Differential processing of autoantigens in lysosomes from human monocyte-derived and peripheral blood dendritic cells

Area of Science:

• Immunology
• Cell Biology
• Protease Biochemistry

Background:

• Dendritic cells (DC) are crucial for initiating immunity and maintaining tolerance.
• Monocyte-derived DC (MO-DC) are commonly used in vitro, but distinct primary DC subsets exist in peripheral blood (PB-DC), such as CD1c-DC.
• The lysosomal protease composition and antigen processing machinery of PB-DC, particularly CD1c-DC, remain largely uncharacterized.

Purpose of the Study:

• To investigate the repertoire of active lysosomal proteases in primary peripheral blood CD1c-DC.
• To compare the antigen processing capabilities of CD1c-DC with in vitro-generated MO-DC using clinically relevant autoantigens.
• To elucidate the distinct proteolytic pathways employed by different human DC subsets.

Main Methods:

• Analysis of active cathepsins (Cat S, L, B) and asparagine-specific endopeptidase in CD1c-DC and MO-DC.
• Functional assessment of lysosomal extracts from CD1c-DC and MO-DC in processing myelin basic protein and myelin oligodendrocyte glycoprotein.
• Identification of dominant proteases involved in antigen processing in each DC subset.

Main Results:

• CD1c-DC showed significantly lower levels of active Cat S, L, B, and asparagine-specific endopeptidase compared to MO-DC.
• Lysosomal extracts from CD1c-DC processed myelin autoantigens more effectively in vitro than those from MO-DC.
• Antigen processing in MO-DC was primarily mediated by CatS, CatD, and asparagine-specific endopeptidase, whereas CatG dominated in CD1c-DC.

Conclusions:

• Human MO-DC and primary CD1c-DC possess distinct repertoires of active endocytic proteases.
• These differences result in distinct proteolytic pathways for processing the same autoantigens.
• Understanding these variations is crucial for comprehending DC function in immunity and tolerance.