Lectin interactions with the Jurkat leukemic T-cell line: quantitative binding studies and interleukin-2 production

Phytohemagglutinin (PHA), concanavalin A (Con A), pea lectin, and wheat germ agglutinin (WGA) have been used to investigate their binding properties to Jurkat 77 6.8 leukemic human T cells and their ability to induce these cells to produce interleukin-2 (IL-2). Binding studies showed that the Jurkat cells fixed 0.82 +/- 0.11 microgram pea lectin, 2.02 +/- 0.17 micrograms Con A, 1.85 +/- 0.07 micrograms PHA and 8.88 +/- 0.61 micrograms WGA. Scatchard plots were linear, indicating that the binding process was homogeneous with respect to the binding constant. PHA and Con A bound with the highest affinity [Kass (apparent) approximately equal to 9 x 10(9) M-1], followed by pea lectin and WGA [Kass (apparent) approximately equal to 3 x 10(9) M-1]. The number of lectin binding sites was in agreement with the results of saturation experiments. We also evaluated the effect of the presence of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the binding process. Results show that there were no gross alterations in the value of (apparent) Kass in the case of PHA and WGA. In contrast, the presence of TPA decreased the affinity of Con A and modified the Scatchard profile for pea lectin, which was curvilinear with a concavity turned upward. In this case, data were (apparent) K1 = 17.7 x 10(9) M-1 ("high-affinity" sites) and (apparent) K2 = 2.6 x 10(9) M-1 ("low-affinity" sites). The four lectins shared the ability to stimulate Jurkat 77 6.8 cells to secrete IL-2. Optimal lectin concentrations were 20 micrograms/ml (PHA) and 50 micrograms/ml (WGA and Con A). Pea lectin failed to display a dose-response relationship, and IL-2 production increased proportionally with lectin concentration. Con A was the most efficient stimulator (250 U/ml), followed by WGA (160 U/ml) and PHA (108 U/ml). Addition of TPA potentiated Jurkat cell response. In this case, Con A and pea lectin were the most efficient stimulators (470 U/ml), followed by PHA (316 U/ml) and WGA (271 U/ml). Here, also, pea lectin failed to show a dose-response relationship. Our data do not reveal an obvious relationship between the binding parameters and the ability of the lectins to induce IL-2 production. We suggest that the efficiency of the four lectins to stimulate IL-2 production in the case of the Jurkat 77 6.8 variant is most likely related to the nature of their specific cell surface receptor(s).