitory receptor CD200R on their cell surface, and these expressions increased after anti-IgE stimulation. IgE-mediated basophil degranulation was also significantly inhibited by crosslinking of either CD200R or CD300a (by 90% and 50%, respectively). Inhibitory SHIP-1 phosphorylations were also induced by CD200R and CD300a, although they were not noticeably increased by IgE-dependent activation. We conclude that both CD200R and CD300a play a role in reducing IgE-mediated basophil function and may crucially govern the known differential activities of these cells in vivo.

The Biology and Disease Relevance of CD300a, an Inhibitory Receptor for Phosphatidylserine and Phosphatidylethanolamine

“…Furthermore, immunoprecipitation of CD300a from human mast cells that were treated with Kit-CD300a, a bispecific Ab fragment linking Kit with CD300a, induced its tyrosine phosphorylation and the recruitment of SHIP but not SHP-1 (53). Triggering of CD300a with mAbs induced weak phosphorylation of SHIP-1 on human basophils, but the phosphorylation status of SHP-1 and SHP-2 was not tested (21). In a mouse B cell line, coligation of the BCR with anti-mouse IgG and Fc-CD300a, a chimeric molecule consisting of the extracellular and transmembrane domains of FcgRIIB and the cytoplasmic domain of mouse CD300a, resulted in the association of the intracellular tail of CD300a with SHP-1, SHP-2, and SHIP (30).…”

“…Naive B cells express low levels of CD300a, whereas memory B cells and plasma cells express variable levels, and germinal center B cells are negative for CD300a cell surface expression (16). In the myeloid lineage, CD300a is detected on the surface of plasmacytoid dendritic cells (pDCs), myeloid dendritic cells (mDCs), monocytes, macrophages, neutrophils, eosinophils, basophils, and mast cells (13,(18)(19)(20)(21)(22)(23)(24)(25).…”

“…In neutrophils, LPS and GM-CSF treatment caused a rapid translocation of an intracellular pool of CD300a to the cell surface, contributing to the observed increased expression in response to those stimuli (18). It is quite conceivable that an intracellular pool of CD300a also exists in basophils, which translocates to the cell surface in ,20 min upon cell stimulation through FceRI (21,25). In eosinophils, CD300a expression is also upregulated by hypoxia and GM-CSF, and the inhibition of hypoxia-inducible factor 1 abolished this upregulation (24).…”

“…Hence, its engagement by agonist mAbs decreased NK cell-mediated cytotoxicity and inhibited IgE-dependent Ca 2+ mobilization and mediator release from mast cells and SCF-mediated mast cell activation, differentiation, and survival, as well as IgEinduced basophil degranulation (9,14,19,21,25,31,53,56). The mAb-mediated cross-linking of CD300a also reduces FcgRIIa-triggered reactive oxygen species production and Ca 2+ flux in neutrophils (18), suppresses eosinophil survival, migration, and inflammatory mediator production triggered by eotaxin, IL-15, and GM-CSF (23), and LPS-and CpG-induced IL-8 secretion by myelomonocytic cell lines (55).…”

Identification of CD300a as a new hypoxia-inducible gene and a regulator of CCL20 and VEGF production by human monocytes and macrophages

“…[13][14][15][16][17][18][19][20][21] CD300a plays a role in the regulation of immune responses, acting predominantly as an inhibitory receptor. Its engagement by an agonist mAb decreases NK cell cytotoxicity, 14,22 inhibits IgE-induced mast cell and basophil degranulation, 17,21 T-cell proliferation and IFNg secretion, 19 and B-cell receptor-mediated signaling, 20 reduces FcgRIIatriggered reactive oxygen species production and Ca 2+ flux in neutrophils, 16 and suppresses eosinophil survival, migration and inflammatory mediator production triggered by eotaxin, IL-5 and granulocyte macrophage colony-stimulating factor. 18 Furthermore, in vivo studies in mice with bispecific Abs have shown that CD300a triggering can reverse tissue remodeling and airway inflammation in a model of asthma, 23 and abrogate IgE-mediated allergic reactions 17 and stem cell factorinduced cutaneous anaphylaxis.…”