Rejection of heterologous nematodes by sheep immunized with larval or adult Trichostrongylus colubriformis.

Sheep immunized by truncated larval infections or by the adoptive transfer of adult Trichostrongylus colubriformis were subsequently challenged with single infections of T. colubriformis, Nematodirus spathiger, Haemonchus contortus or Ostertagia circumcincta or combinations of the parasites. Sheep vaccinated with larval infections were > 90% protected by 4 days after challenge (DAC) against T. colubriformis L3 given in a single or combined infection, whereas no significant protection was exhibited against a single-species infection with the unrelated nematodes N. spathiger or O. circumcincta. Sheep challenged with T. colubriformis together with N. spathiger or O. circumcincta were equally protected against both intestinal nematodes, but O. circumcincta was not affected. Sheep immunized with adult T. colubriformis and challenged with a combined infection of T. colubriformis, N. spathiger and H. contortus expelled around 40 and 80% of the intestinal parasites by 4 and 11 DAC, respectively, but showed no protection against the abomasal parasite, H. contortus. The results confirm the previous findings on 'self-cure' and the non-specific rejection of unrelated parasites living in the same or downstream niches in the gut when the nematode used to induce immunity is included in the challenge infection. The results also indicate that even though L3 antigens effectively elicited the non-specific rejection, antigens produced by L4 and later stages could also induce rejection of unrelated worms in the second week after infection.

The isolation, characterization and cloning of a globin-like, host-protective antigen from the excretory-secretory products of Trichostrongylus colubriformis.

An 18-kDa component from the excretory-secretory (ES) products of adults of Trichostrongylus colubriformis was isolated and characterized, and was shown to induce 60-84% protection of guinea pigs from challenge infection following a single intraperitoneal injection. Amino-terminal sequence analysis of gel-purified protein enabled oligonucleotides to be synthesized and used to screen a lambda gt10 cDNA library made from young adult worm mRNA, and to synthesize full-length clones from cDNA using the polymerase chain reaction (PCR). The full-length clones coded for a 20-kDa precursor protein of 173 amino acids which had a strongly hydrophobic leader sequence of 15 residues. The mature protein sequence of 158 amino acid residues was rich in charged amino acids (32%), including 8 oppositely charged pairs of amino acids. The protein sequence contained no half-cystine residues and no potential N-glycosylation sites. Unlike 2 other fully characterized ES components which are expressed only in the parasitic stages, mRNA coding for the 20-kDa component was present in both the parasitic and free-living stages of T. colubriformis. The parasite protein had approximately 20% identity with globins from human and from the larvae of the insect Chironomus thummi thummi. The homology included the invariant distal histidine and phenylalanine, and a number of other residues highly conserved in globins.

Effects of Freund's adjuvants on local, draining and circulating lymphocyte populations in sheep.

Lymphatic cannulation and serial biopsy were used to examine changes in cell traffic and lymphocyte populations after injection of adjuvant in order to explain the mechanisms of the subversive effect that Freund's adjuvants (FA) have on protective immunity against nematode parasites in sheep. Within 4 days of intradermal injection of complete or incomplete FA into sheep there was a selective depletion of the T19+ TCY gamma delta+ T lymphocyte subpopulation from efferent lymph draining the local lymph node. Transient depletion of CD8+, T19+ and CD5+ cells from jugular blood was evident at day 2. The adjuvant-induced granuloma was a connective tissue/macrophage/T lymphocyte phenomenon, with no B cell follicles, and the T cell content continued to increase for the 21 days. The early granuloma (days 2-4) contained a disproportionate number of T19+ gamma delta + lymphocytes. It appeared that the adjuvants induced selective sequestration of this T cell subset during the initial period of granuloma formation.

Characterization, cloning and host-protective activity of a 30-kilodalton glycoprotein secreted by the parasitic stages of Trichostrongylus colubriformis.

The helminth Trichostrongylus colubriformis is a parasitic nematode infecting the small intestine of sheep. We report the isolation and characterization of a 30-kDa glycoprotein capable of partially protecting guinea-pigs against the parasite. This glycoprotein is secreted by the L4 and adult parasitic stages of the worm. The sequence of three separate cDNA clones predicts the polypeptide to be about 15 kDa, with four N-linked carbohydrate chains and an internal disulphide bond. The clones also indicate the existence of sequence variability in this antigen. Limited sequence homology to a porcine intestinal peptide suggests an influence on host gut physiology.