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High levels of functional endopeptidase 24.11 (CD10) activity on human thymocytes: preferential expression on
B Mari1, J P Breittmayer, S Guerin
1INSERM U364, Faculté de Médecine, Nice, France.
Insights
Human thymocytes express functional neutral endopeptidase (NEP), also known as CD10. This enzyme plays a key role in the maturation of human thymocytes, particularly immature CD4- CD8- cells.
Area of Science:
- Immunology
- Enzymology
- Cell Biology
Background:
- Immune cells express exopeptidases, but surface peptidases on human thymocytes are poorly understood.
- CD10, an enzyme, has been investigated for its presence and function on human thymocytes.
Purpose of the Study:
- To identify and characterize CD10 (neutral endopeptidase, NEP) on human thymocytes.
- To investigate the role of NEP in human thymocyte maturation.
Main Methods:
- Flow cytometry (FACS) and enzymatic assays were used to analyze CD10 expression.
- Specific NEP inhibitors (thiorphan, retrothiorphan, phosphoramidon) were employed.
- High-performance liquid chromatography (HPLC) was used to assess enzyme activity on thymopentin.
Main Results:
- Human thymocytes exhibit significant CD10-specific enzymatic activity, hydrolyzing NEP substrates.
- CD10 activity was inhibited by specific NEP inhibitors.
- NEP hydrolyzed thymopentin, a factor involved in thymocyte maturation.
- CD10/NEP was primarily found on immature thymocyte subsets (CD3-, CD3low, CD4- CD8-).
Conclusions:
- Human thymocytes express functional neutral endopeptidase (NEP/CD10).
- NEP is associated with immature thymocyte populations.
- NEP likely plays a role in human thymocyte maturation.
Abstract:
Although it is now well established that cells of the immune system express most of the exopeptidases described so far, little information is available concerning the identification and the characterization of the peptidases associated with the surface of human thymocytes. In the present study we have focused on CD10 expression on thymocytes using both FACS and enzymatic analysis. Unfractionated intact human thymocytes were shown to express significant levels of CD10-specific enzymatic activity, as assessed by the hydrolysis of the neutral endopeptidase (NEP) substrate Suc-Ala-Ala-Phe-pNA and of D-Ala2-Leu-enkephalin, a typical NEP substrate. CD10 activity was abolished by specific NEP inhibitors, including thiorphan, retrothiorphan and phosphoramidon. Moreover, high performance liquid chromatography (HPLC) analysis showed that intact thymocytes and purified NEP hydrolysed thymopentin, a thymic factor known to induce the maturation of prothymocytes into thymocytes. Finally, CD 10/NEP was preferentially associated with CD3- CD3low and immature CD4- CD8- thymocytes. The data demonstrate for the first time that human thymocytes express functional NEP and suggest a role for this enzyme in the maturation of human thymocytes.