Synthetic-peptide-based enzyme-linked immunosorbent assay for screening human serum or plasma for antibodies to human immunodeficiency virus type 1 and type 2

The use of peptides for immunodiagnosis of human Chagas disease

Chagas disease, caused by the protozoa Trypanosoma cruzi, continues to be a serious public health problem in Latin America, worsened by the limitations in its detection. Given the importance of developing new diagnostic methods for this disease, the present review aimed to verify the number of publications dedicated to research on peptides that demonstrate their usefulness in serodiagnosis. To this end, a bibliographic survey was conducted on the PubMed platform using the keyword "peptide" or "epitope" combined with "Chagas disease" or "Trypanosoma cruzi"; "diagno*" or "serodiagnosis" or "immunodiagnosis", without period restriction. An increasing number of publications on studies employing peptides in ELISA and rapid tests assays was verified, which confirms the expansion of research in this field. It is possible to observe that many of the peptides tested so far originate from proteins widely used in the diagnosis of Chagas, and many of them are part of commercial tests developed. In this sense, as expected, promising results were obtained for several peptides when tested in ELISA, as many of them exhibited sensitivity and specificity values above 90%. Furthermore, some peptides have been tested in several studies, confirming their diagnostic potential. Despite the promising results observed, it is possible to emphasize the need for extensive testing of peptides, using different serological panels, in order to confirm their potential. The importance of producing an effective assay capable of detecting the clinical stages of the disease, as well as new immunogenic antigens that enable new serological diagnostic tools for Chagas disease, is evident.

Use of Phage Display technology in development of canine visceral leishmaniasis vaccine using synthetic peptide trapped in sphingomyelin/cholesterol liposomes

Background

Leishmania parasites can cause visceral or cutaneous disease and are found in subtropical and tropical regions of the Old and New World. The pathology of the infection is determined by both host immune factors and species/strain differences of the parasite. Dogs represent the major reservoir of Leishmania infantum (syn. L. chagasi) and vaccines are considered the most cost-effective control tools for canine disease.

Methods

Selection of immunodominant peptides was performed by Phage Display to identify sequences recognized by L. infantum naturally infected animals. Sera from Leishmania infected animals were used in the biopanning to selection of specific peptides. Serum samples from T. cruzi infected and healthy animals were used as control. After selection, synthetic peptides were produced in membrane (spot-synthesis) in soluble form and blotting and ELISA were performed for validation of serum reactivity. Selected peptide was formulated with aluminum hydroxide and liposomes and immunization was performed in BALB/c mice. Protection was determined by qPCR after challenge infection with virulent L. infantum.

Results

We reported the selection of Peptide 5 through Phage Display technique and demonstrate its ability to promote a state of immunity against L. infantum infection in murine model after immunization using liposomes as vaccine carrier. Our results demonstrate that immunization with Peptide 5 when formulated with aluminum hydroxide and liposomes is immunogenic and elicited significant protection associated with the induction of mixed Th1/Th2 immune response against L. infantum infection.

Conclusion

Peptide 5 is a promising vaccine candidate and the findings obtained in the present study encourage canine trials to confirm the effectiveness of a vaccine against CVL.

High-throughput analysis of synthetic peptides for the immunodiagnosis of canine visceral leishmaniasis

Background

Visceral leishmaniasis is the most severe form of leishmaniasis. Approximately 20% of zoonotic human visceral leishmaniasis worldwide is caused by Leishmania infantum, which is also known as Leishmania chagasi in Latin America, and disease incidence is increasing in urban and peri-urban areas of the tropics. In this form of disease, dogs are the main reservoirs. Diagnostic methods used to identify Leishmania infected animals are not able to detect all of the infected ones, which can compromise the effectiveness of disease control. Therefore, to contribute to the improvement of diagnostic methods for canine visceral leishmaniasis (CVL), we aimed to identify and test novel antigens using high-throughput analysis.

