The induction of slelctive immunological unresponsiveness in cells of blood and lymphoid tissue during primary infection of sheep with the abomasal nematode, Haemonchus contortus

The B cell dependence of Haemonchus contortus antigen-induced lymphocyte proliferation

The proliferative responses of ovine lymphocytes to soluble antigens of third-stage larvae of Haemonchus contortus (HcAg) were examined in vitro. Lymphocytes in mononuclear cell cultures responded consistently to HcAg even if the lambs were naive to H. contortus. Lymphocytes from sheep that were immune to reinfection with H. contortus also consistently responded to HcAg with a response significantly greater than that recorded from naive lambs. When the responses of T cell or B cell enriched fractions were examined, neither enriched cell population responded to HcAg, even though the T cell populations were shown to contain monocytes by histochemistry. Studies using the accessory cell dependent T cell mitogen Con A demonstrated that such T cell enriched populations had normal Con A-induced responses compared to unfractionated mononuclear cells. In addition, neither the T cell nor B cell fractions responded to HcAg in the presence of autologous mononuclear cells which contained monocytes and dendritic cells. Responses to HcAg in the T cell enriched population were restored, however, by the presence of mononuclear cells that were cultured with HcAg for 48 hours and then irradiated before the addition of the T cells. These results were seen with cells from both H. contortus naive lambs and immune sheep. This provides evidence that B cells and not dendritic cells or monocytes are acting as antigen presenting cells in Haemonchus antigen-induced lymphocyte responses in both naive lambs and immune sheep.

The same fractions of Haemonchus contortus soluble antigen induce lymphocyte responses in naive lambs and immune sheep

Soluble antigen extracted from third stage larvae of Haemonchus contortus was divided into fractions based on molecular weight by sodium dodecyl sulphate polyacrylamide gel electrophoresis and electrotransferred to nitrocellulose. Infection immunised adult sheep and H contortus naive lambs were used to examine the lymphocyte responses to these fractions in vitro. The results demonstrate that the same two fractions induced the strongest responses in both groups of animals.

Immunity to Haemonchus contortus and the cellular response to helminth antigens in the mammary gland of non-lactating sheep

Cellular exudates induced by infusion with helminth antigens were examined in non-lactating mammary glands of ewes immune to infection with the abomasal nematode, Haemonchus contortus. Secondary immunological responsiveness was expressed in two ways. Firstly, antigens from adult H. contortus elicited larger eosinophil-rich cellular exudates in immune compared to non-immune ewes. In this situation, secondary responsiveness in the mammary gland must have been generated through abomasal infection with the parasite. Secondly, repeated infusion with the antigens from adult H. contortus increased the size of cellular exudates in both immune and non-immune ewes. Eosinophils predominated but numbers of macrophages and lymphocytes were also increased. In this second situation, secondary responsiveness must have been either supplemented in immune ewes or derived completely in non-immune ewes by contact with helminth antigens through the mammary gland. The helminth antigens which induce eosinophil exudates in the mammary gland may not be potently protective against H. contortus. Furthermore, eosinophil exudation may not be an in vivo correlate of immunity which is directly useful for discriminating protective antigens and applicable to vaccine development. Infusion with antigens from adult forms of either H. contortus or Trichostrongylus colubriformis elicited cellular exudates equally well in immune ewes primed by infusion with H. contortus adult antigens 7 days beforehand. In addition, antigens from infective larvae of H. contortus elicited cellular exudates more potently than antigens from adult worms. However, vaccination with irradiated larvae has shown that species-specific protective immunity for H. contortus is stronger than cross-protective immunity conferred by T. colubriformis.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross-immunity between Haemonchus contortus and Trichostrongylus colubriformis in sheep

Cross-protective immunity between the nematode parasites, Haemonchus contortus and Trichostrongylus colubriformis, was examined in sheep vaccinated with irradiated larvae of either species. Secondary immunological responsiveness stimulated in this manner protected only against challenge infection with the species used for vaccination. Significant cross-protective immunity was not observed. Titres of serum antibody to an extract of adult but not infective larval T. colubriformis reflected the specificity for protective immunity. Immediate hypersensitivity skin reactions to nematode extracts did not reflect the antigen-specificity for protective immunity.

