Behaves as a cytokine, promoting IL17A secretion by CD4+ T-cells, and differentiation and activation of IL17 producing helper T-cells (TH17). Inhibitory immune receptor involved in the regulation of phagocytes. Expressed on myeloid (neutrophils, eosinophils and monocytes) but not on lymphoid cells. Contains 2 copies of a cytoplasmic motif that is referred to as the immunoreceptor tyrosine-based inhibitor motif (ITIM). This motif is involved in modulation of cellular responses. The phosphorylated ITIM motif can bind the SH2 domain of several SH2-containing phosphatases. Both motives are required for full inhibition of FCER1A-mediated degranulation. Isoform 2 is N-glycosylated. Mainly detected in immune tissues and cells. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.