Methodology/Principal Findings

Immunodominant proteins from L. infantum were mapped in silico to predict B cell epitopes, and the 360 predicted peptides were synthesized on cellulose membranes. Immunoassays were used to select the most reactive peptides, which were then investigated with canine sera. Next, the 10 most reactive peptides were synthesized using solid phase peptide synthesis protocol and tested using ELISA. The sensitivity and specificity of these peptides were also compared to the EIE-LVC Bio-Manguinhos kit, which is recommended by the Brazilian Ministry of Health for use in leishmaniasis control programs. The sensitivity and specificity of the selected synthesized peptides was as high as 88.70% and 95.00%, respectively, whereas the EIE-LVC kit had a sensitivity of 13.08% and 100.00% of specificity. Although the tests based on synthetic peptides were able to diagnose up to 94.80% of asymptomatic dogs with leishmaniasis, the EIE-LVC kit failed to detect the disease in any of the infected asymptomatic dogs.

Conclusions/Significance

Our study shows that ELISA using synthetic peptides is a technique with great potential for diagnosing CVL; furthermore, the use of these peptides in other diagnostic methodologies, such as immunochromatographic tests, could be beneficial to CVL control programs.

Globally, the number of new human cases of visceral leishmaniasis (VL) is estimated to be approximately 500,000 per year. This is the most severe of all forms of leishmaniasis, and the zoonotic form of VL, caused by Leishmania infantum (also known as Leishmania chagasi), represents 20% of human visceral leishmaniasis worldwide; additionally, its prevalence is increasing in urban and peri-urban areas of the tropics. In Brazil, the identification and elimination of infected dogs, which act as a reservoir for Leishmania parasites, is a control measure employed in addition to the use of insecticides against the vectors and the identification and treatment of infected humans. Currently, the diagnostic methods employed to identify infected animals are not able to detect all of these dogs, which compromises the effectiveness of control measures. Moreover, one of the most important issues in controlling VL is the difficulty of diagnosing asymptomatic dogs, which act as parasite reservoirs. Therefore, to contribute to the improvement of the diagnostic methods for CVL, we aimed to identify and characterize new antigens that were more sensitive and specific and could be applied in epidemiologic surveys.

Surface plasmon resonance biosensor for direct detection of antibody against Epstein-Barr virus

This paper describes the direct label-free detection of antibodies against the Epstein-Barr virus (anti-EBNA) using a surface plasmon resonance (SPR) biosensor. The antibody detection was performed using the immunoreaction between anti-EBNA and a respective synthetic peptide (EBNA-1), which was conjugated with bovine serum albumin (BSA-EBNA) and immobilized on the sensor surface. Three immobilization chemistries for the attachment of BSA-EBNA were investigated to optimize ligand density and minimize loss of EBNA-1 immunoreactivity. The developed SPR biosensor functionalized with the optimal immobilization method was calibrated and characterized in terms of detection limit, reproducibility, regenerability and storability. It was demonstrated that the sensor is capable of detecting concentrations of anti-EBNA as low as 0.2 ng/ml (approximately 1 pM) both in buffer and 1% human serum and can be stored and regenerated for repeated use.

Evaluation and diagnostic usefulness of domestic and imported enzyme-linked immunosorbent assays for detection of human immunodeficiency virus type 1 antibody in India

Diagnosis of human immunodeficiency virus (HIV) infection is important for patient management and prevention of new infections. The number of test kits available for the detection of HIV antibodies is unprecedented. In order to identify appropriate test kits, we evaluated a variety of commercial kits manufactured abroad as well as in India. The plasma and serum specimens (n=264) were collected from individuals attending the Voluntary Counseling and Testing Centre at the YRG Centre for AIDS and Education. The specimens were used to evaluate six commercially available HIV test kits: Enzaids HIV 1+2, HIV-CheX, Murex HIV-1.2.0, Genscreen HIV 1/2 version 2, Vironostika HIV Uni-Form II Ag/Ab, and CombAids RS Advantage. High sensitivities and specificities (>or=99%) were observed for the Enzaids, Murex, Vironostika, and CombAids assays. HIV-CheX showed the highest number of false-positive and false-negative results. The Genscreen test also gave many false positives. The study indicated that the Enzaids, Murex, and Vironostika enzyme-linked immunosorbent assay kits and the CombAids RS Advantage rapid assay could be used to achieve acceptable results for the detection of HIV antibodies. A combination of two tests is recommended to optimize the efficiency of HIV antibody testing algorithms, especially when evaluation with an HIV Western blot confirmatory test is not possible.

