Key Points
MHC II ubiquitination impacts dendritic cell numbers and phenotype.
MHC II ubiquitination is critical for Ag-dependent T cell responses in vivo.
MHC II ubiquitination is required for Ab responses.
Visual Abstract
Abstract
MHC class II (MHC II) Ag presentation by dendritic cells (DCs) is critical for CD4+ T cell immunity. Cell surface levels of MHC II loaded with peptide is controlled by ubiquitination. In this study, we have examined how MHC II ubiquitination impacts immunity using MHC IIKRKI/KI mice expressing mutant MHC II molecules that are unable to be ubiquitinated. Numbers of conventional DC (cDC) 1, cDC2 and plasmacytoid DCs were significantly reduced in MHC IIKRKI/KI spleen, with the remaining MHC IIKRKI/KI DCs expressing an altered surface phenotype. Whereas Ag uptake, endosomal pH, and cathepsin protease activity were unaltered, MHC IIKRKI/KI cDC1 produced increased inflammatory cytokines and possessed defects in Ag proteolysis. Immunization of MHC IIKRKI/KI mice identified impairments in MHC II and MHC class I presentation of soluble, cell-associated and/or DC-targeted OVA via mAb specific for DC surface receptor Clec9A (anti-Clec9A-OVA mAb). Reduced T cell responses and impaired CTL killing was observed in MHC IIKRKI/KI mice following immunization with cell-associated and anti-Clec9A-OVA. Immunization of MHC IIKRKI/KI mice failed to elicit follicular Th cell responses and generated barely detectable Ab to anti-Clec9A mAb-targeted Ag. In summary, MHC II ubiquitination in DCs impacts the homeostasis, phenotype, cytokine production, and Ag proteolysis by DCs with consequences for Ag presentation and T cell and Ab-mediated immunity.
Footnotes
This work was supported by Department of Health Australia, National Health and Medical Research Council grants or fellowships 1058193, 1113293, 1154502, and 1163090 (to J.A.V.) and 1161101 and 1129672 (to J.D.M.), Department of Education and Training, Australian Research Council (ARC) grants or fellowships 160103134, 170102471, and 190102213 to J.A.V. and 190101242, 180100844, 160101373, and 180100521 (to J.D.M.), a Human Frontiers Science Program grant (0064/2011 to J.A.V.), and the Australian Government’s National Health and Medical Research Council Victorian State Government Operational Infrastructure Support and the Independent Research Institutes Infrastructure Support Scheme. L.E.E.-M. was supported by the Russell and Mab Grimwade Miegunyah Fund, funded at the University of Melbourne, which supplied a Grimwade Fellowship, and an ARC Discovery Early Career Researcher Award Fellowship (ARC, DE180100418).
The online version of this article contains supplemental material.
Abbreviations used in this article
- BMDC
- bone marrow–derived DC
- cDC
- conventional DC
- CTV
- CellTrace Violet
- CTVhi
- splenocytes pulsed with OVA257–264 and labeled with a high concentration of CTV
- CTVlo
- splenocytes labeled with a low concentration of CTV
- DC
- dendritic cell
- gMFI
- geometric mean fluorescence intensity
- MARCH
- membrane-associated RING-CH-type finger
- MHC I
- MHC class I
- MHC II
- MHC class II
- pMHC II
- peptide-loaded MHC II
- TFH
- T follicular helper
- WT
- wild-type
- Received December 18, 2020.
- Accepted August 17, 2021.
- Copyright © 2021 by The American Association of Immunologists, Inc.
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