Murine thymocytes possess specific cell surface‐associated exoaminopeptidase activities: Preferential expression by immature CD4⁻CD8⁻ subpopulation

Abstract

Murine thymocytes are shown to possess at least three well-defined exo-N-aminopeptidase activities on their surface. One of them cleaves the prolyl bond in the synthetic dipeptide nitroanilide Gly-Pro-pNA (Km 0.95 mM and Vmax 8 nmol/h at pH 7.4 and 37 degrees C) and is specifically inhibited by phenylmethane sulfonyl fluoride, diprotin A, Gly-Pro-Ala and Gly-Pro-Gly-Gly. These data further support identification of this enzyme with a serine exopeptidase dipeptidyl peptidase IV (DPP IV), previously reported to be specific for collagen. The two other forms of N-exopeptidase activities are detected when Ala-pNA and Leu-pNA are used as substrates. Leu-aminopeptidase activity (Km 1.4 mM, Vmax 15 nmol/h) and Ala-aminopeptidase activity (Km 4.0 mM, Vmax 20 nmol/h) are inhibited by inhibitors for thiol- and trypsin-like proteinases, i.e. tosyl lysyl chloromethyl ketone, leupeptin and N-ethylmaleimide. Addition inhibition of Leu-aminopeptidase activity by peptstatin, a known inhibitor of carboxyl proteases, suggests that aminopeptidase activity detected with Leu-pNA is different in part from Ala-aminopeptidase activity. Among the various lymphoid cell populations tested, the three aminopeptidase activities are increased by three- to fourfold in the immature CD4-CD8- thymocyte subset as well as in the thymoma BW5147. In contrast, cortisone-resistant thymocytes, lymph node and spleen cells exhibit levels of activities almost similar to that of unfractionated thymocytes. During ontogeny, the levels of these activities are increased four- to sevenfold on fetal thymocytes (from days 14 to 16). Finally, when thymocytes or spleen cells are cultured with a mitogenic concentration of concanavalin A, their proliferative responses are correlated with an enhancement of the aminopeptidase activities (1.3- to 5-fold). From these results, a correlation between the presence of these peptidases on the cell surface of immature and mature lymphoid cells and biological responsiveness is suggested.

Glucocorticoid agonistic and antagonistic effects of mifepristone and onapristone on thymocyte subset composition and CD26/dipeptidyl peptidase IV activity in infant male rats

“…Fig. 6A and B confirm the findings of Bauvois [21] and Bristol et al [22] that, while all stages of thymocyte differentiation are CD26-positive, the earliest CD4 − CD8 − precursors bear the highest amount of CD26 on their surface (Fig. 6A).…”

CD26 expression and dipeptidyl peptidase IV activity in an aggressive hepatosplenic T-cell lymphoma

“…In this regard, CD26 has been demonstrated to be a participant in a variety of immunological functions, including costimulation during T-cell activation (16,17), antibody production (34), and as a potential regulator of T-lymphocyte ontogeny (18,19). The activity level and differentiation status of T cells appear to modify and upregulate levels of CD26, such that memory T cells or T cells undergoing activation increase both their level of expression of CD26 and their measurable DPP IV activity (15).…”

“…For example, CD26 appears to provide a ''second signal'' as a costimulatory ligand during the process of T-cell activation, thereby promoting an upregulation of IL2 gene activation (16,17). We (18) and others (19) have described CD26 as a potentially important molecule in the ontogenetic development of T cells during maturation in the murine and human thymus. Since it appears that DPP IV enzymatic activity and/or binding to ADA is prerequisite for the function of CD26 (20), we have used measurement of enzymatic activity of this molecule as an assessment of function for the molecule.…”

A trypsin‐like serine protease activity on activated human B cells and various B cell lines

“…For localization studies the method described by Bauvois was used [24] .The protocol described in Sect. 2.5 was used, with the following additional steps: (a) 5 x lo5 low-density B cells were incubated with Tos-Gly-Pro-Arg-pNA (0.5 mg/ml) at 37 "C in a final volume of 100 pl.…”