Biochemical and immunochemical characterization of 125I-labeled cuticle components of Haemonchus contortus

Anthelmintic activity of Leucaena leucocephala protein extracts on Haemonchus contortus

The objective of this study was to evaluate the effects of protein extracts obtained from the plant Leucaena leucocephala on the nematode parasite Haemonchus contortus. The seeds, shell and cotyledon of L. leucocephala were separated and their proteins extracted using a sodium phosphate buffer, and named as TE (total seed extract), SE (shell extract) and CE (cotyledon extract). Soluble protein content, protease, protease inhibitory and chitinase activity assays were performed. Exsheathment inhibition of H. contortus larvae were performed at concentrations of 0.6 mg mL-1, and egg hatch assays were conducted at protein concentrations of 0.8, 0.4, 0.2, 0.1 and 0.05 mg mL-1. The effective concentration for 50% hatching inhibition (EC50) was estimated by probit. Different proportions of soluble proteins, protease and chitinase were found in TE and CE. Protease inhibitory activity was detected in all extracts. The EC50 of the CE and TE extracts were 0.48 and 0.33 mg mL-1, respectively. No ovicidal effects on H. contortus were detected in SE extracts, and none of the protein extracts demonstrated larvicidal effects on H. contortus. We therefore conclude that protein extracts of L. leucocephala had a detrimental effect on nematode eggs, which can be correlated with the high protease and chitinase activity of these extracts.

An AC-5 cathepsin B-like protease purified from Haemonchus contortus excretory secretory products shows protective antigen potential for lambs

The immunogenic properties of cysteine proteases obtained from excretory/secretory products (ES) of Haemonchus contortus were investigated with a fraction purified with a recombinant H. contortus cystatin affinity column. The enrichment of H. contortus ES for cysteine protease was confirmed with substrate SDS-PAGE gels since the cystatin-binding fraction activity was three times higher than total ES, despite representing only 3% of total ES. This activity was inhibited by a specific cysteine protease inhibitor (E64) and by recombinant cystatin. The one-dimensional profile of the cystatin-binding fraction displayed a single band with a molecular mass of 43 kDa. Mass spectrometry showed this to be AC-5, a cathepsin B-like cysteine protease which had not been identified in ES products of H. contortus before. The cystatin binding fraction was tested as an immunogen in lambs which were vaccinated three times (week 0, 2.5 and 5), challenged with 10 000 L3 H. contortus (week 6) before necropsy and compared to unvaccinated challenge controls and another group given total ES (n = 10 per group). The group vaccinated with cystatin-binding proteins showed 36% and 32% mean worm burden and eggs per gram of faeces (EPG) reductions, respectively, compared to the controls but total ES was almost without effect. After challenge the cystatin-binding proteins induced significantly higher local and systemic ES specific IgA and IgG responses.

Haemonchus contortus glycoproteins contain N-linked oligosaccharides with novel highly fucosylated core structures

Structural studies on the N-linked oligosaccharides of Haemonchus contortus, an economically important nematode that parasitizes domestic ruminants, have revealed core fucosylation of a type not previously observed in any eukaryotic glycoprotein. Mass spectrometric analyses were performed on detergent extracts of homogenized adult H. contortus and on purified H11, a glycoprotein isolated from intestinal brush borders which has been previously shown to be an effective vaccine antigen. The major N-linked glycans identified in the present study have up to three fucose residues attached to their chitobiose cores. The fucoses are found at the 3- and/or 6-positions of the proximal GlcNAc and at the 3-position of the distal GlcNAc. The latter substitution is unique in N-glycans. Most anti-H11 monoclonal antibodies are known to recognize carbohydrate epitopes, and it is possible that the newly discovered multifucosylated core structures are highly immunogenic in this glycoprotein.

