Grafting of triggering sites onto lymphocytes. Requirement of multivalency in the stimulation of dinitrophenyl‐modified thymocytes by anti‐dinitrophenyl antibody

N⁴‐Dinitrophenyl‐L‐2,4‐diaminobutyric acid hydrazide was coupled to aldehyde groups generated by periodate oxidation of sialyl residues on thymocytes. Anti‐2,4‐dinitrophenyl(Dnp)antibody was found to stimulate mature, hydrocortisone‐resistant thymocytes, while it had no mitogenic effect on the immature thymocytes. In order to study the involvement of different regions of the antibody molecule in the triggering process of stimulation, the mitogenicity of various antibody fragments was also assessed. The divalent F(ab')₂ was found to be a superior mitogen compared to the intact antibody when added to Dnp‐conjugated thymocytes. The monovalent Fab' and Fab fragments have no mitogenic activity indicating that cross‐linkage may be a prerequisite for stimulation.