Advances in immunoparasitology

A selective review of the advances in immunoparasitology is presented. It is selective simply because it is not feasible to embrace the whole field of parasitology within the compass of a single review paper, for if it were attempted, it would suffer undue abbreviation. Emphasis is placed on the advances in helminthology and especially the gastro-intestinal parasites of ruminants, an obvious selection because of the interests of the author. Reviews are always somewhat retrospective in outlook; to write a review at the present time is especially foolhardy since developments in biology are such that totally new concepts can arise almost overnight, as it were. This is a particularly healthy state, and the discipline of parasitology is caught up in the application and interpretation of molecular biological considerations. "Parasitism" is a field of increasing importance and challenge.

Immunological unresponsiveness of lambs to infection with Haemonchus contortus. Modulation of responsiveness by exposure to soluble larval antigen

The in vitro transformation of lymphocytes in the presence of antigen was used to assay the response of lambs to antigens of Haemonchus contortus. Neither uninfected lambs nor lambs infected with H. contortus up to 9 weeks of age developed in vitro lymphocyte responsiveness to antigen. A slight and transient increase in reactivity was demonstrable in some of the infected lambs when these were reinfected with H. contortus at 26 weeks of age. This lack of responsiveness could be modulated through the exposure of lambs, early in neonatal life, to multiple parenteral injections of soluble third stage larval antigen of H. contortus. Thus, antigen specific responses were apparent in the lymphocytes from 21-week-old lambs if these were injected with antigen when 2 to 17 weeks of age. In particular, marked antigen specific reactivity developed in 19- or 24-week-old lambs if such lambs were injected with antigen on five occasions over the first 6 weeks of life and subsequently infected with H. contortus when 7 weeks old. This responsiveness was enhanced when the lambs were reinfected with H. contortus at 26 weeks of age.

Immunological unresponsiveness of lambs to infection with Haemonchus contortus. Effect of infection in the ewe on the subsequent responsiveness of lambs

Specific antigen-induced lymphocyte transformation in vitro and haemagglutinating antibody responses were absent from lambs infected with Haemonchus contortus. However, when lambs were injected with soluble third stage larval antigen of H. contortus, given on five occasions during the first 6 weeks of life, specific antigen-induced lymphocyte transformation and haemagglutinating antibodies were induced to the antigen. In particular, a periparturient increased susceptibility to infection and the resultant presence of heavy infections with H. contortus in ewes appeared to prime their lambs to respond and marked lymphocyte transformation was observed in antigen injected lambs born of heavily infected ewes. The enhancement of this response was associated with the colostral transfer of as yet unidentified factors. The superimposition of an infection with H. contortus in lambs which had been stimulated to respond to antigen, suppressed the in vitro responsiveness of their lymphocytes. Although individual variation was apparent, a direct correlation between the presence of in vitro antigen-induced lymphocyte transformation to third stage larval antigen and susceptibility to infection occurred.

Immune recognition of Echinococcus granulosus. 1. Parasite-activated, primary transformation by normal murine lymph node cells

Culture of murine lymph node cells together with living protoscolices of Echinococcus granulosus is described. The presence of the parasite induced potent blastic transformation in lymphocytes of unimmunized mice as indicated by tritiated thymidine incorporation. The response was markedly reduced by killing the parasite immediately prior to culture. No blastogenic activity was detectable in supernatants from living parasites cultured alone. Protoscolices from artificially infected syngeneic mice were effective stimuli, as were protoscolices from naturally infected horse and sheep. Stimulation was not detectably reduced by maintenance of the parasite in vitro for 72 h at 37 degrees C or for 46 days at 4 degrees C prior to culture. It is concluded that unprimed lymphocytes are stimulated to transform by surface contact with a stimulator synthesized, but not secreted, by the parasite. The biological significance of the reaction and its possible contribution to immunosuppression are discussed.