Mapping antigenic sites of an immunodominant surface lipoprotein of Mycoplasma agalactiae, AvgC, with the use of synthetic peptides

Mycoplasma agalactiae Vaccines: Current Status, Hurdles, and Opportunities Due to Advances in Pathogenicity Studies

Contagious agalactia (CA) is a serious multietiological disease whose classic etiological agent is Mycoplasma agalactiae and which causes high morbidity and mortality rates in infected herds. CA is classified as a notifiable disease by the World Organization for Animal Health due to its significant worldwide economic impact on livestock, primarily involving goat and sheep farms. The emergence of atypical symptoms and strains of M. agalactiae in wildlife ungulates reestablishes its highly plastic genome and is also of great epidemiological significance. Antimicrobial therapy is the main form of control, although several factors, such as intrinsic antibiotic resistance and the selection of resistant strains, must be considered. Available vaccines are few and mostly inefficient. The virulence and pathogenicity mechanisms of M. agalactiae mainly rely on surface molecules that have direct contact with the host. Because of this, they are essential for the development of vaccines. This review highlights the currently available vaccines and their limitations and the development of new vaccine possibilities, especially considering the challenge of antigenic variation and dynamic genome in this microorganism.

Multi-perspectives and challenges in identifying B-cell epitopes

The identification of B-cell epitopes (BCEs) in antigens is a crucial step in developing recombinant vaccines or immunotherapies for various diseases. Over the past four decades, numerous in silico methods have been developed for predicting BCEs. However, existing reviews have only covered specific aspects, such as the progress in predicting conformational or linear BCEs. Therefore, in this paper, we have undertaken a systematic approach to provide a comprehensive review covering all aspects associated with the identification of BCEs. First, we have covered the experimental techniques developed over the years for identifying linear and conformational epitopes, including the limitations and challenges associated with these techniques. Second, we have briefly described the historical perspectives and resources that maintain experimentally validated information on BCEs. Third, we have extensively reviewed the computational methods developed for predicting conformational BCEs from the structure of the antigen, as well as the methods for predicting conformational epitopes from the sequence. Fourth, we have systematically reviewed the in silico methods developed in the last four decades for predicting linear or continuous BCEs. Finally, we have discussed the overall challenge of identifying continuous or conformational BCEs. In this review, we only listed major computational resources; a complete list with the URL is available from the BCinfo website (https://webs.iiitd.edu.in/raghava/bcinfo/).

Assessment of the duration of maternal‐derived antibodies specific to the Mycoplasma agalactiae vaccine in goat kids

Background

Contagious agalactia (CA) is one of the most important diseases in the small ruminant industry in Iran. The historical aetiology of this disease is Mycoplasma agalactiae (Ma). The main way to control this disease, in addition to management measures, is vaccination. In ruminant newborns, determining the age of first vaccination against Ma is a challenge due to the interference between colostrum‐derived maternal immunity and vaccination‐induced immunity. The aim of this study was to evaluate the consistency of maternal‐derived antibodies specific to the Ma in goat kids blood serum born from the vaccinated does.

Objectives

Dtermination of level of antibody against Ma in goat kids born from vaccinated dams against Ma. Assessment of duration of protective level of maternal derived antibody in goat kids serum, after receiving colostrum from vaccinted mother with Ma vaccine. Determination the best time vaccination against Ma in goat kids receiving colostrum from vaccinated dams.

Methods

20 Saanen goat kids were studied in two groups of 10 animals including control (receiving colostrum from unvaccinated does) and treatment (receiving colostrum from vaccinated does). Indirect Elisa was used to evaluate serum specific antibodies to Ma in goat kids (control and treatment groups) from birth to 100 days of age.

Results

After receiving a sufficient amount of colostrum, the goat kids in the treatment group had a significantly higher S/P% than the control group until 56 days after birth (p < 0.05) and at 70–100 days after birth, there was no significant difference between the treatment and control groups (p > 0.05).

Conclusions

This study showed that 56–70 days of age could be a good age to give the first dose of CA vaccine in goat kids, but more studies are needed on the effectiveness of this vaccine at this age.

