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Conditional NKT Cell Depletion in Mice Reveals a Negative Feedback Loop That Regulates CTL Cross-Priming
Christoph Heuser-Loy1, Ann-Kathrin Baumgart1, Carl-Philipp Hackstein1
1Institute of Molecular Medicine and Experimental Immunology, University Hospital Bonn, Rhenish Friedrich Wilhelm University, Bonn, Germany.
Abstract:
NKT cells are unconventional T cells whose biological role is incompletely understood. Similar to TH cells, activated NKT cells can cause dendritic cell (DC) maturation, which is required for effective CTL responses. However, it is unclear whether and how NKT cells affect CTLs downstream of the DC maturation phase. This is partially due to the lack of techniques to conditionally deplete NKT cells in vivo. To overcome this problem, we have developed two approaches for this purpose in mice: the first is based on mixed bone marrow chimeras where Jα18 knockout and depletable CD90 congenic bone marrow is combined, and the second used PLZFCre × iDTR bone marrow chimeras, which target innate-like T cells. Using these tools, we found that NKT cell depletion at 20 h, that is, after initial DC activation, did not render CTLs helpless, as CD40L signaling by non-NKT cells sufficed. Instead, NKT cell depletion even augmented CD8 T cell expansion and cytotoxicity by mechanisms distinct from reduced STAT6 signaling. These findings revealed a negative feedback loop by which NKT cells control CTL cross-priming downstream of DC maturation. The techniques described in this study expand the toolbox to study NKT cells and other unconventional T cell subsets in vivo and uncovered a hidden immunoregulatory mechanism.
Insights
Natural killer T (NKT) cells negatively regulate T cell responses. New methods to deplete NKT cells reveal they suppress CD8 T cell expansion and cytotoxicity, uncovering a feedback loop in adaptive immunity.
Area of Science:
- Immunology
- Cellular Biology
- T cell immunology
Background:
- The precise role of Natural Killer T (NKT) cells in adaptive immunity, particularly in regulating cytotoxic T lymphocyte (CTL) responses downstream of dendritic cell (DC) maturation, remains incompletely understood.
- Existing research highlights NKT cells' ability to promote DC maturation, a crucial step for effective CTL priming, but their later-stage influence on CTLs is unclear.
- A significant limitation in studying NKT cell function in vivo has been the lack of precise methods for their conditional depletion.
Purpose of the Study:
- To develop and utilize novel in vivo techniques for the conditional depletion of NKT cells in mice.
- To investigate the impact of NKT cell depletion on CTL responses after the initial DC activation phase.
- To elucidate the mechanisms by which NKT cells regulate CTL cross-priming and identify potential negative feedback loops in immune regulation.
Main Methods:
- Development of two distinct mouse models for conditional NKT cell depletion: mixed bone marrow chimeras (Jα18 knockout combined with depletable CD90 congenic bone marrow) and PLZF-Cre × iDTR bone marrow chimeras targeting innate-like T cells.
- In vivo depletion of NKT cells at 20 hours post-DC activation to assess downstream effects on CTL responses.
- Analysis of CD8 T cell expansion, cytotoxicity, and underlying signaling pathways (e.g., CD40L, STAT6) following NKT cell manipulation.
Main Results:
- Conditional NKT cell depletion, even after initial DC activation, did not impair CTL responses, as CD40L signaling from non-NKT cells was sufficient.
- Depletion of NKT cells led to augmented CD8 T cell expansion and enhanced cytotoxicity.
- These stimulatory effects on CTLs were mediated by mechanisms independent of reduced STAT6 signaling, suggesting novel regulatory pathways.
Conclusions:
- NKT cells exert a negative regulatory effect on CTL cross-priming downstream of DC maturation, establishing a previously unrecognized feedback loop.
- The developed conditional depletion techniques provide valuable tools for studying NKT cells and other unconventional T cell subsets in vivo.
- These findings reveal a hidden immunoregulatory mechanism by which NKT cells control the magnitude and efficacy of CTL responses.
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