The role of the sheath in resistance of Haemonchus contortus infective-stage larvae to proteolytic digestion

Surface iodinated larvae of Haemonchus contortus were incubated in the presence of the fungal protease, proteinase K, and proteolysis quantified by scintillation counting of released radioactivity. No radioactivity was released from live ensheathed infective-stage larvae (L3(2M)). In contrast, 58% of the radioactivity was released from ecdysed, second molt (2M) cuticles (sheaths) of L3(2M) and 48% from live exsheathed third-stage larvae (L3). When L3(2M) larvae were killed by heat (80 degrees C for 10 min) prior to proteinase K incubation, 61% of the radioactivity was released, whereas less than 7% was released from larvae killed by the metabolic inhibitors NaN3 or KCN. Proteinase K released 44% of the radioactivity from live L3(2M) larvae which had been preincubated with 1% sodium dodecylsulfate (SDS), whereas no radioactivity was released from L3(2M) larvae preincubated with either 1% Triton X-100, 0.2% CTAB, 50% methanol, 50% ethanol, or water. Following incubation with proteinase K, only L3(2M) larvae which had been heat-killed or preincubated with SDS showed visible damage to the sheath. Material released from L3(2M) larvae by exposure to either heat or SDS contained a 98,000 M(r) protein by SDS-PAGE autoradiography. These results indicate that viable L3(2M) larvae are resistant to attack by proteinase K and that this resistance is dependent on structural properties of the sheath.

Isotype-specific antibody responses to the surface-exposed antigens of adult and larval stages of Dictyocaulus viviparus in infected and vaccinated calves

The antibody responses to the surface-exposed antigens of living larval and adult Dictyocaulus viviparus were measured by quantitative immunofluorescence using sera from calves infected with, or vaccinated against, the parasite. In infected animals, the surface of the sheath of the third-stage larvae (L3) (retained cuticle of second-stage larvae (L2)) proved highly immunogenic despite the fact that it is thought to be shed prior to parasite penetration of the host intestine. When responses to the surface of exsheathed larvae (L3 cuticle) were measured, a high level of heterophile IgM antibody was detected in the serum of animals that had not been previously exposed to the parasite and, following infection, a specific IgG response was detected against the exsheathed L3 surface. The antibody response, however, was less marked than that observed against the intact L3 sheath. Responses of patently infected animals to the adult surface showed an initial IgM response that was superseded with time by IgG1 and IgG2 responses. Vaccinated animals showed only low level responses to the surfaces of the L3 sheath, L3 cuticle and adult stages following immunisation with two doses of irradiated larvae. The immunised animals produced a strong antibody response to the larval surface antigens following challenge with infective larvae but they failed to produce antibody to the surface of adult parasites. These results show that the surfaces of all the stages of D. viviparus examined are immunogenic in infected calves and, depending on the developmental stage, infection regime, or time of infection, high levels of parasite-specific IgG1 or IgM are stimulated. It has previously been shown that significant levels of protective immunity can be obtained in naive animals following passive transfer of serum from infected calves. Thus, the antibody responses detected in the work reported here may be of relevance in protective immunity against dictyocaulosis.

Biochemistry of the nematode cuticle: relevance to parasitic nematodes of livestock

The cuticle of nematodes is a thin, flexible outer covering composed primarily of protein with trace amounts of lipid and carbohydrate. There has been considerable recent interest in the biochemistry, immunology and molecular biology of the cuticle of parasitic nematodes because of its role as an interface between parasite and host. The cuticle consists of: (1) collagen-like proteins that form the medial and basal layers; (2) non-collagen proteins that form the epicuticular and external cortical regions; (3) non-structural proteins associated with the external surface. The collagen-like proteins are solubilized by reducing agents, have molecular weights of 30-120 kDa and exhibit stage and species variations. Nematode collagen genes, however, code only for proteins with molecular weights of 30 kDa. The non-collagenous proteins, referred to as cuticlin, exhibit unusual chemical properties as indicated by their resistance to solubilization even under strongly denaturing conditions. Recent studies of Ascaris suum have demonstrated the presence of tyrosine-derived cross-links, dityrosine and isotrityrosine, that may form the linkage between subunits in assemblage of the collagenous and noncollagenous structural components of the cuticle. A peroxidase enzyme has been implicated in the synthesis of these cross-links. Recent 125I labeling studies of Haemonchus contortus have identified and characterized stage-specific proteins on the cuticular surface.