Predicted to enable identical protein binding activity and transmembrane signaling receptor activity. Involved in positive thymic T cell selection. Part of alpha-beta T cell receptor complex. Is expressed in thymus primordium. Human ortholog(s) of this gene implicated in immunodeficiency 19 and severe combined immunodeficiency. Orthologous to human CD3D (CD3d molecule). Predicted to enable several functions, including SH3 domain binding activity; identical protein binding activity; and protein heterodimerization activity. Involved in nervous system development and positive regulation of cell adhesion. Acts upstream of or within several processes, including positive regulation of T cell activation; positive regulation of cytokine production; and regulation of signal transduction. Located in several cellular components, including dendritic spine; external side of plasma membrane; and immunological synapse. Part of alpha-beta T cell receptor complex. Is expressed in colon and hemolymphoid system. Human ortholog(s) of this gene implicated in immunodeficiency 18. Orthologous to human CD3E (CD3e molecule).