CD28 and rheumatoid arthritis: Studies by Yen et al. [27, 28], Ramirez [5] (in the Mexican population), and Majorczyk [29] (in western European population) have all confirmed the higher frequency of both KIR2DL2 and 2DS2 and also the functionality of KIR2DS2 expressing CD28-null T-cells in RA pathology.