HTLV-1 infection in vitro induced the expression of KIR3DL2 by CD4⁺ T cells (representative assay). (A) Cell-free HTLV-1 virions induced the expression of KIR3DL2 by CD4⁺ T cells after 7 days of culture. PBMCs from healthy donors were cultured with increasing concentrations of HTLV-1 (p19-equivalent), and KIR3DL2 cell surface expression was quantified by FC. Purified HTLV-1 virions induced KIR3DL2 expression by CD4⁺ T cells in a dose-dependent manner. (B) TAX mRNA was mostly expressed by KIR3DL2⁺ CD4⁺ lymphocytes and was not observed in KIR3DL2⁻ CD4⁺ lymphocytes, quantified using the PrimeFlow RNA assay and KIR3DL2 immunolabeling.