CD4 and viral infectious disease: We found that iKIR expression increased significantly according to the cell differentiation stage (P = 4 × 10–14), was higher for KIR2DL2/L3 than for KIR2DL1 (P = 4 × 10–12), and was higher for CD8+ T cells than for CD4+ T cells but was not significantly increased by viral infection (either when considered separately or when pooled to increase the power) (Figure 2 and Supplemental Tables 1 and 2).