Identification of conserved Mycoplasma agalactiae surface antigens by immunoproteomics

Contagious agalactia represents one of the most relevant infectious diseases of dairy sheep, with Mycoplasma agalactiae being the primary etiological agent. The early, sensitive, and specific identification of infected animals, as well as the development of efficient prophylactic tools, remain challenging. Here, we present a comprehensive characterization of M. agalactiae antigens focusing on those shared among different isolates. Leveraging on previous proteomic data obtained on individual strains, we adopted a strategy entailing sample pooling to optimize the identification of conserved proteins that induce an immune response. The liposoluble proteins from previously characterized field isolates and the type strain PG2^T were enriched by Triton X-114 fractionation, pooled, analysed by one-dimensional (1D) and two-dimensional (2D) electrophoresis, and subjected to western immunoblotting against sheep sera collected during natural infection with M. agalactiae. Immunodominant antigens were identified by Matrix-Assisted Laser Desorption-Time-Of-Flight-Mass Spectrometry (MALDI-TOF-MS). This combined immunoproteomic approach confirmed the role of several known immunogens, including P80, P48, and P40, and most variable surface proteins (Vpmas), and unveiled novel immunodominant, conserved antigens, including MAG_1000, MAG_2220, MAG_1980, phnD, MAG_4740, and MAG_2430. Genomic context, functional prediction, subcellular localization, and invariable expression of these proteins in all isolates suggest their possible involvement in bacterial pathogenicity and metabolism. Moreover, most of the identified antigens elicit a host humoral response since the early stages of infection, persisting for at least 270 days. The immunodominant, conserved antigen panel identified in this work supports the development of effective vaccines and diagnostic tools with higher sensitivity and specificity in all the natural infection stages.

The Role of Lipoproteins in Mycoplasma-Mediated Immunomodulation

Mycoplasma infections, such as walking pneumonia or pelvic inflammatory diseases, are a major threat to public health. Despite their relatively small physical and genomic size, mycoplasmas are known to elicit strong host immune responses, generally inflammatory, while also being able to evade the immune system. The mycoplasma membrane is composed of approximately two-thirds protein and one-third lipid and contains several lipoproteins that are known to regulate host immune responses. Herein, the immunomodulatory effects of mycoplasma lipoproteins are reviewed. A better understanding of the immunomodulatory effects, both activating and evasive, of Mycoplasma surface lipoproteins will contribute to understanding mechanisms potentially relevant to mycoplasma disease vaccine development and treatment.

An Introduction to B-Cell Epitope Mapping and In Silico Epitope Prediction

Identification of B-cell epitopes is a fundamental step for development of epitope-based vaccines, therapeutic antibodies, and diagnostic tools. Epitope-based antibodies are currently the most promising class of biopharmaceuticals. In the last decade, in-depth in silico analysis and categorization of the experimentally identified epitopes stimulated development of algorithms for epitope prediction. Recently, various in silico tools are employed in attempts to predict B-cell epitopes based on sequence and/or structural data. The main objective of epitope identification is to replace an antigen in the immunization, antibody production, and serodiagnosis. The accurate identification of B-cell epitopes still presents major challenges for immunologists. Advances in B-cell epitope mapping and computational prediction have yielded molecular insights into the process of biorecognition and formation of antigen-antibody complex, which may help to localize B-cell epitopes more precisely. In this paper, we have comprehensively reviewed state-of-the-art experimental methods for B-cell epitope identification, existing databases for epitopes, and novel in silico resources and prediction tools available online. We have also elaborated new trends in the antibody-based epitope prediction. The aim of this review is to assist researchers in identification of B-cell epitopes.

Development of a specific immunomagnetic capture-PCR for rapid detection of viable Mycoplasma agalactiae in sheep milk samples

AIMS

To develop an immunomagnetic capture (IMC) to detect viable Mycoplasma agalactiae in routine ovine milk samples.

