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

J Vet Intern Med. 2019 May;33(3):1493-1499. doi: 10.1111/jvim.15511. Epub 2019 Apr 29.

Abstract

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.

Keywords: Rhodococcus equi; complement; horse; neutrophils; opsonophagocytic killing; plasma.

MeSH terms

  • Acetylglucosamine / immunology*
  • Actinomycetales Infections / immunology
  • Actinomycetales Infections / veterinary*
  • Animals
  • Antibodies, Bacterial / blood
  • Complement C1 / immunology
  • Female
  • Horse Diseases / immunology
  • Horse Diseases / microbiology
  • Horses / immunology
  • Male
  • Neutrophils
  • Plasma / immunology
  • Rhodococcus equi / immunology*

Substances

  • Antibodies, Bacterial
  • Complement C1
  • poly-N-acetyl glucosamine
  • Acetylglucosamine