Changes in the flow and composition of gastric lymph in sheep repeatedly infected with Ostertagia circumcincta

Efferent intestinal lymph protein responses in nematode-resistant, -resilient and -susceptible lambs under challenge with Trichostrongylus colubriformis

The mechanisms underlying resistance to challenge by gastrointestinal nematode parasites in sheep are complex. Using DIGE, we profiled ovine lymph proteins in lambs with host resistance (R), resilience (Ri) or susceptibility (S) to a daily trickle challenge with the nematode Trichostrongylus colubriformis. Efferent intestinal lymph was collected prior to infection (day 1) and on days 5 and 10 post-infection. Eight proteins identified by LC-MS/MS, showed differences relating to host genotype. Of these, Serpin A3-3 and Serpin A3-7 have not been reported previously in the lymph proteome. Three acute phase proteins showed significant differences relating to interactions between breeding line and parasite challenge, including complement C3β, C3α and haptoglobin (Hp) β. In the R lambs C3α was significantly up regulated (P<0.05) on day 10, while in the Ri lambs Hp β was significantly down regulated (P<0.05). In the S lambs, levels of C3β were up regulated and levels of Hp β down regulated (both P<0.05) on day 10. Hence we demonstrate that acute phase inflammation proteins contribute to differences in the innate immune response of sheep to challenge by T. colubriformis. The findings may lead to the development of new approaches to combat nematode infestations in sheep production systems.

BIOLOGICAL SIGNIFICANCE

Breeding lines of sheep with resistance (R), resilience (Ri) or susceptibility (S) to nematode infections provide an experimental model to examine the biological mechanisms underlying the ability of some sheep to expel worms and remain healthy without the use of an anthelmintic. Using proteomics we identified differences in the expression of acute phase lymph proteins in the R, Ri and S lambs. The results will assist the development of alternative control strategies to manage nematode infections in livestock.

Kinetics of the local immune response in the gastric lymph of lambs after primary and challenge infection with Teladorsagia circumcincta

Groups of 5-month-old lambs which had been trickle infected with Teladorsagia circumcincta for 8 weeks then drenched, and worm-free control lambs were challenged with 50 000 T. circumcincta L3s. From 10 days later fewer parasites were recovered from the previously infected sheep, and secondary cellular and humoral responses were observed in the gastric lymph. Increases in CD4+ and CD25+ T lymphoblast traffic on day 3, followed by CD21+ and IgA+ lymphoblasts on day 5, and an increase in total and parasite specific IgA concentrations peaking on day 6 were observed in previously infected lambs. Similar peaks in lymphoblast output were not observed until days 10-12 in the control lambs. This data was highly comparable with that obtained recently from yearling sheep subjected to an identical infection-challenge regime, and contrasted with that obtained from similar experiments in the 1980s when 4(1/2)-month-old previously infected lambs were more susceptible to and had much weaker immune responses to challenge than 10-month-old sheep. The fact that 40% fewer larvae were given during the trickle infection regime in the four recent trials is offered as an explanation for this difference.

Kinetics of the local cellular response in the gastric lymph of immune and susceptible sheep to infection with Teladorsagia circumcincta

Groups of yearling sheep were trickle infected with Teladorsagia circumcincta for 8 weeks, then the infection cleared with anthelmintic and both these animals and a group of parasite naïve sheep were challenged with 50 000 infective T. circumcincta larvae. The previously infected sheep demonstrated acquired immunity to the parasite, manifested by reduced worm burdens which were evident as early as 2 days after challenge. Cannulation of the common efferent gastric lymph duct allowed the kinetics of their local cell traffic to be monitored, and the phenotype of these lymphocytes was analysed. A blast cell response, consisting of both T and B lymphocytes, was observed in both groups of sheep, however this occurred more rapidly in the previously infected, immune animals. CD4+, CD8+ and CD25+ blast cell output peaked at day 3 in the previously infected animals, whereas CD21+ blast cell output peaked slightly later at day 5. In the control group the peak output of all phenotypes of blast cells occurred more slowly, peaking 10 days after infection.

