CYTOFLUOROGRAPHIC EVIDENCE THAT THYMOCYTE DIPEPTIDYL PEPTIDASE-IV (CD26) ACTIVITY IS ALTERED WITH STAGE OF ONTOGENY AND APOPTOTIC STATUS

CD26 is a multifunctional molecule implied to have a variety of roles in the immune response including its activity as a membrane exopeptida se (Dipeptidyl peptidase IV) which cleaves several protein molecules, In order to further define the expression and functional activity of C D26 in the developing thymus, we utilized a nondisruptive, cytofluorog enic assay which allowed simultaneous measurement of DPP IV activity w ith a fluorochrome-conjugated peptide substrate and surface staining o f the T lymphocyte Lineage antigens CD4 and CD8, Neonatal and adult mu rine thymi were examined using the three-color assay and significant d ifferences in DPP IV activity were found among the thymocyte subsets d efined by their CD4/CD8 phenotype, Single-positive cells bore higher a ctivity than CD4(-)/CD8(-) cells and neonates had higher activity than adults, Thymocytes with characteristics consistent with apoptotic cel ls expressed higher DPP IV activity, Thus, DPP IV appears to be upregu lated both as thymocytes mature and among thymocytes which are undergo ing programmed cell death, These results suggest that CD26 is ontogeni cally controlled during T cell maturation and may play a role in thymi c deletion of emerging clones. (C) 1996 Wiley-Liss, Inc.