Intramuscular but not nebulized administration of a mRNA vaccine against Rhodococcus equi stimulated humoral immune responses in neonatal foals

OBJECTIVE

Design and evaluate immune responses of neonatal foals to a mRNA vaccine expressing the virulence-associated protein A (VapA) of Rhodococcus equi.

ANIMALS

Cultured primary equine respiratory tract cells; Serum, bronchoalveolar lavage fluid (BALF), and peripheral blood mononuclear cells (PBMCs) from 30 healthy Quarter Horse foals.

METHODS

VapA expression was evaluated by western immunoblot in cultured equine bronchial cells transfected with 4 mRNA constructs encoding VapA. The mRNA construct with greatest expression was used to immunize foals at ages 2 and 21 days in 5 groups: (1) 300 μg nebulized mRNA (n = 6); (2) 600 μg nebulized mRNA (n = 4); (3) 300 μg mRNA administered intramuscularly (IM) (n = 5); (4) 300 μg VapA IM (positive controls; n = 6); or (5) nebulized water (negative controls; n = 6). Serum, BALF, and PBMCs were collected at ages 3, 22, and 35 days and tested for relative anti-VapA IgG1, IgG4/7, and IgA activities using ELISA and cell-mediated immunity by ELISpot.

RESULTS

As formulated, nebulized mRNA was not immunogenic. However, a significant increase in anti-VapA IgG4/7 activity (P < .05) was noted exclusively in foals immunized IM with VapA mRNA by age 35 days. The proportion of foals with anti-VapA IgG1 activity > 30% of positive control differed significantly (P = .0441) between negative controls (50%; 3/6), IM mRNA foals (100%; 5/5), and IM VapA (100%; 6/6) groups. Natural exposure to virulent R equi was immunogenic in some negative control foals.

CLINICAL RELEVANCE

Further evaluation of the immunogenicity and efficacy of IM mRNA encoding VapA in foals is warranted.

Impact of surface receptors TLR2, CR3, and FcγRIII on Rhodococcus equi phagocytosis and intracellular survival in macrophages

The virulence-associated protein A (VapA) produced by virulent Rhodococcus equi allows it to replicate in macrophages and cause pneumonia in foals. It is unknown how VapA interacts with mammalian cell receptors, but intracellular replication of avirulent R. equi lacking vapA can be restored by supplementation with recombinant VapA (rVapA). Our objectives were to determine whether the absence of the surface receptors Toll-like receptor 2 (TLR2), complement receptor 3 (CR3), or Fc gamma receptor III (FcγRIII) impacts R. equi phagocytosis and intracellular replication in macrophages, and whether rVapA restoration of virulence in R. equi is dependent upon these receptors. Wild-type (WT) murine macrophages with TLR2, CR3, or FcγRIII blocked or knocked out (KO) were infected with virulent or avirulent R. equi, with or without rVapA supplementation. Quantitative bacterial culture and immunofluorescence imaging were performed. Phagocytosis of R. equi was not affected by blockade or KO of TLR2 or CR3. Intracellular replication of virulent R. equi was not affected by TLR2, CR3, or FcγRIII blockade or KO; however, avirulent R. equi replicated in TLR2-/- and CR3-/- macrophages but not in WT and FcγRIII-/-. rVapA supplementation did not affect avirulent R. equi phagocytosis but promoted intracellular replication in WT and all KO cells. By demonstrating that TLR2 and CR3 limit replication of avirulent but not virulent R. equi and that VapA-mediated virulence is independent of TLR2, CR3, or FcγRIII, our study provides novel insights into the role of these specific surface receptors in determining the entry and intracellular fate of R. equi.

Serum activities of complement 1q and antibodies to the virulence-associated protein A are lower in foals that develop rhodococcal pneumonia

OBJECTIVE

To determine the effects of transfusion of Rhodococcus equi hyperimmune plasma (REHIP) on serum concentrations of complement component 1q (C1q) and to examine the association of serum C1q and anti-rhodococcal antibodies of newborn foals with subsequent development of rhodococcal pneumonia.

ANIMALS/SAMPLES

Foals (n = 205) from 2 Thoroughbred breeding farms in New York transfused with REHIP between January 1, 2022, and December 1, 2022.

