An adapter protein which plays a role in the regulation of immunoreceptor signaling, including PLC-gamma-mediated B-cell antigen receptor (BCR) signaling and FC-epsilon R1-mediated mast cell degranulation (By similarity). Together with FGR, it acts as a negative regulator of natural killer cell-activating receptors and inhibits interferon-gamma production (By similarity). Acts as a positive regulator of both T-cell receptor and natural killer T (NKT) cell receptor signaling in CD4-positive NKT cells (By similarity). Together with MAP4K1, it enhances CD3-triggered activation of T-cells and subsequent IL2 production (By similarity). May be involved in tumor necrosis factor induced cell death by promoting reactive oxidative species generation, and MLKL oligomerization, ultimately leading to necrosis (By similarity). Involved in phosphorylation of LAT (By similarity). May be involved in high affinity immunoglobulin epsilon receptor signaling in mast cells (By similarity).