Use of a new dual-antigen enzyme-linked immunosorbent assay to detect and characterize the human antibody response to the human immunodeficiency virus type 2 envelope gp125 and gp36 glycoproteins

A dual-antigen enzyme-linked immunosorbent assay specific for human immunodeficiency virus type 2 (HIV-2) envelope proteins, ELISA-HIV2, was developed with two new recombinant polypeptides, rpC2-C3 and rgp36, derived from the HIV-2 envelope. The diagnostic performance was determined with HIV-2, HIV-1, and HIV-1/2 samples. Both polypeptides showed 100% specificity. Clinical sensitivity was 100% for rgp36 and 93.4% for rpC2-C3. ELISA-HIV2 may be used for the specific diagnosis and confirmation of HIV-2 infection.

Assessment of synthetic peptides for hepatitis A diagnosis using biosensor technology

In the present work we demonstrate the application of a commercial biosensor instrument (BIACORE 1000, Biacore AB, Uppsala) for the detection of antibodies against the hepatitis A virus (HAV) in human serum samples using linear and branched synthetic peptides related to the VP3 capsid protein of HAV. We also studied the conformation of the synthetic peptides by circular dichroism (CD) in order to analyse the changes in secondary structure of the constructs that could influence their recognition by antibodies. Linear and dimeric VP3(110-121) multiple antigen peptides (MAP) were the most sensitive and appropriate for serological studies of serum from HAV infected patients using BIACORE. Immobilization of tetrameric MAPs via amine groups apparently failed to preserve the active conformation of the peptide epitope since it led to lower antibody binding compared to linear and dimeric peptides. The CD analysis showed that the tetrameric MAP constructs tend to adopt a beta-sheet structure due to intermolecular aggregation, which limits epitope accessibility. Our results demonstrate the value of biospecific interaction analysis technology using synthetic peptides for the diagnosis of acute hepatitis A.

Evaluation of antibodies against a rubella virus neutralizing domain for determination of immune status

The protective immune responses against rubella virus (RV) are related to its neutralizing epitopes, an issue that is important to consider when assessing the immune status of patients with remote infection. In the present paper, we compare the antibodies detected by a synthetic-peptide-based enzyme immunoassay (EIA) with antibodies detected by the traditional technique of hemagglutination inhibition (HIA) in patients with remote RV infection. The synthetic peptide used as an antigen (SP15) represents a neutralizing epitope that corresponds to amino acids 208 to 239 of the E1 glycoprotein. The SP15-EIA was developed, all variables that affected the assay were standardized, and the test was validated using reference sera. Serum samples (n = 129) from patients with remote RV infection were tested by HIA and SP15-EIA. Discrepant sera were assayed by MEIA (IMX/Abbot). The comparison between HIA and SP15-EIA, taking HIA as the standard methodology for determining immune status, showed that SP15-EIA is very specific and sensitive for detecting protecting antibodies (specificity, 100%; sensitivity, 98.20%). This study demonstrates that antibodies against the neutralizing domain represented by SP15 would be important in the memory response after natural infection and may be a good tool in the determination of the true immune status of patients with remote infection with regard to RV.

Use of linear and multiple antigenic peptides in the immunodiagnosis of acute hepatitis A virus infection

The reactivities of two panels of anti-HAV human sera from geographically distinct areas (Chile and Spain) to synthetic peptides from the VP1, VP2 and VP3 hepatitis A virus capsid proteins were examined by an enzyme-linked immunosorbent assay (ELISA) procedure. Two and four branched multiple antigenic peptides (MAPs) and palmitoylated peptides were compared with free synthetic sequences for the detection of IgM anti-HAV antibodies in the two panels of human sera. Our results showed that acute hepatitis A patient sera recognized preferentially homogeneous two branched MAPs and palmitic acid conjugated peptides. The palmitoyl-derived VP3(110-121) peptide and the corresponding dimeric MAP were the most sensitive and appropriate for serological studies of HAV-infected patients by ELISA, sensitivity and specificity being higher than 90% and 95%, respectively. These peptide-based tests open up new avenues in the development of peptide-based immunosorbent assays for the detection of acute HAV disease.