PROCEDURES

Blood was collected immediately before transfusion with REHIP and again from the contralateral vein immediately after transfusion. Foals were followed through weaning for clinical and ultrasonographic evidence of rhodococcal pneumonia. Serum samples were tested by ELISA for concentrations of C1q and for activity of IgG1 and IgG4/7 recognizing the virulence-associated protein A (VapA) of R equi. Logistic regression analysis was used to determine the association between rhodococcal pneumonia and levels of C1q and anti-VapA IgG1 and IgG4/7.

RESULTS

REHIP significantly decreased C1q concentrations immediately after transfusion. Accounting for effects of farm and birth month, estimated odds of pneumonia were 2.1-fold (P = .0330) higher for foals with pretransfusion C1q concentrations less than or equal to the population median and 3.3-fold (P = .0051) higher for foals with posttransfusion IgG1 activity in the lower quartile.

CLINICAL RELEVANCE

Both C1q and IgG appear to contribute to protection against R equi, and IgG1 appears to be especially important. Increasing IgG1 concentrations targeting rhodococcal proteins in REHIP or serum of foals might improve protection against R equi foal pneumonia.

Fecal concentration of Rhodococcus equi determined by quantitative polymerase chain reaction of rectal swab samples to differentiate foals with pneumonia from healthy foals

BACKGROUND

Diagnostic accuracy of real-time, quantitative PCR (qPCR) assays to quantify virulent Rhodococcus equi using rectal swab samples has not been systematically evaluated.

OBJECTIVE

To evaluate the accuracy of qPCR of rectal swab samples to differentiate foals with pneumonia from healthy foals of similar age from the same environment.

ANIMALS

One hundred privately owned foals born in 2021 from 2 farms in New York.

METHODS

An incident case-control study design was used. Rectal swabs were collected from all foals diagnosed with R. equi pneumonia at 2 horse-breeding farms (n = 47). Eligible pneumonia cases (n = 39) were matched by age to up to 2 healthy (n = 53) control foals; rectal swabs were collected from control foals on the day of diagnosis of the index case. DNA was extracted from fecal swabs and the concentration of virulent R. equi (ie, copy numbers of the virulence-associated protein A gene [vapA] per 100 ng fecal DNA) was estimated by qPCR.

RESULTS

The area under the ROC curve for qPCR of fecal swabs was 83.7% (95% CI, 74.9-92.6). At a threshold of 14 883 copies of vapA per 100 ng fecal DNA, specificity of the assay was 83.0% (95% CI, 71.7-92.4) and sensitivity was 79.5% (95% CI, 66.7-92.3).

CONCLUSIONS AND CLINICAL IMPORTANCE

Although fecal concentrations of virulent R. equi are significantly higher in pneumonic foals than healthy foals of similar age in the same environment, qPCR of rectal swabs as reported here lacks adequate diagnostic accuracy for clinical use.

Association of pneumonia with concentrations of virulent Rhodococcus equi in fecal swabs of foals before and after intrabronchial infection with virulent R. equi

Background

Intragastric administration of virulent Rhodococcus equi protects foals against subsequent experimental intrabronchial (IB) infection, but it is unknown whether R. equi naturally ingested by foals contributes to their susceptibility to pneumonia.

Hypothesis

Fecal concentration of virulent R. equi before IB infection with R. equi is positively associated with protection from pneumonia in foals.

Animals

Twenty‐one university‐owned foals.

Methods

Samples were collected from experimental studies. Five foals were gavaged with live, virulent R. equi (LVRE) at age 2 and 4 days; the remaining 16 foals were not gavaged with LVRE (controls). Fecal swabs were collected from foals at ages 28 days, immediately before IB infection. Foals were monitored for clinical signs of pneumonia, and fecal swabs were collected approximately 2 weeks after IB infection. Swabs were tested by quantitative PCR for concentration of virulent R. equi (ie, copy numbers of the virulence‐associated protein A gene [vapA] per 100 ng fecal DNA).

