KIR3DL1 and rheumatoid arthritis: As important determinants of NKC response, KIR profile not only affects the risk for developing RA but also modulates the special clinical feature by which RA presents in each patient for example, studies have revealed that the presence of KIR2DS2 improves responsiveness to anti-TNF-α therapy [10] and the presence of KIR2DS4 reduces RA patients’ responsiveness to methotrexate therapy [15].