METHODS AND RESULTS

Polyclonal antibodies against two M. agalactiae membrane surface proteins (P80 and P55) were covalently conjugated to magnetic beads (MBs) to form MB-Ab80 and MB-Ab55. Mycoplasma agalactiae cells were captured by a specific antigen-antibody reaction and magnetic separation. Immunomagnetic capture (IMC) was used to isolate and concentrate M. agalactiae in serial decimal dilutions and in artificially contaminated milk to facilitate subsequent detection by PCR. A 375-bp fragment of M. agalactiae was amplified using a pair of M. agalactiae-specific primers in PCR. The limit of detection of IMC-PCR method ranged from 10 to 10(2)  CCU ml(-1) when mycoplasmas were resuspended in PBS and from 10(2) to 10(3)  CCU ml(-1) when mycoplasmas were resuspended in uncontaminated ovine milk. This study also describes the application of IMC-PCR method to test for M. agalactiae in 516 milk samples collected from sheep with suspected contagious agalactia. Its performance was evaluated relative to culture.

CONCLUSIONS

This report has demonstrated for the first time, the effective use of rapid and reliable IMC combined with PCR assay for the detection of viable M. agalactiae.

SIGNIFICANCE AND IMPACT OF THE STUDY

The method IMC-PCR provides an alternative to conventional microbiological detection, method and it could be applied to quick detection of M. agalactiae in routine sheep milk samples.

Synthesis of antimicrobial peptides using the SPOT technique

Developing new lead structures for drugs against multiresistant bacteria is an urgent need for modern medicine. Antimicrobial peptides are a class of drugs that can be used to discover such structures. In order to support development of this research, a fast, easy, and inexpensive method to synthesize peptides is necessary. The SPOT synthesis has the potential to produce the required peptide arrays, synthesizing up to 8,000 peptides, peptide mixtures, or other organic compounds on cellulose or other planar surfaces in a positionally addressable and multiple manner. Protocols for the preparation of cellulose membranes and the SPOT synthesis as well as cleavage of peptides from the support are described.

Vaccines for Mycoplasma diseases in animals and man

Vaccines for important mycoplasma diseases, including contagious bovine and caprine pleuropneumonia, have been used for centuries, consisting mainly of infected tissue or fluids which are inoculated into sites at which the risk of severe infection is slight, such as the tail and bridge of the nose. Surprisingly, little progress has been made in developing safe, defined and protective alternatives, the vaccines today still consisting of mildly attenuated strains serially passaged in eggs or in culture. Ill-defined temperature-sensitive mutants are widely used for mycoplasmoses in poultry despite uncertainty about their mode of protection. Inactivated vaccines for enzootic pneumonia appear to have improved pig health worldwide, but disease reduction has been generally modest. Ironically, attempts to develop subunit preparations have often led to exacerbation of disease, particularly in human atypical pneumonia. Promising results have been seen in DNA vaccine technology, which has been applied to the development of mycoplasma vaccines for porcine enzootic pneumonia, but field trials still seem a long way off. No commercial vaccines exist for Mycoplasma bovis, despite evidence that this is a major cause of calf pneumonia, mastitis and arthritis.

Genetic immunization with the immunodominant antigen P48 of Mycoplasma agalactiae stimulates a mixed adaptive immune response in BALBc mice

A DNA vaccine against contagious agalactia was developed for the first time, encoding the P48 of Mycoplasma agalactiae. Specific immune responses elicited in BALB/c mice were evaluated. Both total IgG and IgG1 were detected in mice vaccinated with pVAX1/P48. Proliferation of mononuclear cells of the spleen, levels of gamma interferon, interleukin-12, and interleukin-2 mRNAs were enhanced in immunized animals. Results indicate that pVAX1/P48 vaccination induced both T(h)1 and T(h)2 immune responses. Nucleic acid immunization could be a new strategy against M. agalactiae infections and may be potentially used to develop vaccines for other Mycoplasma diseases.

VNTR analysis reveals unexpected genetic diversity within Mycoplasma agalactiae, the main causative agent of contagious agalactia

BACKGROUND

Mycoplasma agalactiae is the main cause of contagious agalactia, a serious disease of sheep and goats, which has major clinical and economic impacts. Previous studies of M. agalactiae have shown it to be unusually homogeneous and there are currently no available epidemiological techniques which enable a high degree of strain differentiation.

