The mitogenic lectin from Phaseolus vulgaris does not recognize the T3 antigen of human T lymphocytes.
Human peripheral blood T lymphocytes are stimulated to grow and divide by lectins such as concanavalin A (Con A) and Phaseolus vulgaris phytohemagglutinin (PHA), as well as a few anti-T cell monoclonal antibodies. The latter antibodies recognize the T3 antigen. It has been suggested previously that PHA and Con A mediate T cell growth by interacting with T3. However, as reported in this study, affinity chromatography on immobilized lectins, and immunoprecipitation by lectin plus anti-lectin antibodies showed that T3 binds Con A but not PHA. Fab fragments of a monoclonal antibody against T3 (namely Leu-4) inhibited T lymphocyte proliferation induced by T3 antibodies and Con A, but not by PHA. Nevertheless, co-capping experiments performed with fluorescein-labeled lectins and rhodamine-labeled T3 antibodies showed that T3 co-caps with Con A and PHA receptors, although the co-capping with PHA was incomplete. Since the T cell receptor for antigen (Ti) has been shown to co-cap with T3 on the cell surface, we reasoned that PHA induced capping of the T3 antigen by interacting with Ti. A disulfide-linked heterodimer comprising subunits of about 49 000 and 41 000 mol. wt. that resembled the Ti molecule was detected in PHA-anti-PHA immunoprecipitates of various surface- and biosynthetically-labeled T cells, by two-dimensional (nonreduced vs. reduced) sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis. The results suggest that PHA triggers T lymphocytes by interacting with the carbohydrate moieties of Ti and imply that T lymphocytes can be stimulated by mitogens via at least two different cell surface molecules (Ti and T3).
D000911:Antibodies, Monoclonal; D000954:Antigens, Surface / Q000276:immunology*; D002846:Chromatography, Affinity; D003208:Concanavalin A / Q000276:immunology; D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D007152:Immunologic Capping; D008213:Lymphocyte Activation; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000276:immunology; D008970:Molecular Weight; D010835:Phytohemagglutinins / Q000276:immunology*; D011952:Receptors, Concanavalin A / Q000276:immunology; D011975:Receptors, Mitogen / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*
D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D006023:Glycoproteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D010835:Phytohemagglutinins; D011952:Receptors, Concanavalin A; D011975:Receptors, Mitogen; D003208:Concanavalin A