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Updated: Aug 18, 2026

Opsonophagocytic Killing Assay to Assess Immunological Responses Against Bacterial Pathogens
Published on: April 5, 2019
Ovine opsonins for Staphylococcus aureus cell wall and pseudocapsule
1CSIRO, Division of Animal Health, Armidale, New South Wales, Australia.
Abstract:
Blood serum, milk whey and purified IgG1 and IgG2 antibody preparations from sheep immunised with live or killed Staphylococcus aureus vaccines were assayed for opsonising activity against S aureus using ovine mammary neutrophils as effector cells. Serum had much higher levels of opsonins than whey; whey did not inhibit the potent opsonising activity of hyperimmune serum. IgG1 antibodies against cell wall antigens of in vitro-grown S aureus and pseudocapsular antigens of in vivo-grown S aureus had low opsonising activity. IgG2 antibody against in vitro-grown S aureus surface antigens had significantly greater opsonising activity than IgG1 of this specificity. The most powerful opsonising activity was associated with IgG2 antibody against the pseudo-capsular antigens produced by S aureus grown under in vivo, or simulated in vivo cultural conditions.
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