The macrophage mannose receptor promotes uptake of ADAMTS13 by dendritic cells

Area of Science:

• Immunology
• Hematology
• Biochemistry

Background:

• ADAMTS13 regulates platelet function by cleaving VWF multimers.
• Autoantibodies against ADAMTS13 cause acquired thrombotic thrombocytopenic purpura (aTTP).
• T cell activation, involving antigen presentation by dendritic cells (DCs), is critical for autoantibody formation.

Purpose of the Study:

• To investigate the mechanism of ADAMTS13 endocytosis by immature monocyte-derived DCs.
• To identify the specific receptor(s) involved in ADAMTS13 uptake by DCs.

Main Methods:

• Flow cytometry and confocal microscopy to assess ADAMTS13 uptake.
• Use of EGTA, mannan, and blocking antibodies to inhibit endocytosis.
• siRNA silencing of the macrophage mannose receptor (MR).
• In vitro binding assays to confirm receptor-ligand interaction.

Main Results:

• Significant endocytosis of fluorescently labeled ADAMTS13 by DCs was observed.
• ADAMTS13 uptake was blocked by EGTA and mannan, suggesting a calcium-dependent lectin pathway.
• The macrophage mannose receptor (MR) was identified as a key receptor mediating ADAMTS13 endocytosis.
• siRNA silencing of MR reduced ADAMTS13 uptake, confirming MR's role.
• Direct binding of ADAMTS13 to the carbohydrate recognition domains of MR was confirmed.

Conclusions:

• ADAMTS13 is efficiently endocytosed by DCs via the macrophage mannose receptor (MR).
• Carbohydrate moieties on ADAMTS13 are involved in its interaction with MR.
• This MR-mediated endocytosis pathway is a critical step in the immune response leading to aTTP.