The membrane protein of severe acute respiratory syndrome coronavirus acts as a dominant immunogen revealed by a clustering region of novel functionally and structurally defined cytotoxic T-lymphocyte epitopes.
BACKGROUND
Severe acute respiratory syndrome coronavirus (SARS-CoV), which emerged with highly contagious and life-threatening characteristics in 2002, remains a potential risk for future outbreaks. Membrane (M) and envelope (E) proteins are major structural proteins of the SARS-CoV. The M protein has been determined as a protective antigen in humoral responses. However, its potential roles in stimulating cellular immunity remain elusive.


METHODS
In this study, a panel of peptides derived from M and E proteins were tested by in vitro refolding, T2 cell-binding assays, and responses stimulated by cytotoxic T-lymphocyte (CTL) epitopes in HLA-A2.1/K(b) transgenic mice and human peripheral blood mononuclear cells (PBMCs).


RESULTS
A nonameric epitope Mn2 and a decameric epitope Md3 derived from the M protein were identified and used for the evaluation of M protein-specific immunity. Responses stimulated by M protein-specific CTL epitopes have been found in the PBMCs of donors who had recovered from SARS infection. Additionally, the transmembrane domain of the M protein may contain a T cell epitope cluster revealed by the immunogenic and structural analysis of a panel of truncated peptides overlapping with Mn2 and Md3.


CONCLUSIONS
The M protein of SARS-CoV holds dominant cellular immunogenicity. This, together with previous reports of a strong humoral response against the M protein, may help to further explain the immunogenicity of SARS and serves as potential targets for SARS-CoV vaccine design.
Liu
Jun
J
CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Graduate University, Beijing, China.
Sun
Yeping
Y
Qi
Jianxun
J
Chu
Fuliang
F
Wu
Hao
H
Gao
Feng
F
Li
Taisheng
T
Yan
Jinghua
J
Gao
George F
GF
D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D002352:Carrier Proteins; D000086862:Coronavirus M Proteins; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D015234:HLA-A Antigens / Q000378:metabolism; D015789:HLA-A2 Antigen; D006801:Humans; D007111:Immunity, Cellular; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D045473:Severe acute respiratory syndrome-related coronavirus / Q000276:immunology*; D045169:Severe Acute Respiratory Syndrome / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D019444:Vaccines, DNA / Q000276:immunology; D014763:Viral Matrix Proteins / Q000737:chemistry / Q000276:immunology*; D014765:Viral Vaccines / Q000276:immunology
D002352:Carrier Proteins; D000086862:Coronavirus M Proteins; D018984:Epitopes, T-Lymphocyte; D015234:HLA-A Antigens; C435939:HLA-A*02:01 antigen; D015789:HLA-A2 Antigen; C000706237:M protein, SARS-CoV; D019444:Vaccines, DNA; D014763:Viral Matrix Proteins; D014765:Viral Vaccines