The proteome of gastric lymph in normal and nematode infected sheep

Lymph node cannulation allows the collection of lymph draining from a defined anatomical region. Proteomic analysis of that lymph offers a potentially valuable insight into the immunoinflammatory response of that particular region. In this study, ovine gastric lymph has been used to monitor the proteomic changes occurring in the tissue fluid of the abomasum, in response to infection with the parasitic nematode, Teladorsagia circumcincta. Lymph, collected temporally over an experimental infection period, was analysed by means of 2-DE and subsequent gel analysis using densitometry software. In addition, the composition of the lymphatic proteome was further explored by means of MALDI-TOF and MS/MS analyses. The concentration of gelsolin, alpha-1 beta glycoprotein and haemopexin were altered significantly (p<0.05) with infection.

Parasite loss and inhibited development of Teladorsagia circumcincta in relation to the kinetics of the local IgA response in sheep

Groups of yearling sheep, which had been trickle infected with Teladorsagia circumcincta for 8 weeks and then drenched, were challenged with 50 000 T. circumcincta larvae together with groups of worm-free controls. Fewer parasites and a greater proportion of early fourth stage larvae were recovered from previously infected sheep compared to controls. Worm loss and arrested development were evident by 5 days after challenge whereas growth retardation of developing worms was observed by day 10. In the previously infected sheep a secondary IgA response was observed in the efferent gastric lymph from 5 days post-infection. Western blot analysis showed the lymph IgA to be predominantly dimeric and nonsecretory in nature and that the somatic antigens recognized were predominantly in the 100-250 kDa range. The concentration of IgA in lymph was always higher than in blood and in the previously infected sheep increased fivefold 8 days post-challenge in contrast to blood where IgA levels were unchanged. The timing of the response suggested that it occurred too late to have been the cause of worm loss or arrested development, though it may have retarded the growth of developing parasites.

An immunogenic cathepsin F secreted by the parasitic stages of Teladorsagia circumcincta

Teladorsagia circumcincta is a common, pathogenic abomasal nematode of sheep. In order to improve disease control in parasite isolates resistant to several anthelmintics, alternative methods must be sought. Sheep develop acquired immunity to T. circumcincta so vaccination is a valid option for control. For this reason, we are investigating parasite excretory/secretory products for molecules, which have potential to invoke protective immunity against T. circumcincta. Here, we describe experiments in which we identified a novel, immunogenic cathepsin F secreted by L4 T. circumcincta. This protease, initially identified by mass spectrometry analysis, is the most abundant molecule in excretory/secretory products released in vitro by T. circumcincta harvested at 5, 6 or 9 days p.i. and is a target of specific, local IgA responses in sheep which are immune to challenge infection. The full-length cDNA encoding this secreted protease was isolated. Sequence and phylogenetic analyses indicated that the protease (designated T. circumcincta cathepsin F-1, Tci-CF-1) belongs to the cathepsin F class and exhibits greatest identity (>60%) to expressed sequence tags present in the Ostertagia ostertagi and Haemonchus contortus expressed sequence tag databases. Tci-CF-1 also displays high identity to hypothetical proteins identified in the genomes of Caenorhabditis elegans and Caenorhabditis briggsae, both proteins having been described as cathepsin F enzymes. Specific inhibitor binding assay of larval excretory/secretory products confirmed the classification of this excretory/secretory component as a cathepsin F. Reverse transcription-PCR studies indicated that Tci-cf-1 is developmentally regulated and is particular to the host parasitic stages of T. circumcincta. The abundance, immunogenicity and temporal expression pattern of Tci-CF-1 make this a potential vaccine candidate for teladorsagiosis.

Long-term collection and characterization of afferent lymph from the ovine small intestine

Reliable methods for long-term collection of afferent lymph draining from the small intestine of sheep are described and validated. The procedure was used successfully in normal sheep, in animals infected experimentally with the parasitic intestinal nematode Trichostrongylus colubriformis and in animals infected naturally with Mycobacterium avium subsp. paratuberculosis, the causative agent of Johne's disease. Our approach enabled afferent lymph draining from the small intestine to be collected continuously for up to 4 months, without any detrimental effects on the animals. Based on cytokine gene expression profiles of afferent intestinal lymph cells, the two infections induced contrasting regional immune responses, namely, Th2-type immunity in the case of T. colubriformis infection and Th1-type immunity in natural cases of Johne's disease. Some immune parameters differed markedly between the two disease models, highlighting the potential value of this approach to gain real-time insights into distinctive host-pathogen interactions as they occur in vivo within the regional immune system of the gastrointestinal tract.

