CD28 and rheumatoid arthritis: Central memory (CM) T cells were defined by CCR7+ CD45RO+ CD28+ Fas+, transitional memory (TM) by CCR7– CD45RO+ CD28+ Fas+, effector memory (EM) by CCR7– CD45RO+ CD28– Fas+, terminal effector (TE) by CCR7– CD45RO+/– Fas–, and effector memory RA (EMRA) by CCR7– CD45RO– CD45RA+ Fas+/–.