Identification and characterization of novel B-cell epitopes within EBV latent membrane protein 2 (LMP2)

A Promising Tool in Serological Diagnosis: Current Research Progress of Antigenic Epitopes in Infectious Diseases

Infectious diseases, caused by various pathogens in the clinic, threaten the safety of human life, are harmful to physical and mental health, and also increase economic burdens on society. Infections are a complex mechanism of interaction between pathogenic microorganisms and their host. Identification of the causative agent of the infection is vital for the diagnosis and treatment of diseases. Etiological laboratory diagnostic tests are therefore essential to identify pathogens. However, due to its rapidity and automation, the serological diagnostic test is among the methods of great significance for the diagnosis of infections with the basis of detecting antigens or antibodies in body fluids clinically. Epitopes, as a special chemical group that determines the specificity of antigens and the basic unit of inducing immune responses, play an important role in the study of immune responses. Identifying the epitopes of a pathogen may contribute to the development of a vaccine to prevent disease, the diagnosis of the corresponding disease, and the determination of different stages of the disease. Moreover, both the preparation of neutralizing antibodies based on useful epitopes and the assembly of several associated epitopes can be used in the treatment of disease. Epitopes can be divided into B cell epitopes and T cell epitopes; B cell epitopes stimulate the body to produce antibodies and are therefore commonly used as targets for the design of serological diagnostic experiments. Meanwhile, epitopes can fall into two possible categories: linear and conformational. This article reviews the role of B cell epitopes in the clinical diagnosis of infectious diseases.

Novel EBV LMP-2-affibody and affitoxin in molecular imaging and targeted therapy of nasopharyngeal carcinoma

Epstein-Barr virus (EBV) infection is closely linked to several human malignancies including endemic Burkitt’s lymphoma, Hodgkin’s lymphoma and nasopharyngeal carcinomas (NPC). Latent membrane protein 2 (LMP-2) of EBV plays a pivotal role in pathogenesis of EBV-related tumors and thus, is a potential target for diagnosis and targeted therapy of EBV LMP-2⁺ malignant cancers. Affibody molecules are developing as imaging probes and tumor-targeted delivery of small molecules. In this study, four EBV LMP-2-binding affibodies (Z_{EBV LMP-2}12, Z_{EBV LMP-2}132, Z_{EBV LMP-2}137, and Z_{EBV LMP-2}142) were identified by screening a phage-displayed LMP-2 peptide library for molecular imaging and targeted therapy in EBV xenograft mice model. Z_{EBV LMP-2} affibody has high binding affinity for EBV LMP-2 and accumulates in mouse tumor derived from EBV LMP-2⁺ xenografts for 24 h after intravenous (IV) injection. Subsequent fusion of Pseudomonas exotoxin PE38KDEL to the Z_{EBV LMP-2} 142 affibody led to production of Z142X affitoxin. This fused Z142X affitoxin exhibits high cytotoxicity specific for EBV⁺ cells in vitro and significant antitumor effect in mice bearing EBV⁺ tumor xenografts by IV injection. The data provide the proof of principle that EBV LMP-2-speicifc affibody molecules are useful for molecular imaging diagnosis and have potentials for targeted therapy of LMP-2-expressing EBV malignancies.

Molecular imaging diagnosis and targeted therapy have been successfully used for several types of tumors, but not yet applied to diagnose or treat EBV-associated NPC. Affibody molecules are small proteins engineered to bind to a large number of target proteins with high affinity, and therefore, can be developed as potential biopharmaceutical drugs for molecular diagnosis and therapeutic applications. In the present study, we screened and characterized EBV LMP-2-specific affibodies and evaluated their usage in molecular imaging of LMP-2 expressing cells and EBV LMP-2 tumor-bearing mice. Subsequently, we engineered and obtained an EBV LMP-2 affitoxin based on EBV LMP-2-binding affibodies and demonstrated its targeted cytotoxicity for EBV⁺ cell lines in vitro and in vivo. Our data indicate that the EBV LMP-2-specific affibody and its derived affitoxin are useful for diagnosis of LMP-2 expressing cells and targeted therapy of EBV-derived, LMP-2⁺ malignancies.

