Could be a T-cell-specific adapter protein involved in the control of T-cell activation. May play a role in p56-LCK-mediated T-cell signaling. Could be involved in the regulation of responses to T-cell activation stimuli, specifically proliferation and lymphokine production. Interactions with ITK and TXK may provide important biochemical links of these two important kinases with other components in the T-cell activation machinery. Interacts with KDR (By similarity). Interacts with p56-LCK, TXK and ITK. Redistributed from cytoplasm to the plasma membrane in a T-cell activation-dependent manner. Expression limited to tissues of the immune system and, in particular, activated T-cells and natural killer cells. Expressed in the thymus, lymph node, and to a lesser extent, in the spleen and bone marrow. According to PubMed:10553045, also expressed in the lung. Up-regulated substantially after T-cell activation. Phosphorylated on tyrosine residues upon TCR-stimulation. Proliferation of SH2D2A-deficient T-cells in response to T-cell receptor (TCR)-mediated activation is significantly impaired. These activated T-cells are defective in the production of interleukin (IL)-2 and interferon gamma, but not IL-4.