Overlapping Peptide Library to Map Qa-1 Epitopes in a Protein
Summary
Qa-1 (HLA-E in human) belongs to a group of non-classical major histocompatibility complex 1b molecules. Immunization with Qa-1-binding epitopes has been shown to augment tissue-specific immune regulation and ameliorate several autoimmune diseases. Herein we describe an overlapping peptide library strategy for the identification of Qa-1 epitopes in a protein.
Abstract
Qa-1 (HLA-E in human) belongs to a group of non-classical major histocompatibility complex 1b (MHC-Ib) molecules. Recent data suggest that Qa-1 molecules play important roles in surveying cells for structural and functional integrity, inducing immune regulation, and limiting immune responses to viral infections. Additionally, functional augmentation of Qa-1-restricted CD8+ T cells through epitope immunization has shown therapeutic effects in several autoimmune disease animal models, e.g. experimental allergic encephalomyelitis, collagen-induced arthritis, and non-obese diabetes. Therefore, there is an urgent need for a method that can efficiently and quickly identify functional Qa-1 epitopes in a protein. Here, we describe a protocol that utilizes Qa-1-restricted CD8+ T cell lines specific for an overlapping peptide (OLP) library for determining Qa-1 epitopes in a protein. This OLP library contains 15-mer overlapping peptides that cover the whole length of a protein, and adjacent peptides overlap by 11 amino acids. Using this protocol, we recently identified a 9-mer Qa-1 epitope in myelin oligodendrocyte glycoprotein (MOG). This newly mapped MOG Qa-1 epitope was shown to induce epitope-specific, Qa-1-restricted CD8+ T cells that enhanced myelin-specific immune regulation. Therefore, this protocol is useful for future investigation of novel targets and functions of Qa-1-restricted CD8+ T cells.
Introduction
Qa-1 belongs to a group of non-classical major histocompatibility complex 1b (MHC-Ib) molecules in mice. Its human homolog is HLA-E. Previous evidence has demonstrated that Qa-1 molecules have important biological functions. Firstly, Qa-1 molecules play an important role in surveying cells for structural and functional integrity. In this regard, Qa-1 molecules have evolved several strategies to monitor the normal function of a cell. One such strategy enables Qa-1 molecules to form complexes with a processed leader peptide (epitope), i.e. the Qa-1 determinant modifier (Qdm) that is processed from classical MHC-Ia molecules in the endoplasmic reticulum1. These Qa-1/Qdm complexes later display on the surface of a cell and bind to inhibitory NKG2A receptors on NK cells to inhibit NK killing activity2. If the expression of MHC-Ia molecules is lost, a cell (e.g. a malignant cell) becomes sensitive to NK killing2. The other strategy enables Qa-1 molecules to form new Qa-1/epitope complexes on the surface of a cell that is deficient in TAP (transporter associated with antigen processing)3 and/or ERAAP (endoplasmic reticulum aminopeptidase associated with antigen processing)4 (both deficiencies often occur in malignant cells). The cell that expresses these new Qa-1/epitope complexes can then be recognized and eliminated by the epitope-specific Qa-1-restricted CD8+ T cells. Secondly, Qa-1 molecules induce immune regulation5. In this regard, Qa-1/epitope complexes have been shown to stimulate CD8+ regulatory T (Treg) cells that are important for the prevention of immune-mediated damage of self-tissues6,7,8,9,10. Thirdly, Qa-1-restricted CD8+ Treg cells have been shown to limit immune responses against viral infection11.
Therefore, specific augmentation of epitope-specific Qa-1-restrictred CD8+ T cells is a potentially promising strategy for the elimination of abnormal cells, for the enhancement of immune regulation, and for the control of the magnitude of virus-induced immune responses. While it has not been determined whether augmentation of epitope-specific Qa-1-restricted CD8+ T cells can enhance immune surveillance and limit virus-induced immune responses, our laboratories and others have clearly demonstrated that immunization with Qa-1 epitopes can augment the function of Qa-1-restricted CD8+ Treg cells specific for pathogenic autoimmune CD4+ T cells, leading to efficient control of CD4+ T cell-mediated autoimmune diseases in a variety of animal models such as experimental allergic encephalomyelitis (an animal model of human multiple sclerosis)6,10, collagen-induced arthritis (an animal model of human rheumatoid arthritis)7, and non-obese diabetes (an animal model of human type 1 diabetes)8. Additionally, we have discovered that immunization with a tissue-specific Qa-1 epitope leads to specific control of immune-mediated inflammation in that tissue through augmentation of CD8+ Treg cells12. The above successes of preclinical studies indicate a need for a full evaluation of Qa-1 epitope immunization for the treatment of tissue-specific immune-mediated diseases and potentially for the therapy of other diseases associated with deficiencies in TAP and ERAAP.