Results

Fecal concentrations of virulent R. equi (vapA) before IB infection were significantly (P < .05) lower in control foals (25 copies/100 ng DNA [95% CI, 5 to 118 copies/100 ng DNA) that developed pneumonia (n = 8) than in healthy control foals (n = 8; 280 copies/100 ng DNA; 95% CI, 30 to 2552 copies/100 ng DNA) or those gavaged with LVRE (707 copies/100 ng DNA, 95% CI, 54 to 9207 copies/100 ng DNA).

Conclusions and Clinical Importance

Greater natural ingestion of LVRE might contribute to protection against pneumonia among foals.

Novel potent IFN-γ-inducing CD8+ T cell epitopes conserved among diverse Bovine Viral Diarrhea Virus strains

Studies of immune responses elicited by Bovine Viral Diarrhea Virus (BVDV) vaccines have primarily focused on the characterization of neutralizing B cell and CD4+ T cell epitopes. Despite availability of vaccines for decades, BVDV prevalence in cattle remains largely unaffected. There is limited knowledge regarding the role of BVDV-specific CD8+ T cells in immune protection and indirect evidence suggests that they play a crucial role during BVDV infection. In this study, presence of BVDV-specific CD8+ T cells that are highly cross-reactive in cattle was demonstrated. Most importantly, novel potent IFN-γ-inducing CD8+ T cell epitopes were identified from different regions of BVDV polyprotein. Eight CD8+ T cell epitopes were identified from structural BVDV antigens: Erns, E1, and E2 glycoproteins. In addition, from nonstructural BVDV antigens: Npro, NS2-3, NS4A-B, and NS5A-B, twenty CD8+ T cell epitopes were identified. Majority of these IFN-γ-inducing CD8+ T cell epitopes were found to be highly conserved among more than two hundred strains from BVDV-1 and -2 genotypes. These conserved epitopes were also validated as cross-reactive since they induced high recall IFN-γ+ CD8+ T cell responses, ex vivo, in purified CD8+ T cells from BVDV-1- and -2-immunized cattle. Altogether, twenty-eight bovine MHC I-binding epitopes were identified from key BVDV antigens that can elicit broadly reactive CD8+ T cells against diverse BVDV strains. The data presented here will lay the groundwork for the development of a contemporary CD8+ T cell-based BVDV vaccine capable of addressing BVDV heterogeneity more effectively than current vaccines.

Complement Receptor 3, but not Fcγ Receptor III, abolishes the intracellular survival advantage of virulent Rhodococcus equi in murine macrophages

Complement receptor 3 (CR3) and Fc gamma receptor III (FcγRIII) are proposed to be essential for mediating Rhodococcus equi entry and killing in macrophages, respectively. Our objective was to investigate the role of each of these receptors in phagocytosis and intracellular replication of R. equi by macrophages. Wild-type (WT), CR3−/−, and FcγRIII−/− J774A.1 macrophages were infected with either virulent or avirulent opsonized R. equi. Quantitative culture was performed immediately post-infection (T0) and after 48 h (T48). Data were analyzed using mixed-effects modeling with the following outcomes: 1) ratio of inoculum:T0 (phagocytosis); and, 2) ratio of T48:T0 (intracellular survival). Additionally, WT, CR3−/−, and FcγRIII−/− macrophages were infected with virulent or avirulent GFP+ R. equi to confirm intracellular infection by confocal microscopy. Our results demonstrate that phagocytosis of either virulent or avirulent R. equi was unaffected by knocking out CR3 or FcγRIII, and imaging revealed that CR3−/− and FcγRIII−/− internalized both R. equi strains similarly to WT macrophages. As expected, intracellular survival in WT was significantly higher for virulent than avirulent R. equi. In CR3−/−, however, no significant difference in survival between virulent and avirulent strains was observed. Knocking out FcγRIII did not alter R. equi intracellular replication. Our findings demonstrate that CR3 is not necessary for R. equi infection and show that CR3 deletion eliminated the intracellular survival advantage of virulent strains. Last, FcγRIII-mediated phagocytosis does not improve intracellular killing as previously suggested.

