CD9 Regulates Major Histocompatibility Complex Class II Trafficking in Monocyte-Derived Dendritic Cells

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Dendritic cells (DCs) present antigens to CD4+ T cells, initiating adaptive immunity.
• Major histocompatibility complex class II (MHC-II) molecules are key for antigen presentation and are found in tetraspanin-enriched microdomains (TEMs) in DCs.

Purpose of the Study:

• To investigate the role of tetraspanin CD9 in the T cell-stimulatory capacity of dendritic cells.
• To elucidate CD9's function in MHC-II trafficking and its impact on antigen presentation.

Main Methods:

• Utilized granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent and fms-like tyrosine kinase 3 ligand (Flt3L)-dependent bone marrow-derived dendritic cells (BMDCs).
• Generated CD9 knockout (KO) BMDCs to assess the impact of CD9 deficiency.
• Analyzed T cell activation levels, MHC-II surface expression, and intracellular MHC-II localization using techniques like LAMP-1 staining.

Main Results:

• CD9 deficiency in GM-CSF-dependent BMDCs (resembling monocyte-derived DCs or MoDCs) reduced T cell activation.
• CD9 KO MoDCs exhibited decreased surface MHC-II expression due to impaired trafficking to the plasma membrane.
• MHC-II remained trapped in acidic compartments (LAMP-1 enriched) in immature CD9 KO MoDCs, and internalization/recycling were affected in mature MoDCs.

Conclusions:

• Tetraspanin CD9 specifically regulates antigen presentation in MoDCs.
• CD9 is essential for the proper intracellular trafficking of MHC-II molecules to the cell surface.
• CD9's role in MHC-II trafficking impacts the T cell-stimulatory capacity of MoDCs.