Nutrient partitioning between reproductive and immune functions in animals

The physiological processes that underlie the reproductive cycle impose considerable metabolisable protein (MP) demands on a female, especially during the periparturient period. When MP supply falls short of MP demand (i.e. MP becomes scarce), certain, if not all, bodily functions are expected to be penalised. It has been proposed that partitioning of scarce MP is prioritised to reproductive rather than to immune functions. In other words, at times of MP scarcity, the penalty on expression of immunity would be expected to be greater than that on reproduction. This hypothesis forms a nutritional basis for the occurrence of periparturient breakdown of immunity to parasites (BIP), which can be observed in many host-parasite systems. In the present review we explore this nutritional basis, using periparturient sheep infected with the abomasal nematode Teladorsagia circumcincta as an example, and attempt to quantify its occurrence. Evidence supporting the nutritional basis of periparturient BIP is reviewed, covering experiments in which nutrient supply (from both exogenous and endogenous sources) and/or nutrient demand were manipulated. Quantitatively, MP requirements for expression of immunity to T. circumcincta were estimated to be about 1 g/kg metabolic body weight (body weight 0.75) per d, approximately 5% of the maximum MP requirements of periparturient sheep. The major component of this requirement was assumed to be for replenishing irreversible plasma protein losses into the gastrointestinal tract. Although confirmation of this estimate is required, such estimates may be used to improve the known MP requirements of periparturient animals, enabling the extent and the consequences of periparturient BIP to be minimised.

IgE antibody during infection with the ovine abomasal nematode, Teladorsagia circumcincta: primary and secondary responses in serum and gastric lymph of sheep

A monoclonal antibody to ovine IgE was employed in an ELISA to investigate the IgE antibody responses in serum and gastric lymph to a primary infection of Teladorsagia circumcincta, and following challenge in previously infected sheep. During a primary response, IgE antibody to antigens derived from the infective third stage (L3) and adult (L5) worms were negligible, with low levels of IgE antibody detected in serum and lymph. In contrast, there was a pronounced IgE antibody response in 2/4 sheep to L3 antigens during 2-8 days after challenge of previously infected animals but low levels of IgE antibody to L5 antigens. This response was confirmed in a second but similar experiment, where relatively high levels of IgE antibody was detected to antigens from L3. Antibody levels were higher in lymph than in serum from the same animals, and Western blots of L3 antigen following SDS-PAGE under reducing conditions revealed several bands of MW26-96KD which reacted with the IgE antibody from gastric lymph. Immunohistochemical staining indicated that these IgE antibodies may be reacting with allergens associated with the surface cuticle of the worms.

IgE responses in the serum and gastric lymph of sheep infected with Teladorsagia circumcincta

The IgE response of naive or previously infected sheep to 50,000 infective larvae of Teladorsagia circumcincta was monitored in serum and gastric lymph using a monoclonal antibody generated to recombinant ovine IgE in a dot blot assay. In 4/5 naive sheep, lymph and serum IgE concentrations increased from days 8 and 14 after infection, respectively. In most previously infected sheep, the IgE response to challenge was more rapid, although not necessarily greater than that following a primary infection. IgE concentrations in lymph were some 4-fold higher than in serum indicating that its source was the mucosa or draining nodes.

Local eosinophil- and mast cell-related responses in abomasal nematode infections of lambs

Eosinophil numbers in peripheral blood and eosinophil potentiating activity (EPA) and sheep mast cell protease (SMCP) in efferent gastric lymph were monitored in lambs during infections with Ostertagia circumcincta. Worm burdens, eosinophil numbers in bone marrow, abomasal mucosa and gastric lymph node, as well as mast cell numbers and SMCP concentrations in mucosa and mucus, were determined in post mortem samples. In naive lambs, high and relatively uniform worm burdens were present 10 days after primary infection and these were associated with only mild blood and tissue eosinophilia. By day 21 worm burdens were markedly lower and more variable. There was more evidence of eosinophil and mast cell accumulation in mucosa, and numbers in bone marrow were also higher than on day 10. However, neither EPA nor SMCP were detectable in lymph. By contrast, EPA and SMCP were present in substantial amounts in draining lymph within 48 h of challenge (secondary) infection of previously exposed lambs. EPA was inversely related to worm burdens recovered on day 10, as were abomasal mucosal and mucus SMCP concentrations. Elevated eosinophil numbers were also consistently detected in blood, bone marrow, mucosa and gastric lymph node. The results suggest that host immune defence against secondary, but not primary, exposure to O. circumcincta involves a rapidly mobilised local inflammatory component.