Uptake and replication in Acanthamoeba castellanii of a virulent (pVAPA-positive) strain of Rhodococcus equi and its isogenic, plasmid-cured strain

Rhodococcus equi is a soil saprophytic bacterium and intracellular pathogen that causes pneumonia in foals. Strains of R. equi that are virulent in foals contain a plasmid that encodes a virulence-associated protein A (VapA) necessary for replication in macrophages. Because other intracellular pathogens survive and replicate inside amoebae, we postulated that the VapA-bearing plasmid (pVAPA) confers a survival advantage for R. equi against environmental predators like amoebae. To test this hypothesis, we compared phagocytosis by and survival in Acanthamoeba castellanii of isogenic strains of pVAPA-positive and pVAPA-negative R. equi. Phagocytosis of the pVAPA-negative strain by A. castellanii was significantly (P < 0.0001) greater than the pVAPA-positive strain. Intracellular replication of the pVAPA-positive strain in A. castellanii was significantly (P < 0.0001) greater than the pVAPA-negative strain during both 48 h and 9 days. These results indicate that the presence of the VapA plasmid reduces uptake and aids replication of R. equi in A. castellanii.

Vaccination of yearling horses against poly-N-acetyl glucosamine fails to protect against infection with Streptococcus equi subspecies equi

Strangles is a common disease of horses with worldwide distribution caused by the bacterium Streptococcus equi subspecies equi (SEE). Although vaccines against strangles are available commercially, these products have limitations in safety and efficacy. The microbial surface antigen β 1→6 poly-N-acetylglucosamine (PNAG) is expressed by SEE. Here we show that intramuscular (IM) injection alone or a combination of IM plus intranasal (IN) immunization generated antibodies to PNAG that functioned to deposit complement and mediate opsonophagocytic killing of SEE ex vivo. However, immunization strategies targeting PNAG either by either IM only injection or a combination of IM and IN immunizations failed to protect yearling horses against infection following contact with infected horses in an experimental setting. We speculate that a protective vaccine against strangles will require additional components, such as those targeting SEE enzymes that degrade or inactivate equine IgG.

In vitro evaluation of complement deposition and opsonophagocytic killing of Rhodococcus equi mediated by poly-N-acetyl glucosamine hyperimmune plasma compared to commercial plasma products

Background

The bacterium Rhodococcus equi can cause severe pneumonia in foals. The absence of a licensed vaccine and limited effectiveness of commercial R. equi hyperimmune plasma (RE‐HIP) create a great need for improved prevention of this disease.

Hypothesis

Plasma hyperimmune to the capsular polysaccharide poly‐N‐acetyl glucosamine (PNAG) would be significantly more effective than RE‐HIP at mediating complement deposition and opsonophagocytic killing (OPK) of R. equi.

Animals

Venipuncture was performed on 9 Quarter Horses.

Methods

The ability of the following plasma sources to mediate complement component 1 (C1) deposition onto either PNAG or R. equi was determined by ELISA: (1) PNAG hyperimmune plasma (PNAG‐HIP), (2) RE‐HIP, and (3) standard non‐hyperimmune commercial plasma (SP). For OPK, each plasma type was combined with R. equi, equine complement, and neutrophils isolated from horses (n = 9); after 4 hours, the number of R. equi in each well was determined by quantitative culture. Data were analyzed using linear mixed‐effects regression with significance set at P < .05.

Results

The PNAG‐HIP and RE‐HIP were able to deposit significantly (P < .05) more complement onto their respective targets than the other plasmas. The mean proportional survival of R. equi opsonized with PNAG‐HIP was significantly (P < .05) less (14.7%) than that for SP (51.1%) or RE‐HIP (42.2%).

Conclusions and Clinical Importance

Plasma hyperimmune to PNAG is superior to RE‐HIP for opsonizing and killing R. equi in vitro. Comparison of these 2 plasmas in field trials is warranted because of the reported incomplete effectiveness of RE‐HIP.

