doi:10.1006/cyto.1999.0643 available online at http://www.idealibrary.com on SHORT COMMUNICATION MECHANISMS OF CD26/DIPEPTIDYL PEPTIDASE IV CYTOKINE-DEPENDENT REGULATION ON HUMAN ACTIVATED LYMPHOCYTES Francisco J. Salgado, 1 Elena Vela, 2 Margarita Martı ´n, 3 Rafael Franco, 3 Montserrat Nogueira, 1 Oscar J. Cordero 1 Among the cellular pathways activated by IL-12, we had previously found that both the percentage and intensity of CD26 + cells in the PHA-stimulated T cells increased when IL-12 was present (independently of its CD4 or CD8 phenotype). Now, we examined the molecular mechanisms of this IL-12-mediated effect. The IL-12 regulation pathway is dependent of de novo protein synthesis and independent of cytokine secretion. Our results show two transcripts for CD26 in PBMC for the first time and no regulation by ILs at this level. Furthermore, secretion of the serum forms of CD26/DPPIV were not affected by IL-12. Interestingly, assays with neutralizing mAbs against TNF- suggest that this cytokine negatively modulates CD26 expression. The fact that translation and probably translocation of CD26 toward the cell surface can be regulated by IL-12 and TNF- reveals new aspects about the control of this T H1 marker.  2000 Academic Press Dipeptidyl peptidase IV (DPPIV; CD26; EC 3.4.14.5) is a 110-kDa cell surface glycoprotein expressed on different cell types, including T cells. It is an enzyme that cleaves NH 2 -terminal dipeptides from polypeptides with either L-proline or L-alanine at the penultimate position. 1 Certain anti-CD26 mAbs are able to transmit an activating signal to the T cell and regulate immune responses. 2 Moreover, CD26 is a functional receptor for collagen and adenosine deaminase (ADA). 3,4 Despite the multifunctionality of CD26, little is understood about the involvement of these functions in the immune response. We have found a strong upregu- lation of CD26 expression and DPPIV function on human activated lymphocytes by IL-12 and IL-2, but not by IL-1, IFN-, TNF- or IL-4, 5,6 suggesting that CD26 is a marker of TH 1 responses. In view of the possibilities of IL-12 therapeutic use in cancer, immunodeficiencies, etc., 7 elucidating the molecular mechanisms of this upregulation of CD26 on human activated lymphocytes will help to clarify the immunological role of CD26. RESULTS IL-12 enhances the production of the DPPIV protein but not CD26 mRNA expression on activated lymphocytes We have previously described an IL-12-dependent CD26 upregulation in PHA blasts. 5 To test if this regulation implicates CD26 gene transcription and/or translation, Western and Northern blot analyses were performed. The expression of CD26 in 5-day blasts, cultured with or without IL-12, was investigated by immunoblotting using mAb 1F7 (anti-hCD26). Figure 1A shows three main bands, the molecular charac- teristics of which are being studied. IL-12-activated cells expressed enhanced levels of those bands. In similar conditions of activation, CD26 mRNA was quantified by Northern blotting. Interestingly, the two From the 1 Department of Biochemistry and Molecular Biology, University of Santiago de Compostela, Santiago de Compostela; 2 Department of Biochemistry and Molecular Biology, University of Barcelona, Barcelona; 3 Laboratory of Molecular Biology, Service of Pathological Anatomy, Universitary Hospital ‘‘Germans Trias i Pujol’’ of Badalona, Barcelona, Spain Correspondence to: Dr Oscar J. Cordero, Departamento de Bioquı ´mica e Bioloxı ´a Molecular, Universidade de Santiago de Compostela, Facultade de Bioloxı ´a, Campus Sur. 15706 Santiago de Compostela, Galicia, Spain; E-mail: bnojcord@usc.es Received 29 June 1999; received in revised form 29 July 1999; accepted for publication 4 November 1999  2000 Academic Press 1043–4666/00/071136+06 $35.00/0 KEY WORDS: CD26/dipeptidyl peptidase IV/hydrocortisone/ interleukin 12/tumour necrosis factor- CYTOKINE, Vol. 12, No. 7 (July), 2000: pp 1136–1141 1136