Saposins modulate human invariant Natural Killer T cells self-reactivity and facilitate lipid exchange with CD1d molecules during antigen presentation

Edited by Mitchell Kronenberg, La Jolla Institute for Allergy and Immunology, La Jolla, CA, and accepted by the Editorial Board October 28, 2013 (received for review May 29, 2013)
November 18, 2013
110 (49) E4753-E4761

Significance

Understanding how to optimize lipid-loading onto CD1d molecules is important to better harness invariant natural killer T (iNKT) cells’ central role at the interface between innate and adaptive immunity. We report that the lipid transfer proteins saposins play an essential role in modulating human iNKT cell autoreactivity to antigen-presenting cells activated by inflammatory stimuli. Lipid-loading occurs in an endo-lysosomal compartment, where saposins work as “lipid editors,” capable of fine-tuning loading and unloading of CD1d molecules and increasing the off-rate of CD1d-bound lipids.

Abstract

Lipid transfer proteins, such as molecules of the saposin family, facilitate extraction of lipids from biological membranes for their loading onto CD1d molecules. Although it has been shown that prosaposin-deficient mice fail to positively select invariant natural killer T (iNKT) cells, it remains unclear whether saposins can facilitate loading of endogenous iNKT cell agonists in the periphery during inflammatory responses. In addition, it is unclear whether saposins, in addition to loading, also promote dissociation of lipids bound to CD1d molecules. To address these questions, we used a combination of cellular assays and demonstrated that saposins influence CD1d-restricted presentation to human iNKT cells not only of exogenous lipids but also of endogenous ligands, such as the self-glycosphingolipid β-glucopyranosylceramide, up-regulated by antigen-presenting cells following bacterial infection. Furthermore, we demonstrated that in human myeloid cells CD1d-loading of endogenous lipids after bacterial infection, but not at steady state, requires trafficking of CD1d molecules through an endo-lysosomal compartment. Finally, using BIAcore assays we demonstrated that lipid-loaded saposin B increases the off-rate of lipids bound to CD1d molecules, providing important insights into the mechanisms by which it acts as a “lipid editor,” capable of fine-tuning loading and unloading of CD1d molecules. These results have important implications in understanding how to optimize lipid-loading onto antigen-presenting cells, to better harness iNKT cells central role at the interface between innate and adaptive immunity.

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Acknowledgments

We thank Prof. Alain R. Townsend (University of Oxford) for the gift of 293T cells secreting biotin-tagged human CD1d molecules. This work was supported by The Wellcome Trust Grants 084923/B/08/Z (to G.S.B.) and 084923Z/08/Z (to V.C.), Cancer Research UK Programme Grant C399/A2291 (to V.C.), Advanced Immunization Technologies Grant 280873 (to V.C.), and The Medical Research Council. G.S.B. acknowledges support in the form of a Personal Research Chair from Mr. James Bardrick.

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Information & Authors

Information

Published in

Go to Proceedings of the National Academy of Sciences
Proceedings of the National Academy of Sciences
Vol. 110 | No. 49
December 3, 2013
PubMed: 24248359

Classifications

Submission history

Published online: November 18, 2013
Published in issue: December 3, 2013

Keywords

  1. autoreactivity
  2. inflammation
  3. innate immunity
  4. lipid binding proteins

Acknowledgments

We thank Prof. Alain R. Townsend (University of Oxford) for the gift of 293T cells secreting biotin-tagged human CD1d molecules. This work was supported by The Wellcome Trust Grants 084923/B/08/Z (to G.S.B.) and 084923Z/08/Z (to V.C.), Cancer Research UK Programme Grant C399/A2291 (to V.C.), Advanced Immunization Technologies Grant 280873 (to V.C.), and The Medical Research Council. G.S.B. acknowledges support in the form of a Personal Research Chair from Mr. James Bardrick.

Notes

This article is a PNAS Direct Submission. M.K. is a guest editor invited by the Editorial Board.

Authors

Affiliations

Mariolina Salio2,1 [email protected]
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Headington, Oxford OX3 9DS, United Kingdom;
Hemza Ghadbane1
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Headington, Oxford OX3 9DS, United Kingdom;
Omer Dushek
Sir William Dunn School of Pathology, Oxford OX1 3RE, United Kingdom;
Dawn Shepherd
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Headington, Oxford OX3 9DS, United Kingdom;
Jeremy Cypen
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Headington, Oxford OX3 9DS, United Kingdom;
Uzi Gileadi
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Headington, Oxford OX3 9DS, United Kingdom;
Michael C. Aichinger
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Headington, Oxford OX3 9DS, United Kingdom;
Giorgio Napolitani
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Headington, Oxford OX3 9DS, United Kingdom;
Xiaoyang Qi
Division and Program in Human Genetics, Cincinnati Children’s Hospital Research Foundation, Cincinnati, OH 45229-3039;
P. Anton van der Merwe
Sir William Dunn School of Pathology, Oxford OX1 3RE, United Kingdom;
Justyna Wojno
School of Chemistry, and
School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom;
Natacha Veerapen
School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom;
Liam R. Cox
School of Chemistry, and
Gurdyal S. Besra
School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom;
Weiming Yuan
Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033; and
Peter Cresswell
Department of Immunobiology, Yale University School of Medicine, New Haven, CT 06520-8011
Vincenzo Cerundolo
Medical Research Council Human Immunology Unit, Radcliffe Department of Medicine, Medical Research Council Weatherall Institute of Molecular Medicine, University of Oxford, Headington, Oxford OX3 9DS, United Kingdom;

Notes

2
To whom correspondence should be addressed. E-mail: [email protected].
Author contributions: M.S., H.G., O.D., P.A.v.d.M., and V.C. designed research; M.S., H.G., D.S., and U.G. performed research; J.C., M.C.A., G.N., X.Q., J.W., N.V., L.R.C., G.S.B., W.Y., and P.C. contributed new reagents/analytic tools; M.S., H.G., O.D., P.A.v.d.M., and V.C. analyzed data; and M.S. and V.C. wrote the paper.
1
M.S. and H.G. contributed equally to this work.

Competing Interests

The authors declare no conflict of interest.

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    Saposins modulate human invariant Natural Killer T cells self-reactivity and facilitate lipid exchange with CD1d molecules during antigen presentation
    Proceedings of the National Academy of Sciences
    • Vol. 110
    • No. 49
    • pp. 19653-19969

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