Ovine opsonins for Staphylococcus aureus cell wall and pseudocapsule.

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.