May function in immune system as a receptor which activates via the calcineurin/NFAT-signaling pathway the downstream cytokine gene promoters. Activates the transcription of IL-13 and TNF-alpha promoters. May be involved in the regulation of B-cell, but not T-cell, development. Overexpression activates downstream effectors without ligand binding or antibody cross-linking. No direct interaction with the B-cell antigen receptor (BCR). Interacts with SYK; probably involved in BCR signaling. Interacts with ZAP70 (By similarity). Partially recruited to lipid rafts upon BCR stimulation. Highly expressed in neutrophils, primary monocytes, mast cells, monocytic cell lines and lymphocytes. Also expressed in spleen B and T-cells, and lung. Expressed at low level in non-immune tissue. The ITAM domain displays no close similarity to any existing ITAMs, except for four conserved positions. The phosphorylated ITAM domain binds ZAP70 and SYK. N-glycosylated.