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Simultaneous Study of the Recruitment of Monocyte Subpopulations Under Flow In Vitro
Published on: November 26, 2018
Activity and subcellular distribution of cathepsins in primary human monocytes
Andrea Greiner1, Alfred Lautwein, Herman S Overkleeft
1Department of Medicine II, University of Tübingen, Ob dem Himmelreich 7, 72074 Tübingen, Germany.
Insights
Active cathepsins (Cat) in human monocytes are key for antigen presentation. Novel tools revealed CatS, -B, and -H activity in lysosomes and late endosomes, crucial for major histocompatibility complex class II function.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Cathepsins (Cat) are crucial for antigen processing and MHC class II function in antigen-presenting cells (APCs).
- The specific active Cat enzymes and their subcellular localization within primary human APCs, like monocytes, remain largely uncharacterized.
- Understanding these details is vital for elucidating antigen presentation pathways.
Purpose of the Study:
- To investigate the active Cat profile and subcellular distribution in primary human peripheral blood monocytes.
- To compare Cat activity and localization in primary monocytes versus human myelo-monocytoid cell lines.
- To understand the role of Cat in the late endosome compartment for MHC class II function.
Main Methods:
- Utilized novel chemical tools for activity-dependent visualization of Cat.
- Analyzed Cat expression and activity in primary human monocytes.
- Examined subcellular localization of active Cat using microscopy and co-localization studies.
Main Results:
- Primary human monocytes exhibited active CatS, -B, and -H, with CatL being absent.
- Cat expression and activity patterns differed between primary monocytes and cell lines.
- Active Cat predominantly localized to lysosomes, with CatS also found in late endosomes, co-localizing with MHC class II components and cystatin C.
Conclusions:
- Primary human monocytes possess a distinct set of active Cat enzymes essential for antigen presentation.
- Late endosomes in monocytes harbor a controlled proteolytic environment, distinct from lysosomes, involving CatS.
- This Cat-mediated machinery in late endosomes is critical for optimal major histocompatibility complex class II function.
Abstract:
Cathepsins (Cat) in antigen presenting cells (APC) control antigen processing as well as major histocompatibility complex class II transport and function. The set of active Cat and the subcellular architecture of the class II antigen presentation compartment are largely unknown in primary human APC, including peripheral blood monocytes. We used novel chemical tools to visualize Cat in an activity-dependent manner. Primary human monocytes contained active CatS, -B, and -H, while CatL was absent. Expression and activity patterns of Cat in human myelo-monocytoid cell lines were distinct from those found in primary cells. On a subcellular scale, the bulk of active Cat was concentrated in lysosomes in primary monocytes. In late endosomes, only active CatS was found in sizable amounts, colocalizing with C-terminal processing of the class II invariant chain and with cystatin C, the major endogenous Cat inhibitor. Late endosomes of human peripheral blood monocytes contain a well-controlled proteolytic machinery distinct from lysosomes, which is likely to play a key role in class II function.
