T-lymphocytes originate in ____________ and then migrate to the ____________ to complete their maturation. They possess a unique ____________ and initially both the ____________ and CD8 proteins. Each T-lymphocyte must have its TCR "tested" to determine not only whether it is able to bind to the ____________ molecule with presented ____________ , but also whether it binds only to antigens that are ____________ . This testing results in ____________ selection.