Administration of commercial Rhodococcus equi specific hyperimmune plasma results in variable amounts of IgG against pathogenic bacteria in foals

Abstract

Rhodococcus equi is the most common cause of pneumonia in young foals. A vaccine is not available and the use of R equi-specific hyperimmune plasma (HIP) is common. Despite its widespread use, the efficacy of HIP in preventing disease remains controversial. The objectives of this study were (1) to evaluate the virulence associate protein A (VapA)-specific IgG and IgG subclasses in commercially available R equi HIP and (2) to evaluate serum VapA-specific IgG and IgG subclasses in foals following administration of commercial R equi HIP. Three different lots from four commercial R equi HIP were sampled. VapA-specific IgG and IgG subclasses were evaluated in all samples using an ELISA. Serum was collected from newborn foals either after commercial R equi HIP was administered (n=97) or not (n=70). Serum was also collected from each mare. Administration of HIP significantly (P<0.001) increased VapA-specific IgGs in recipient foals, however, there was a marked variation in VapA-specific IgGs in foals receiving the same product. VapA-specific IgGs were significantly different (P<0.001) between products and varied between lots, with coefficients of variation ranging from 17 to 123 per cent. These results may explain previously reported disparities in HIP efficacy.

Rhodococcus equi hyperimmune plasma decreases pneumonia severity after a randomised experimental challenge of neonatal foals

“…The variations seen in VapA-specific antibodies between bags of HIP and between foals after HIP administration were consistent with those previously reported for this product (Sanz and others 2014b). As expected, foals that received HIP had significantly higher serum VapA-specific IgG and IgGb for the entire duration of the study.…”

“…The number of foals selected was, however, sufficient to reach adequate power (>0.8) in the majority of the parameters evaluated. While this study shows a protective effect of early HIP administration against the development of clinical rhodococcal pneumonia, these results cannot be extrapolated to all products available in the market, as high variability in the antibody content between and among HIP products exists (Sanz and others 2014b). In addition, unlike the foals in this study that were challenged one day, foals under natural conditions are constantly exposed to R equi.…”

“…As expected, foals that received HIP had significantly higher serum VapA-specific IgG and IgGb for the entire duration of the study. This was predicted as IgGb is the predominant subclass in commercial HIP licensed for R equi in the USA (Sanz and others 2014b) and endogenous synthesis of IgGb does not begin until foals are at least two months of age (Sheoran and others 2000). Similarly, serum VapA-specific IgGa was initially higher after HIP administration; however, because of endogenous production that occurs as early as five weeks of age (Sheoran and others 2000, Sanz and others 2014a) as a response to infection (Sanz and others 2014a), control foals had significantly higher IgGa towards the end of the study.…”

“…The purity of the protein was assessed by SDS-PAGE (Bio-Rad, Philadelphia, Pennsylvania, USA) (Sanz and others 2014b). …”

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

“…Thus, there is a great need for prevention of R. equi pneumonia. No commercially available vaccines against R. equi exist, such that prevention of pneumonia is based primarily on transfusion of plasma that is hyperimmune to R. equi (RE‐HIP) . Transfusion of RE‐HIP, however, is not completely effective in decreasing the incidence of R. equi pneumonia at horse breeding farms .…”