Development of an indirect ELISA for the detection of serum IgG antibodies against region IV of phase 1 flagellin of Salmonella enterica serovar Brandenburg in sheep

Adjuvant-driven antibody response to use cows as biofactories of anti-SARS-CoV-2 neutralizing antibodies in colostrum

Cows produce a substantial amount of immunoglobulin in the colostrum, and nutraceutical products derived from these antibodies are gaining attention for their potential role in human viral disease prevention. The objective of our study was to develop an immunization schedule for pregnant cows to produce hyperimmune colostrum with antibodies presenting high avidity and neutralizing activity against SARS-CoV-2. The recombinant spike receptor-binding domain (RBD) from SARS-CoV-2, expressed using the Expi293F system and purified via Ni-affinity chromatography, was solubilized in (1) saponin (QuilA) or (2) a suspension of potassium and aluminum hydroxide (Alum). Vaccination of pregnant cows and serum sample collection were performed 45, 30, and 15 d before the expected calving date. Serum and colostrum were also collected on the day of parturition. Anti-RBD IgG, IgG1, and IgG2 production, viral neutralization, and antibody avidity were evaluated by ELISA. Cows immunized with recombinant RBD with the QuilA adjuvant produced higher amounts of all antibody subclasses than cows in the Alum group. The viral neutralization index from serum samples was also higher in the QuilA group. Significant differences were not observed in the avidity of antibodies, except for that of IgG2, which was higher in the serum of cows receiving the Alum formulation. As the IgG1 antibody subclass and its avidity are crucial for SARS-CoV-2 neutralization, QuilA might be the optimal adjuvant for producing hyperimmune colostrum in cows. These findings support the use of cows as biofactories of neutralizing antibodies against SARS-CoV-2 or any future emerging and re-emerging viral diseases, with the possibility of simply substituting the subunit antigen in the vaccine formulation. Further tests must be done to evaluate the efficacy of using hyperimmune colostrum as a nutraceutical or purified bovine antibodies as a pharmacological approach for COVID-19 prevention.

Abortion and various associated risk factors in dairy cow and sheep in Ili, China

We studied livestock abortion and various associated risk factors in the Ili region of northwest China. Livestock abortion prevalence was estimated and correlated with infections (Brucellosis, Salmonellosis, Mycoplasma and Chlamydia seropositivity) and management (farming type and contact with other herds/flocks) risk factors. A total of 2996 serum samples (1406 cow, 1590 sheep) were identified by RBPT (Rose Bengal Plate Test) and c-ELISA (competitive-enzyme linked immunosorbent assay), and they showed the overall seroprevalence of brucellosis in the study area was cow 6.76%, sheep 9.50%. The seroprevalence of brucellosis in X county was cow 7.06%, sheep 9.12%; in H county was cow 11.70%, sheep 10.80%; and in Q county was cow 4.22%, sheep 9.11%. The overall seroprevalence of Mycoplasma in the study area was cow 3.20%, sheep 6.42%. The seroprevalence of Mycoplasma in X county was cow 3.39%, sheep 7.98%; in H county was cow 5.26%, sheep 9.97%; and in Q county was cow 2.11%, sheep 4.33%. The Odds ratio of brucellosis for cow and sheep, respectively, were 45.909 [95% CI 26.912-78.317, P<0.001] and 70.507 [95% CI 43.783-113.544, P<0.001] times higher than other abortion-related factors including mixed farming, contact with other flocks and Mycoplasma infection. A total of 54 samples, including aborted cow (22), sheep (30) fetuses and milk samples (2), were identified as Brucella melitensis (B. melitensis) positive. A total of 38 Brucella were isolated from 16 aborted cow, 20 sheep fetuses and 2 milk samples. All of these isolates were identified, and confirmed, as B. melitensis. A phylogenetic tree showed that the Brucella isolates closely matched the B. melitensis biovar 3 isolated in Inner Mongolia, China, and B. melitensis isolated from Norway and India. These results suggest that B. melitensis biovar 3 is the main pathogen responsible for cow and sheep abortion and also pose a human health risk. Additionally, livestock reproduction can also be influenced by Mycoplasma infection and managerial factors (farming type and contact with other herds/flocks), especially in remote areas.

Application of Monoclonal Antibodies Developed Against the IpaJ Protein for Detection of Chickens Infected With Salmonella enterica Serovar Pullorum Using Competitive ELISA