RESULTS

We have developed variable number tandem repeat (VNTR) analysis using the sequenced genome of the M. agalactiae type strain PG2. The PG2 genome was found to be replete with tandem repeat sequences and 4 were chosen for further analysis. VNTR 5 was located within the hypothetical protein MAG6170 a predicted lipoprotein. VNTR 14 was intergenic between the hypothetical protein MAG3350 and the hypothetical protein MAG3340. VNTR 17 was intergenic between the hypothetical protein MAG4060 and the hypothetical protein MAG4070 and VNTR 19 spanned the 5' end of the pseudogene for a lipoprotein MAG4310 and the 3' end of the hypothetical lipoprotein MAG4320. We have investigated the genetic diversity of 88 M. agalactiae isolates of wide geographic origin using VNTR analysis and compared it with pulsed field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD) analysis. Simpson's index of diversity was calculated to be 0.324 for PFGE and 0.574 for VNTR analysis. VNTR analysis revealed unexpected diversity within M. agalactiae with 9 different VNTR types discovered. Some correlation was found between geographical origin and the VNTR type of the isolates.

CONCLUSION

VNTR analysis represents a useful, rapid first-line test for use in molecular epidemiological analysis of M. agalactiae for outbreak tracing and control.

The spot technique: synthesis and screening of peptide macroarrays on cellulose membranes

Peptide arrays are a widely used tool for drug development. For peptide-based drug design it is necessary to screen a large number of peptides. However, there are often difficulties with this approach. Most common peptide synthesis techniques are able to simultaneously synthesize only up to a few hundred single peptides. Spot synthesis is a positionally addressable, multiple synthesis technique offering the possibility of synthesizing and screening up to 10,000 peptides or peptide mixtures on cellulose or other membrane surfaces. In this chapter we present the basic procedures and screening methods related to spot synthesis and outline protocols for easy-to-use detection methods on these peptide arrays.

Development of a sensitive and specific enzyme-linked immunosorbent assay based on recombinant antigens for rapid detection of antibodies against Mycoplasma agalactiae in sheep

We developed a new recombinant enzyme-linked immunosorbent assay (rELISA) for serodiagnosis of contagious agalactia (CA), a disease caused by Mycoplasma agalactiae in sheep and goats. The assay is based on two M. agalactiae surface proteins, namely, P80 and P55. Identification of these immunodominant and common antigens was accomplished by examining the antibody response elicited in sheep during experimental infection and comparing it to the protein expression profiles of 75 M. agalactiae field strains. Our rELISA was tested with 343 sera, collected from sheep with a laboratory-confirmed diagnosis of CA (n = 223) and from healthy animals (n = 120). All sera had previously been tested by Western blotting (WB) for reactivity against M. agalactiae. In addition, our rELISA was compared with a commercial routine ELISA based on inactivated antigens (CHEKiT). Among the 223 samples that were WB positive for M. agalactiae, 209 (93.7%) tested positive for rP80-P55 with our ELISA, whereas only 164 (73.8%) tested positive with the CHEKiT ELISA. Among the 120 samples tested that were WB negative for M. agalactiae, 96.7% were confirmed as negative with our rELISA, while only 75.8% were confirmed as negative with the CHEKiT ELISA. A comparison of the results with receiver operating characteristic curves indicated that the differences observed between our rELISA and the CHEKiT ELISA are statistically significant. The use of recombinant peptides instead of inactivated antigens could significantly improve the discrimination of positive and negative animals, bringing significant advantages in controlling the import/export of live animals and helping in eradication of this economically detrimental disease.

Peptide arrays for the determination of humoral responses induced by active immunization with a monoclonal antibody against EpCAM

