Abstract
Dendritic cells (DC) play a pivotal role as antigen presenting cells (APC) and their maturation is crucial for effectively eliciting an antigen-specific immune response. The p41 splice variant of MHC class II-associated chaperone, called invariant chain p41 Ii, contains an amino acid sequence, the p41 fragment, which is a thyropin-type inhibitor of proteolytic enzymes. The effects of exogenous p41 fragment and related thyropin inhibitors acting on human immune cells have not been reported yet. In this study we demonstrate that exogenous p41 fragment can enter the endocytic pathway of targeted human immature DC. Internalized p41 fragment has contributed to the total amount of the immunogold labelled p41 Ii-specific epitope, as quantified by transmission electron microscopy, in particular in late endocytic compartments with multivesicular morphology where antigen processing and binding to MHC II take place. In cell lysates of treated immature DC, diminished enzymatic activity of cysteine proteases has been confirmed. Internalized exogenous p41 fragment did not affect the perinuclear clustering of acidic cathepsin S-positive vesicles typical of mature DC. p41 fragment is shown to interfere with the nuclear translocation of NF-κB p65 subunit in LPS-stimulated DC. p41 fragment is also shown to reduce the secretion of interleukin-12 (IL-12/p70) during the subsequent maturation of treated DC. The inhibition of proteolytic activity of lysosomal cysteine proteases in immature DC and the diminished capability of DC to produce IL-12 upon their subsequent maturation support the immunomodulatory potential of the examined thyropin from p41 Ii.
Highlights
Dendritic cells (DC) function as professional antigen-presenting cells (APC) that link the innate and adaptive immune responses against invading pathogens
Confocal images of mature DC revealed that endogenous p41 Ii-specific fluorescence signal was abolished in strongly LAMP2+ CD68+ human-leukocyte antigen-DM (HLA-DM)+ and weakly HLA-DR+ vesicles clustered near the nucleus and containing the majority of all three labelled cathepsins (Fig 2)
It was reported that endogenous p41 Ii serves as a chaperone to help maintain a pool of mature cathepsin L in late-endocytic compartments of mouse bone marrow-derived macrophages [42]
Summary
Dendritic cells (DC) function as professional antigen-presenting cells (APC) that link the innate and adaptive immune responses against invading pathogens. More recent kinetic studies, performed with an expanded list of isolated recombinant cysteine proteases, have indicated that the p41 isoform of Ii, with its inhibitory thyropin segment, might play a wider role than previously thought [38], i.e., by affecting, in addition, other (endogenous) lysosomal cysteine cathepsins inside the APC, the site of p41 Ii original expression. The latter has not been further investigated in cells and not in human DC in particular. We report that cysteine protease activity within the endocytic pathway of human immature DC is diminished on successful internalization of an exogenous thyropin inhibitor and that p41 fragment reduces the secretion of interleukin-12 during the subsequent maturation of treated DC
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
