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Phenotypic Profiling and Activation-Associated Expression of CD99 Ligands on Human Leukocytes
Myint Myat Thu1,2, Nuchjira Takheaw1,2, Witida Laopajon1,2
1Division of Clinical Immunology, Department of Medical Technology, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai 50200, Thailand.
Biology
|January 10, 2026
Summary
CD99 ligand expression varies across immune cells, with higher levels on NK cells and monocytes, especially after IL-2 activation. This suggests CD99 ligands indicate immune activation and subset-specific regulation.
Area of Science:
- Immunology
- Cell Biology
Background:
- The immune system is a dynamic network of cells crucial for defense and homeostasis.
- Immunophenotyping is vital for understanding immune response regulation.
Purpose of the Study:
- To systematically characterize CD99 ligand expression across diverse immune cell subsets.
- To investigate the role of CD99 ligands in immune cell activation and regulation.
Main Methods:
- Utilized conventional and high-dimensional flow cytometry for detailed immunophenotyping.
- Analyzed CD99 ligand expression on various immune cell populations, including NK cells, monocytes, and T lymphocytes.
- Assessed expression changes under resting and IL-2-activated conditions.
Main Results:
- CD99 ligands were primarily detected on NK cells and monocytes, with highest expression on non-classical monocytes and CD56 Dim NK cells.
- IL-2 activation significantly enhanced CD99 ligand expression in these subsets.
- T lymphocytes showed low basal CD99 ligand expression, increasing modestly upon activation, correlating with markers like CD69 and CD137.
Conclusions:
- CD99 ligand expression is subset-specific and dynamically regulated, particularly by IL-2.
- Elevated CD99 ligand expression, alongside activation markers, suggests a role as an indicator of immune activation.
- These findings highlight the importance of CD99 ligands in modulating immune responses.