PNAG-specific equine IgG1 mediates significantly greater opsonization and killing of Prescottella equi (formerly Rhodococcus equi) than does IgG4/7

Prescottella equi (formerly Rhodococcus equi) is a facultative intracellular bacterial pathogen that causes severe pneumonia in foals 1-6 months of age, whereas adult horses are highly resistant to infection. We have shown that vaccinating pregnant mares against the conserved surface polysaccharide capsule, β-1 → 6-linked poly-N-acetyl glucosamine (PNAG), elicits opsonic killing antibody that transfers via colostrum to foals and protects them against experimental infection with virulent. R. equi. We hypothesized that equine IgG1 might be more important than IgG4/7 for mediating protection against R. equi infection in foals. To test this hypothesis, we compared complement component 1 (C1) deposition and polymorphonuclear cell-mediated opsonophagocytic killing (OPK) mediated by IgG1 or IgG4/7 enriched from either PNAG hyperimmune plasma (HIP) or standard plasma. Subclasses IgG1 and IgG4/7 from PNAG HIP and standard plasma were precipitated onto a diethylaminoethyl ion exchange column, then further enriched using a protein G Sepharose column. We determined C1 deposition by enzyme-linked immunosorbent assay (ELISA) and estimated OPK by quantitative microbiologic culture. Anti-PNAG IgG1 deposited significantly (P < 0.05) more C1 onto PNAG than did IgG4/7 from PNAG HIP or subclasses IgG1 and IgG4/7 from standard plasma. In addition, IgG1 from PNAG HIP mediated significantly (P < 0.05) greater OPK than IgG4/7 from PNAG HIP or IgG1 and IgG4/7 from standard plasma. Our findings indicate that anti-PNAG IgG1 is a correlate of protection against R. equi in foals, which has important implications for understanding the immunopathogenesis of R. equi pneumonia, and as a tool for assessing vaccine efficacy and effectiveness when challenge is not feasible.

Potential energy surfaces for oxygen adsorption, dissociation, and diffusion at the Pt(321) surface

We report a first-principles, periodic supercell analysis of oxygen adsorption, diffusion, and dissociation at the kinked Pt(321) surface. Binding energies and binding site preferences of isolated oxygen atoms and molecules have been determined, and we show that both atomic and molecular oxygen prefer binding in bridge sites involving coordinatively unsaturated kink Pt atoms. Binding energies of atomic and molecular oxygen in different sites correlate well with the average metallic Pt coordination number of Pt atoms forming each site, although differences exist between adsorbates in symmetrically similar sites due to the inherent chirality of the surface. Atomic O in the strongest binding bridge sites experiences relatively small energy barriers for diffusion to neighboring sites compared to O on Pt(111). However, due to the structure of the surface, O diffusion is only rapid between different sites around the kink Pt atom, whereas the effective long-range tracer diffusion, as determined from a simple course-grain model, is shown to be anisotropic and slower than on the Pt(111) surface. Four dissociation pathways for O(2) at low coverage are also reported and found to be in agreement with experimental observations of facile dissociation, even at low temperature.

Colour Doppler and duplex sonography and angiography of the carotid artery bifurcations. Prospective, double-blind study

We undertook a prospective double-blind study of 128 carotid artery bifurcations using colour Doppler and duplex sonography and angiography. Sixty-four patients with cerebrovascular events were admitted for angiography. All underwent sonography within 24 h of angiography. Standard duplex sonography and colour Doppler imaging without spectral analysis were performed, on the same device, by two sonographers, using defined morphological and haemodynamic criteria. Digital radiological data on vessel diameter were interpreted independently by two radiologists. The two sonographic methods gave similar grading of stenosis, compared to angiography, with an accuracy ranging from 96% in severe to 83% in minor stenoses. Colour Doppler studies gave better area measurements than standard duplex sonography, except for major stenoses. Discrepancies between ultrasonography and angiography were due mainly to minor stenoses and large plaques of calcification on the vessel walls, which masked very segmental 70% stenoses in 2 cases. Angiography is limited by its own resolution, does not show uncalcified vessel walls and does not give cross-sectional data. It would therefore be inappropriate for showing small plaques, the full extent of ectasia or for defining the carotid bulb accurately. The advantages of colour methods were in investigating sinuous or deep vessels and hypoechoic plaques. Analysis of the residual lumen of a stenosis and its extent could be determined more rapidly. Haemodynamic quantification of stenoses by standard duplex sonography may be difficult because of limited sample volume and error in estimation of angle, whereas colour Doppler allows semiquantitative estimation of haemodynamics.(ABSTRACT TRUNCATED AT 250 WORDS)