Is CD26/dipeptidyl peptidase IV a really important molecule in T cell activation of a certain rat strain?

A new monoclonal antibody (MS-7 mAb) was raised to investigate the real role of the membrane-associated molecule CD26/dipeptidyl peptidase IV (DPP IV; EC 3.4.14.5), which transduces activation signals in T cells. A strain of rats which is deficient in DPP IV was used. MS-7 mAb recognized DPP IV (110 kDa) and its 60 kDa fragment, starting at the 281st residue corresponding to the extracellular one comprising the active-site sequence Gly-X-Ser631-X-Gly of DPP IV. MS-7 mAb recognized CD26 on T cells of DPP IV+ rats both before and after mitogen activation. CD26 expression and DPP IV enzyme activity are increased on T cells following their activation; nevertheless, no CD26 was expressed on T cells of DPP IV- rats, and no DPP IV enzyme activity was detected either before or after mitogen activation. In addition, MS-7 mAb inhibited the mitogen-stimulated proliferation of DPP IV+ rats, but did not affect that of DPP IV- rats. These results suggest that CD26/DPP IV is not a necessary molecule in T cell activation, and that there is some other bypass in T cell activation of DPP IV- rats.