Protective immunity to Haemonchus contortus induced by immunoaffinity isolated antigens that share a phylogenetically conserved carbohydrate gut surface epitope.

Abstract

Whole gut homogenates of the blood-sucking nematode Haemonchus contortus induce protective immunity in goats, and some of these gut Ag are conserved among related parasitic nematode species. To identify gut Ag that induce protective immunity and have phylogenetically conserved epitopes, mAb were made to gut-surface Ag of H. contortus. Forty-nine mAb reacted with microvilli of the parasite gut. Two of these mAb (42/10.6.1 and 42/53.3.5) were analyzed here. Both of the mAb bound to the microvillar surface of freshly isolated gut, and each mAb recognized carbohydrate epitopes, based on sensitivity to periodate oxidation. The 42/10.6.1 epitope occurred on at least 18 proteins in Western blots and in several H. contortus tissues. Proteins recognized by this mAb localized to membrane and excretory/secretory fractions of the worm. This epitope was also identified on the gut and other tissues and multiple proteins of related adult and larval nematodes, including larval Ancylostoma caninum and a mixed population of the free-living nematode Caenorhabditis elegans. In contrast, the 42/53.3.5 mAb bound to the gut surface and recognized proteins of 100 and 46 kDa from adult H. contortus gut. Four proteins of 100, 52, 46, and 30 kDa were isolated from the 42/53.3.5 immunoaffinity columns, and except for the 30-kDa protein, each was recognized by both the 42/10.6.1 and 42/53.3.5 mAb. Epitopes recognized by each mAb were distinct from one another and phosphorylcholine. When used to immunize goats, Ag isolated by both mAb induced protection that significantly (p < 0.05) reduced total worm counts after challenge infections compared with the control groups.