Rapid cell surface expression of HTSU-IgG binding proteins is observed following different methods of immune activation of cord blood T lymphocytes.

(A) Freshly isolated CD4⁺ cord blood lymphocytes were activated by exposure to bead-immobilized anti-CD3 and anti-CD28 antibodies. Two-color flow cytometry was performed with FITC-labeled anti–rabbit IgG (Sigma) and PE-labeled anti-CD45RA antibodies (Coulter). HTSU-IgG binding assays were performed at 0, 6, 24, and 48 hours after stimulation. X-axis, binding of HTSU-IgG; y-axis, binding of anti-CD45RA antibody. (B) Kinetics of expression of HTLV-I SU binding protein following different methods of T-cell activation was determined. CD4⁺ cord blood T lymphocytes were activated by treatment with PMA and ionomycin (▵), exposure to bead-immobilized anti-CD3 and anti-CD28 antibodies (■), or by PHA and IL-2 (⋄) as described in “Materials and methods.” The amount of binding was determined prior to activation and at 6, 24, 48, 72, and 120 hours after activation. The MFI of HTSU-IgG binding - MFI of SUA-IgG binding is plotted on the y-axis. Data are a representative experiment of 3 performed.