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.
Authors: Kahn Susanne K, Cywes-Bentley Colette, Blodgett Glenn P, Canaday Nathan M, Turner-Garcia Carly E, Vinacur Mariana, Cortez-Ramirez Sophia C, Sutter Patrick J, Meyer Sarah C, Bordin Angela I, Vlock Daniel R, Pier Gerald B, Cohen Noah D
Journal: PloS one
Summary
Rhodococcus equi pneumonia remains a significant challenge in foal health, yet evidence supporting hyperimmune plasma (HIP) transfusion has been limited. Researchers at two large Quarter Horse breeding farms randomised 233 newborn foals to receive 2 L of HIP derived from adult donors immunised either with live R. equi or a conjugate vaccine targeting the surface polysaccharide poly-N-acetyl glucosamine (PNAG), then measured antibody titres against VapA (virulence-associated protein A) and PNAG alongside complement component C1q deposition using ELISA and linked these to pneumonia outcomes. Foals receiving R. equi HIP showed approximately six-fold higher odds of developing pneumonia when VapA antibody activity fell below the population median (P = 0.0005), whilst in the PNAG HIP group, odds increased threefold for low PNAG antibodies and elevenfold for low C1q deposition (P = 0.0034). Critically, functional antibody activity—measured by C1q complement fixation—proved a stronger protective indicator than antibody titre alone, suggesting that plasma quality and antibody functionality, not merely volume, drive protection against both subclinical and clinical disease. For practitioners selecting or evaluating HIP donors, these findings underscore the importance of assessing both antibody titre and functional capacity, particularly complement-fixing activity, as surrogate markers of protective efficacy.
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Practical Takeaways
- •Hyperimmune plasma transfusion effectiveness depends on antibody quality and activity level, not just volume — verify that donated plasma has adequate VapA or PNAG antibody titres before use
- •When using PNAG-based HIP, ensure donors have high-quality functional antibodies (measured by C1q deposition), as these provide significantly stronger protection than basic antibody presence
- •Consider testing foals' post-transfusion antibody levels to identify high-risk individuals who may need additional preventive strategies despite receiving HIP
Key Findings
- •Foals with VapA antibody activity below the population median had approximately 6-fold higher odds of pneumonia when receiving RE HIP (P=0.0005)
- •PNAG HIP-transfused foals with antibody activity below the median had 3-fold higher odds of pneumonia (P=0.0347), and 11-fold higher odds when C1q deposition was below median (P=0.0034)
- •Functional antibodies (those with C1q deposition capability) were a stronger predictor of protection than antibody presence alone
- •Antibody activity level rather than volume is critical for protection against both clinical and subclinical R. equi pneumonia in field conditions