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 (By similarity). May be involved in the regulation of B-cell, but not T-cell, development. No direct interaction with the B-cell antigen receptor (BCR). Interacts with SYK; probably involved in BCR signaling. Interacts with ZAP70. Partially recruited to lipid rafts upon BCR stimulation. Highly expressed in the spleen, expressed by both B- and CD4+ and CD8+ T-cells, as well as non-T- and non-B-cells, including macrophages and neutrophils. Expressed at low levels, if any, in non-immune tissue. Highest expression in pro-B-cells decreases with B-cell differentiation. 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.