Sequential histopathologic changes of type I, pre-type II and type II ostertagiasis in cattle

Yearling cattle in Louisiana were examined at monthly intervals for abomasal nematode burdens and histological lesions over a year. Tracer calves were grazed for 3 to 4 weeks and removed from pasture for 2 to 3 weeks, then slaughtered; a few animals were killed in extremis shortly after removal from pasture. Histological changes were correlated with worm burdens and characterized according to the type of Ostertagia ostertagi infection present. In cattle with acute Type I ostertagiasis, changes varied from eosinophil infiltration to glandular dilation and slight mucous cell hyperplasia with submucosal edema. During the summer months the cattle had worm burdens that were primarily early 4th stage larvae (EL4), with changes characterized by minimal glandular dilation and mucous cell metaplasia and moderate lymphoid cell proliferation and with intramucosal migration of EL4. In the autumn, the maturation of EL4 produced the Type II syndrome with severe glandular changes, prominent mucosal hyperplasia and marked lymphoid cell accumulation. With increased duration of the pre-Type II interval, there was greater development of the subepithelial lymphoid tissue and increased frequency of epithelial globule leukocytes. The lymphoproliferation which occurred during the prolonged pre-Type II interval appeared to be related to the increased severity and mortality seen with the Type II ostertagiasis syndrome.

Systemic release of a mast cell proteinase following nematode infections in sheep

An enzyme-linked immunosorbent assay (ELISA) for sheep mast cell proteinase (SMCP) has been developed. Concentrations of SMCP in homogenates of abomasal tissue from parasite-immune sheep (341 micrograms SMCP/g tissues) were raised when compared to those in normal (non-infected) abomasa (0.145 micrograms SMCP/g tissue). SMCP was not detected in sera from normal animals challenged with Haemonchus contortus but was present (less than 1.0 ng SMCP/ml) in sera from 8/11 immune sheep 2 h after intra-abomasal challenge with 1 x 10(6) exsheathed Haemonchus larvae. In two further experiments, the SMCP response in gastric lymph was monitored after homologous larval challenge in sheep immune to Ostertagia circumcincta and in normal controls. SMCP (less than 1.4 ng SMCP/ml) was detected in lymph from 2/3 and 4/5 immune animals between 1 and 4 days post-challenge with 50,000 larvae, but not from normal animals. SMCP was not detected in lymph from immune animals following challenge with 1000 Ostertagia larvae. The relatively low concentrations of SMCP in blood and lymph reflect the presence of proteinase inhibitor(s) which interfered with the ELISA.

Effects of Pasteurella haemolytica cytotoxin on ovine peripheral blood leucocytes and lymphocytes obtained from gastric lymph

Ovine peripheral blood leucocytes were separated on discontinuous Percoll density gradients into fractions rich in lymphocytes (PBLy) and polymorphonuclear leucocytes. Supernatant fluid from a dialysis sac culture of Pasteurella haemolytica biotype A serotype 1 (A1) was cytotoxic to these leucocytes in vitro. PBLy retained viability after storage in liquid nitrogen and could be employed in cytotoxicity assays. However, sheep cannulated via the common gastric lymph duct were an excellent source of large numbers of homogeneous lymphoid cells (GLy) which also stored well in liquid nitrogen. As both freshly collected and stored GLy were killed by culture supernatant fluid GLy offer advantages as target cells for further characterisation of the extracellular cytotoxin produced by P. haemolytica. From the results obtained, it is considered that all ovine leucocytes are susceptible to P. haemolytica cytotoxin.