Pullorum disease remains an epidemic in the poultry industry in China. The causing pathogen is a host-restricted Salmonella enterica serovar Pullorum, which can spread through both horizontal and vertical transmissions. To eradicate the pullorum disease from poultry farms, it is necessary to specifically monitor the prevalence of the bacterial infection in adult chicks. In this study, we constructed a new competitive ELISA method based on the development of monoclonal antibodies (MAbs) against a specific immunogen of S. Pullorum, IpaJ protein. In total, eight MAbs against IpaJ were prepared using the purified recombinant His-IpaJ protein as the immunogen. Characterization of the eight MAbs demonstrated that 4G5 can be used as the competitive antibody in ELISA. A competitive ELISA was subsequently developed using purified MBP-IpaJ as the capture (0.5 μg/ml) and the HRP-labeled 4G5 (0.14 μg/ml) as the competitive antibody, respectively. A specificity test demonstrated that the ELISA assay can differentiate antisera of S. Pullorum-infected chickens from that of S. Gallinarum and S. Enteritidis. Furthermore, 4 out of 200 clinical antisera collected from a poultry farm were detected to be S. Pulloram positive using this method. The plate agglutination test (PAT) and the previously established indirect ELISA confirmed that these positive antisera reacted specifically with S. Pullorum. We propose that the established competitive ELISA assay based on MAb against IpaJ protein, is a novel and quick method that can detect S. Pullroum infection in the poultry industry.

Purification of recombinant IpaJ to develop an indirect ELISA-based method for detecting Salmonella enterica serovar Pullorum infections in chickens

Background

Salmonella enterica serovar Pullorum is a host-restricted serotype causing infection in poultry. The pathogen can not only cause acute infection in young chicks with high mortality and morbidity, but also persist in adult chickens without evident clinical symptoms and lead to vertical transmission. To eradicate S. Pullorum in poultry farms, it is necessary to establish an efficient method to monitor the prevalence of the pathogen in adult chickens. The protein IpaJ is a specific immunogen in S. Pullorum and is not detected in closely related serotypes, such as S. Gallinarum and S. Enteritidis.

Results

In the present study, IpaJ was expressed as a recombinant fusion protein MBP-IpaJ in E. coli. The purified MBP-IpaJ was used as a coating antigen to develop an indirect ELISA assay, which was applied to the detection of S. Pullorum infection in chickens. The indirect ELISA assay demonstrated that antibodies produced against IpaJ were detectable in antisera of chickens infected with S. Pullorum in the second week, stably increased until the tenth week, and persisted at a high level in the following two weeks. Furthermore, the ELISA method detected four positive samples out of 200 clinical antiserum samples collected from a poultry farm, and the positive samples were confirmed to be reacted with S. Pullorum using the standard plate agglutination test.

Conclusions

The established indirect ELISA using the IpaJ protein is a novel method for specific detection of S. Pullorum infection, and contribute to eradication of pullorum disease in the poultry industry.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1753-0) contains supplementary material, which is available to authorized users.

A repertoire of high-affinity monoclonal antibodies specific to S. typhi: as potential candidate for improved typhoid diagnostic

Typhoid fever is a significant global health problem with highest burden on the developing world. The severity of typhoid is often underestimated, and currently available serological diagnostic assays are inadequate due to lack in requisite sensitivity and specificity. This underlines an absolute need to develop a reliable and accurate diagnostics that would benefit long-term disease control and treatment and to understand the real disease burden. Here, we have utilized flagellin protein of S. typhi that is surface accessible, abundantly expressed, and highly immunogenic, for developing immunodiagnostic tests. Flagellin monomers are composed of conserved amino-terminal and carboxy-terminal, and serovar-specific middle region. We have generated a panel of murine monoclonal antibodies (mAbs) against the middle region of flagellin, purified from large culture of S. typhi to ensure its native conformation. These mAbs showed unique specificity and very high affinity toward S. typhi flagellin without showing any cross-reactivity with other serovars. Genetic analysis of mAbs also revealed high frequency of somatic mutation due to antigenic selection process across variable region to achieve high binding affinity. These antibodies also displayed stable binding in stringent reaction conditions for antigen-antibody interactions, like DMSO, urea, KSCN, guanidinium HCl, and extremes of pH. One of the mAbs potentially reversed the TLR5-mediated immune response, in vitro by inhibiting TLR5-flagellin interaction. In our study, binding of these mAbs to flagellin, with high affinity, present on bacterial surface, as well as in soluble form, validates their potential use in developing improved diagnostics with significantly higher sensitivity and specificity.

Ultrasensitive rapid detection of human serum antibody biomarkers by biomarker-capturing viral nanofibers

Candida albicans (C. albicans) infection causes high mortality rates within cancer patients. Due to the low sensitivity of the current diagnosis systems, a new sensitive detection method is needed for its diagnosis. Toward this end, here we exploited the capability of genetically displaying two functional peptides, one responsible for recognizing the biomarker for the infection (antisecreted aspartyl proteinase 2 IgG antibody) in the sera of cancer patients and another for binding magnetic nanoparticles (MNPs), on a single filamentous fd phage, a human-safe bacteria-specific virus. The resultant phage is first decorated with MNPs and then captures the biomarker from the sera. The phage-bound biomarker is then magnetically enriched and biochemically detected. This method greatly increases the sensitivity and specificity of the biomarker detection. The average detection time for each serum sample is only about 6 h, much shorter than the clinically used gold standard method, which takes about 1 week. The detection limit of our nanobiotechnological method is approximately 1.1 pg/mL, about 2 orders of magnitude lower than that of the traditional antigen-based method, opening up a new avenue to virus-based disease diagnosis.