CD4 and infection: To identify the determinants of iKIR expression on T cells, we performed multivariate stepwise regression with the following predictors: age, sex, CMV serostatus, cell phenotype (CD4, CD8), T cell differentiation status (as an ordinal), infection status (uninfected, HIV-1, HTLV-1, HCV), and iKIR (KIR2DL1, KIR2DL2/L3, KIR3DL1).