Antibody activities in hyperimmune plasma against the Rhodococcus equi virulence -associated protein A or poly-N-acetyl glucosamine are associated with protection of foals against rhodococcal pneumonia.

The efficacy of transfusion with hyperimmune plasma (HIP) for preventing pneumonia caused by Rhodococcus equi remains ill-defined. Quarter Horse foals at 2 large breeding farms were randomly assigned to be transfused with 2 L of HIP from adult donors hyperimmunized either with R. equi (RE HIP) or a conjugate vaccine eliciting antibody to the surface polysaccharide β-1→6-poly-N-acetyl glucosamine (PNAG HIP) within 24 hours of birth. Antibody activities against PNAG and the rhodococcal virulence-associated protein A (VapA), and to deposition of complement component 1q (C՛1q) onto PNAG were determined by ELISA, and then associated with either clinical pneumonia at Farm A (n = 119) or subclinical pneumonia at Farm B (n = 114). Data were analyzed using multivariable logistic regression. Among RE HIP-transfused foals, the odds of pneumonia were approximately 6-fold higher (P = 0.0005) among foals with VapA antibody activity ≤ the population median. Among PNAG HIP-transfused foals, the odds of pneumonia were approximately 3-fold (P = 0.0347) and 11-fold (P = 0.0034) higher for foals with antibody activities ≤ the population median for PNAG or C՛1q deposition, respectively. Results indicated that levels of activity of antibodies against R. equi antigens are correlates of protection against both subclinical and clinical R. equi pneumonia in field settings. Among PNAG HIP-transfused foals, activity of antibodies with C՛1q deposition (an indicator of functional antibodies) were a stronger predictor of protection than was PNAG antibody activity alone. Collectively, these findings suggest that the amount and activity of antibodies in HIP (i.e., plasma volume and/or antibody activity) is positively associated with protection against R. equi pneumonia in foals.
Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: Gerald B. Pier (GBP) is an inventor of intellectual properties [human monoclonal antibody to PNAG and PNAG vaccines] that are licensed by Brigham and Women’s Hospital to Alopexx Vaccine, LLC, an entity in which GBP also holds equity. As an inventor of intellectual properties, GBP also has the right to receive a share of licensing-related income (royalties, fees) through Brigham and Women’s Hospital from Alopexx Vaccine, LLC. GBP’s interests were reviewed and are managed by the Brigham and Women’s Hospital and Partners Health care in accordance with their conflict of interest policies. Colette Cywes-Bentley (CC-B) is an inventor of intellectual properties [use of human monoclonal antibody to PNAG and use of PNAG vaccines] that are licensed by Brigham and Women’s Hospital to Alopexx Vaccine, LLC. As an inventor of intellectual properties, CC-B also has the right to receive a share of licensing-related income (royalties, fees) through Brigham and Women’s Hospital from Alopexx Vaccine, LLC. Daniel R. Vlock is the Chief Executive Officer of ALOPEXX Vaccines and owns the rights to the PNAG vaccine. Dr. Vlock had no role in the design or analysis of the study. SC Meyer and PJ Sutter work for MG Biologics that produced the plasma and thus might have potential earnings; however, they had no part in the design or analysis of the study. Drs. Glenn Blodgett and Nathan Canaday are employees of the 6666 Ranch and Dr. Carly Turner-Garcia is employed by the Lazy E Ranch. Sarah Meyer and Patrick Sutter are employed by Mg Biologics, Inc. and Dr. Daniel Vlock is employed by ALOPEXX Vaccines. The 6666 Ranch, Lazy E Ranch, Mg Biologics, and ALOPEXX provided support in the form of salaries, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. This does not alter our adherence to PLOS ONE policies on sharing data and materials.