Accordingly, there is a demand for a technology that can reliably and quickly analyze Qa-1 epitopes in a protein. In this regard, a limited number of biologically important Qa-1 epitopes has been described. Most of these Qa-1 epitopes were identified serendipitously during the study of CD8+ T cell responses to bacteria13, cells deficient in TAP3, cells deficient in ERAAP4, and cells that cause EAE6,9. Therefore, a high throughput technique is desirable for the identification of biologically important Qa-1 epitopes in a defined protein. In the following, we describe an overlapping peptide (OLP) library strategy that maps functional Qa-1 epitopes in a protein using Qa-1-resrticted CD8+ T cell lines specific for the OLP pool (OLP_pool) of a protein.
Protocol
Representative Results
Discussion
Here, we have described a protocol for analyzing Qa-1 epitopes in a protein. In relation to this protocol, several other strategies were also reported previously. First, allogeneic CD8+ T cell lines and clones were used for the identification of the Qdm1. Second, a putative Qa-1-binding motif from the analysis of Qdm was used for the identification of the HSP60p216-224 and a TCRBV8.1 epitope9,18. Third, individual overlapping pe…
Divulgaciones
The authors have nothing to disclose.
Acknowledgements
We thank Penelope Garcia for her technical assistance and preparation of this manuscript. This work was supported by a Research Innovation Grant (RIG) from the Department of Medicine at Loma Linda University (681205-2967) and a pilot grant from National Multiple Sclerosis Society (PP1685) to XT.
Materials
| The protein to be analyzed | N/A | N/A | Sequence of the protein can be obtained from NCBI |
| Dimethyl sulfoxide (DMSO) | Sigma-Aldrich | Cat#: D2650 SIGMA | DMSO should be sterile and cell culture tested. |
| Kb-/-Db-/- mice | The Lackson Laboratory | Stock#: 019995 | We used Taconic H2-KbH2-Db doube knockout mice (Cat#: 4215-F and 4215-M) which however are not available anymore. |
| AIM V Serum Free Medium | ThermoFisher Scientific | Cat#: 12055091 | |
| 2-mercaptoethanol | ThermoFisher Scientific | Cat#: 21985023 | |
| Sodium pyruvate | ThermoFisher Scientific | Cat#: 11360070 | |
| Nonessential Amino Acids | ThermoFisher Scientific | Cat#: 11140076 | |
| Dynabeads CD8 Positive Isolation Kit | ThermoFisher Scientific | Cat#: 11333D | |
| Bio-Gel P-100 | Bio-Rad | Cat#: 150-4171 | |
| Phoshate Balanced Solution (PBS) | ThermoFisher Scientific | Cat#: 20012027 | |
| Trasfer pipette | Globe Scientific | Mfg#: 137238 | |
| Murine M-CSF | PeproTech | Cat#: 315-02 | |
| 48-well tissue culture plates | USA Scientific | Cat#: CC7682-7548 | |
| Corning Costar TC-treated Multiple well Plates, 96-well, V-shaped bottom | Sigma-Aldrich | Cat#: Z372129 Sigma | |
| 1ml deep 06-well PP plate, sterile | USA Scientific | Item#: 1896-1110 | |
| Recombinant murine IL-2 | PeproTech | Cat#: 212-12 | |
| Recombinant murine IL-7 | PeproTech | Cat#L: 217-17 | |
| Capture anti-IFN-γ antibody | BD Biosciences | Cat#: 551881 | |
| ELISPOT plate | Sigma-Aldrich | Cat#: S2EM004M99 | |
| C1R | ATCC | Cat#: ATCC CRL-1993 | |
| C1R.Qa-1b | Custom made (GenBank access#: NM_010398.3) | ||
| Qa-1 lentiviral vector | GeneCopoeia | Product#: Mm02955 | |
| Detection anti-IFN-γ antibody | BD Biosciences | Cat#: 551881 | |
| Tween20 | Sigma-Aldrich | Cat#: P9416 | |
| Streptavidin-HRP | BD Biosciences | Cat#: BD557630 | |
| AEC substrate | BD Biosciences | Cat#: 551951 | |
| ImmunoSpot Analyzer | ImmunoSpot | Any immunoSpot analyer should work for this purpose. |
Referencias
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