TCR/CD3 is a complex of eight subunits that after antigen stimulation initiates a series of biochemical processes in the T cell leading to changes in cell activity . Performing the appropriate effector functions by T cells allows the specific structure in which there are two functionally distinct parts: the polymorphic region , used to recognize a specific antigen receptor ( TCR) , and a region highly conservative in signal transduction mediated T cell activation ( CD3 complex ) .