Novel ELISA for serodiagnosis of nasopharyngeal carcinoma based on a B cell epitope of Epstein-Barr virus latent membrane protein 2

Epstein-Barr virus (EBV) is widespread and is associated with nasopharyngeal carcinoma (NPC). Serological detection of EBV is commonly used for screening, diagnosis and epidemiological surveys of NPC. In the present study, a novel B cell multi-epitope peptide fusion protein (EBV-LMP2-3B), which is composed of three B cell linear epitopes (RIEDPPFNSLL, TLNLT and KSLSSTEFIPN) of EBV latent membrane protein 2 (LMP2), was expressed in a prokaryotic expression system and purified using Ni²⁺-nitrilotriacetate-Sepharose. The immunogenicity and binding specificity of EBV-LMP2-3B were evaluated on the basis of antibody responses in immunized BALB/c mice, western blotting and indirect immunofluorescence assay. Evaluation of EBV-LMP2-3B as a serological diagnostic reagent was performed using an indirect ELISA in 198 patients with NPC and 102 healthy adults. These results revealed that EBV-LMP2-3B was able to eliminate the high-titer serum antibody response in BALB/c mice. Western blot analysis and indirect immunofluorescence assay confirmed that the mouse immune sera recognized the native LMP2. Compared with healthy adults, patients with NPC demonstrated significantly greater reactivity to EBV-LMP2-3B (P<0.05). Furthermore, it was possible to effectively detect specific IgG in sera from patients with NPC, with a sensitivity of 91.91% and specificity of 93.14%, representing an improvement over the traditional viral capsid antigen-IgA-based detection method with 59.59% sensitivity and 75.49% specificity. In conclusion, the EBV-LMP2-3B protein may be used as a serological diagnostic reagent to screen for and diagnose NPC.

The Possible Effect of B-Cell Epitopes of Epstein-Barr Virus Early Antigen, Membrane Antigen, Latent Membrane Protein-1, and -2A on Systemic Lupus Erythematosus

This study was aimed to evaluate the role of B-cell epitopes of Epstein-Barr virus (EBV) Early antigen protein D (EA), envelope glycoprotein GP340/membrane antigen (MA), latent membrane protein (LMP)-1, and LMP-2A in systemic lupus erythematosus (SLE). B-cell epitopes were predicted by analyzing secondary structure, transmembrane domains, surface properties, and homological comparison. 60 female mice were randomized equally into 12 groups: 1-10 groups were immunized by epitope peptides (EPs) 1-10, respectively, while 11 and 12 groups were PBS and Keyhole limpet hemocyanin (KLH) control groups. Immunoglobulin G (IgG) and autoantibody to nuclear antigen (ANA) concentrations in mice serum were determined at week 8. Indirect levels of EP1-10 were further detected by enzyme-linked immuno sorbent assay (ELISA) in 119 SLE patients and 64 age- and gender-matched health controls (HCs). 10 probable EBV EA, MA, LMP-1, and LMP-2A B-cell epitopes related to SLE self-antigens were predicted and corresponding EP1-10 were synthesized. IgG concentrations at week 8 were increased in EP1-10 and KLH groups compared with PBS group in mice; while ANA levels were elevated in only EP1-4, EP6-7, and EP10 groups compared to KLH group by ELISA, and ANA-positive rates were increased in only EP1, EP2, EP4, EP6, and EP10 groups by indirect immunofluorescence assay. EP1-4, EP6, and EP10 indirect levels were increased in SLE patients than HCs, while EP1, EP3, EP6, and EP9 were correlated with SLE disease activity index score. In conclusion, EBV EA, MA, LMP-1, and LMP-2A B-cell EPs increased SLE-related autoantibodies in mice, and their indirect levels might be served as potential biomarkers for SLE diagnosis and disease severity.

Chimerically fused antigen rich of overlapped epitopes from latent membrane protein 2 (LMP2) of Epstein-Barr virus as a potential vaccine and diagnostic agent

Epstein-Barr virus (EBV) is prevalent throughout the world and is associated with several malignant diseases in humans. Latent membrane protein 2 (LMP2) of EBV plays a crucial role in the pathogenesis of EBV-associated tumors; therefore, LMP2 has been considered to be a potential immunodiagnostic and immunotherapeutic target. A multi-epitope-based antigen is a promising option for therapeutic vaccines and diagnoses of such malignancies. In this study, we systematically screened cytotoxic T lymphocyte (CTL), helper T cell (Th) and B-cell epitopes within EBV-LMP2 using bioinformatics. Based on the screen, two peptides rich in overlapping epitopes of both T cells and B cells were selected to construct a plasmid containing the sequence for a chimeric multi-epitope protein referred to as EBV-LMP2m, which is composed of LMP2aa195∼232 and LMP2aa419∼436. The EBV-LMP2m protein was expressed in E. coli BL21 (DE3) after prokaryotic codon optimization. Inoculation of the purified chimeric antigen in BALB/c mice induced not only high levels of specific IgG in the serum and secretory IgA in the vaginal mucus but also a specific CTL response. By using purified EBV-LMP2m as an antigen, the presence of specific IgG in the serum specimens of 202 nasopharyngeal carcinoma (NPC) patients was effectively detected with 52.84% sensitivity and 95.40% specificity, which represents an improvement over the traditional detection method based on VCA-IgA (60.53% sensitivity and 76.86% specificity). The above results indicate that EBV-LMP2m may be used not only as a potential target antigen for EBV-associated tumors but also a diagnostic agent for NPC patients.