Age immunity to Ostertagia circumcincta: comparison of the local immune responses of 4 1/2- and 10-month-old lambs

In 2 experiments, the local immune response to infection with 50,000 O. circumcincta was monitored in 4 1/2-month-old previously infected lambs by following changes in the composition of gastric lymph. The previously infected lambs were partially resistant to the challenge in that they harboured a greater proportion of early fourth stage parasites and that the developing larvae recovered from them were distinctly shorter than those present in controls. They also exhibited a secondary local immune response in the gastric lymph consisting of increases in the output of lymphoblasts and IgA cells which peaked 3 to 5 days after challenge, followed by increases in lymph IgA and IgA anti-larval antibody on days 6 and 7. The size of the total IgA response in a sheep was highly correlated with the degree of stunting of its larvae, suggesting that IgA antibody can reduce the growth of developing Ostertagia. When compared with the results of 2 identically designed experiments carried out previously in 10-month-old sheep, the younger lambs were measurably less resistant to challenge and most aspects of the magnitude of the local immune response were significantly depressed, although the timing of the response was similar. It is suggested that this poorly developed ability to mount a secondary mucosal immune response may explain the relative failure of the younger lamb to develop resistance to gastro-intestinal nematodes.

Manifestations of resistance to ovine ostertagiasis associated with immunological responses in the gastric lymph

Groups of previously infected and worm-free sheep were serially killed up to 10 days after challenge with 50 000 Ostertagia circumcincta larvae. Two similar groups of sheep were killed 10 days after challenge with 1000 larvae. The previously infected sheep were resistant to the smaller challenge dose in that fewer, stunted worms were recovered from them than from controls. However, this resistance was not as marked as that observed in the previously infected sheep which received the large challenge, because proportionally fewer worms were recovered after the 50000 dose and the great majority of these were arrested at the early fourth stage. The gastric lymph ducts of 6 previously infected sheep were cannulated successfully and a marked local immune response was detected in 3 sheep which were challenged with 50 000 larvae. No response was detected in 3 cannulated sheep challenged with 1000 larvae. In the lymph of the 50 000 dose group, a temporary increase in pepsinogen activity suggested that a hypersensitivity reaction related to the presence of large numbers of mucosal mast cells began between 24 and 48 h after challenge. This was followed by marked increases in the cellular and IgA content of lymph, which reached peaks on days 3 and 6, respectively. It is suggested that the response detected in the gastric lymph reflected aspects of a local immune reaction in the abomasal mucosa and that this reaction accounted for the enhanced degree of resistance to the larger challenge dose.

Local immunity and Ostertagia circumcincta: changes in the gastric lymph of sheep after a primary infection

Some aspects of the kinetics of the primary local immune response to O. circumcincta were studied by monitoring the flow and composition of gastric lymph from 4 sheep for 3 weeks after infection with 50 000 larvae. A significant increase in the frequency of lymphoblasts in the lymph showed that all the sheep were responding immunologically to the parasites from day 8 onwards. However, considerable individual variation in degree and timing was evident in other aspects of the immune response; 2 animals responded with large increases in lymphocyte output which reached a peak on day 5 or day 10, whereas the main response in the other 2 sheep appeared to be inflammatory in nature, with large increases in lymph flow and eosinophil output which occurred during the third week of infection. No significant changes in the content of IgA or IgA anti-worm antibody were detected in the lymph, but pepsinogen concentrations were significantly raised from day 12 onwards.

Studies on the local immune response of the lactating ewe infected with Ostertagia circumcincta

Changes in the flow and composition of gastric lymph were monitored in groups of lactating and non-lactating ewes which were repeatedly infected with Ostertagia circumcincta. As judged by faecal egg counts and worm burdens the lactating group was more susceptible than the non-lactating controls to the challenge infection. Increased amounts of pepsinogen as well as larger numbers of eosinophils and neutrophils entering the gastric lymph indicated considerable abomasal damage and inflammation in the lactating ewes. However, measurement of the flow of lymphocytes as well as the amount of IgA and IgA antibody in the lymph did not indicate that these aspects of the local immune response were impaired during lactation; in fact the output of IgA-containing lymphocytes as well as IgA itself was usually raised in the lactating sheep. Lymph flow was increased and lymph globulin concentrations proportionally decreased in lactating ewes, irrespectively of whether they were infected with worms. It is suggested that these changes were caused by the increase in voluntary food intake which occurs during lactation.