Proteolytic cleavage of bovine IgG by hypodermin A, a serine protease of Hypoderma lineatum (Diptera: Oestridae).

Cattle grub larvae are able to survive a lengthy 8 1/2-mo internal migration within the naive bovine host connective tissues. Larval survival is observed even in the presence of host immunological responses to principal parasite proteins. In this study, data are presented that suggest that a digestive enzyme, hypodermin A, of the first-instar larvae effectively cleaves bovine immunoglobulin G in vitro. A (fab)'2 fragment is produced, and the heavy-chain fragments associated with the cleaved fc piece remain intact. Hypodermin A is not specific for bovine IgG as other species' IgGs are also degraded as are other bovine proteins. Destruction of the biological activity of bovine immunoglobulin G by hypodermin A suggests a potential parasite escape mechanism that may contribute to the survival of first-instar larvae within the bovine host.