Epithelial cell adhesion molecule (EpCAM) is an attractive target for monoclonal antibody serotherapy because it is over-expressed in approximately 70% of epithelial cancers and their metastatic lesions. IGN101, the immunogenic formulation of the murine monoclonal anti-EpCAM antibody Mab17-1A, has been shown to evoke a strong humoral immune response in both monkey studies and early clinical trials. Notably, there was a reduction in the number of circulating EpCAM-positive tumor cells in the peripheral blood of treated cancer patients. In contrast to earlier publications by other groups, we could not detect an anti-EpCAM immune response upon treatment with Mab17-1A using a conventional but optimized anti-EpCAM ELISA. Therefore, in a novel experimental setup, sera of healthy immunized monkeys, normal human donors and cancer patients immunized with IGN101 were tested for reactivity against a series of overlapping synthetic peptides encompassing the entire sequence of EpCAM prepared by SPOT synthesis on cellular supports. Using this method, sera from normal donors reacted with different peptides compared to sera from healthy monkeys. However, the peptides were clustered in the same regions of EpCAM. Cancer patients generally had a lower reactivity to EpCAM peptides and immunization with IGN101 induced reactivity against a different set of peptides. Antibodies cross-reacting with both the IgG2a framework and with the Mab17-1A idiotype were identified. In summary, our data indicate that some EpCAM peptides may be recognized in a species-specific manner. At least seven EpCAM-derived peptides could be of diagnostic interest (QCQCTSVGAQ, ERVRTYWIII, ALQKEITTRY, TYWIIIELKH, IADVAYYFEK, AYYFEKDVKG, GQTLIYYVDE), while four out of these seven peptides may also possess therapeutic relevance (TYWIIIELKH, ALQKEITTRY, IADVAYYFEK, AYYFEKDVKG).

Characterisation of protein and antigen variability among Mycoplasma mycoides subsp. mycoides (LC) and Mycoplasma agalactiae field strains by SDS-PAGE and immunoblotting

Mycoplasma mycoides subsp. mycoides (LC) (Mmm LC) and Mycoplasma agalactiae are the most important mycoplasma species involved in the contagious agalactia syndrome. A total of 25 field strains from Spain and the two type strains were analysed by SDS-PAGE and immunoblotting. Two polyclonal antisera (PAbs) raised against a pool of strains of each mycoplasma species were used. The results revealed a high degree of protein variability among the field strains. The type strain of Mmm LC appeared to be representative of the field strains of this species, whereas this was not the case with the M. agalactiae type strain. Whereas M. agalactiae is known to possess a gene family regulating surface antigen diversity, there is a need to study the mechanisms used byMmm LC to generate antigenic variability in more detail.

Comparison of four diagnostic tests for the identification of serum antibodies in small ruminants infected withMycoplasma agalactiae

AIM

To determine the diagnostic capability of a newly developed Western blot (WB) assay for the detection of serum antibodies against Mycoplasma agalactiae compared with conventional serological tests, and to identify the best test for routine diagnostic use.

METHODS

The serological test methods used were: two commercial indirect enzyme-linked immunosorbent assays (ELISA), viz ELISA-1, using a bacterial antigen preparation, and ELISA-2, using a recombinant protein (lipoprotein p48) antigen; the complement fixation test (CFT); and a newly developed WB assay, the latter both using a bacterial antigen preparation. Thirty sera from goats infected with M. agalactiae and 97 sera from non-infected sheep were tested using all four methods.

RESULTS

Staining patterns in the WB were quite variable. An immuno-dominant band of 41 kDa was detected in 63% of sera from infected animals. The same band also appeared, although mostly very weakly, in 10% of sera from non-infected animals. When suspicious or very weak reactors were omitted, the diagnostic sensitivity (DSE) and diagnostic specificity (DSP), respectively, for the four assays were: WB=56.7%, 97.9%; ELISA-1=76.7%, 99.0%; ELISA-2=56.7%, 100%; and CFT=40.0%, 94.8%.

CONCLUSIONS

ELISA-1 performed best in this comparison. While the WB can be used, it did not have a technical advantage over the ELISA. The CFT should be discouraged as the primary screening method for contagious agalactia and should be replaced by ELISA-1. Results from this study confirm that serological test methods for contagious agalactia are useful for the detection of infected flocks but will not detect every individual infected animal.

Evaluation of a sensitive detection method for peptide arrays prepared by SPOT synthesis

The growing range of applications for peptide arrays prepared by SPOT synthesis confirms that they are a powerful proteomics technique to study numerous aspects of molecular interaction events. The most frequent application for peptide arrays prepared by SPOT synthesis is the identification of linear epitopes that are recognized by antibodies. In the conventional format using secondary antibodies for detection unspecific binding and high background have been observed. This leads to difficulties in evaluation of developed membranes. Especially for application with combinatorial libraries false positive results are to be avoided. To circumvent this issue, we directly labeled compounds of interest with biotin and detected binding by incubation with streptavidin-horseradish peroxidase via chemiluminescence. Optimization of method conditions led to a very sensitive detection technique with no or low number of unspecific spots, which is superior to conventional detection with secondary antibodies. As one consequence, evaluation of competitive assays got more reliable.

Profiling the immune responses of human patients treated with recombinant streptokinase after myocardial infarct

The SPOT synthesis of peptide arrays on continuous cellulose membranes should be generally applicable in the analysis of sequential antibody binding sites using the enzyme-substrate or other standard detection protocols. The use of total serum is limited by the occurrence of high background levels. This may be overcome if affinity purified antibodies or sera with high antibody titers are used, which allows work at high dilutions and a consequent reduction of background level. Here we demonstrate the mapping of antigenic regions located on recombinant streptokinase SK-2 (Heberkinase) using cellulose-bound peptide scans and human total sera from patients treated with SK-2 (Heberkinase). Streptokinase (SK) is a 47 kDa protein produced by various strains of hemolytic streptococci and is a potent activator of the fibrinolytic enzyme system in humans. SK is in widespread clinical use to treat acute infarction because of its function as an activator of vascular fibrinolysis. Since streptococcal infections are common, normal individuals are immunized with SK and antibodies (Abs) to SK can be detected in most of them. This therapy generates significant T-cell responses to SK and the neutralizing capacity of the Abs rises significantly. Neutralizing Abs reduces the efficiency of thrombolytic therapy and may cause allergic reactions. The widespread use of SK in humans makes its antigenicity an important clinical problem. In this regard the study of the immunodominant regions of SK becomes an important aspect for the improvement of this thrombolytic agent.

A dominant linear B-cell epitope of ricin A-chain is the target of a neutralizing antibody response in Hodgkin's lymphoma patients treated with an anti-CD25 immunotoxin

Hodgkin's lymphoma patients treated with an anti-CD25 Ricin toxin A-chain (RTA)-based Immunotoxin (RFT5.dgA) develop an immune response against the toxic moiety of the immunoconjugate. The anti-RTA antibody response of 15 patients showing different clinical features and receiving different total amounts of RFT5.dgA was therefore studied in detail, considering antibody titre, IgG and IgM content, average binding efficacy and ability to inhibit in vitro the cytotoxicity of a RTA-based Immunotoxin. No correlations were found between these parameters and the clinical features of the patients or the total amount of Immunotoxin administered. However, using a peptide scan approach we have identified a continuous epitope recognized by all patients studied, located within the stretch L161-I175 of the RTA primary sequence, close to a previously identified T-cell epitope. The ability of anti-L161-I175 antibodies to recognize folded RTA and to affect the biological activity of RTA by inhibiting RTA-IT cytotoxicity in vitro revealed that they may exert an important role in IT neutralization in vivo. Discovery of RTA immunodominant epitopes which are the target of anti-RTA immune response may lead to the development of immunomodulating strategies and to more successful treatment schedules.

Characterization of sodium dodecylsulfate polyacrylamide gel electrophoresis-separated M. agalactiae membrane antigens by mass spectrometry

Mycoplasma membrane proteins are generally designated according to their apparent molecular weight measured by SDS-PAGE. Several results about mycoplasma membrane antigens are conflicting because some doubts are emerging about the accuracy of the method utilised to identify the antigens. Aim of this work, was to characterise proteins separated after sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE)-mass spectrometry to allow an uncontroversial designation of the antigens. Fifteen proteins with molecular weights ranging from 15,000 to 80,000 Da had been excised from gel and their whole molecular weight and proteolytic pattern had been determined using MALDI-TOF. The peptide pattern obtained using trypsin digestion allowed us to identify LipA, P48, P59, P80 and P40. Some other proteins showed analogies to proteins of Mycoplasma genitalium or Mycoplasma pneumoniae the only Mycoplasmas completely sequenced. There wasn't a close correspondence between the SDS-PAGE apparent molecular weight (generally used to name the proteins), the gene derived calculated mass and the molecular weight of whole proteins measured by MALDI-TOF. Only micro sequence data obtained by MS/MS allowed us to identify LipC, described as one of the most important Mycoplasma agalactiae antigens. This protein was found in correspondence with the 50 kDa region, instead of the 25 kDa region, confirming a phenomenon that we previously described.