Studies on the immunity of sheep to Haemonchus contortus (Rudolphi, 1803)

Riffkin, George Gerald (1979). Studies on the immunity of sheep to Haemonchus contortus (Rudolphi, 1803) PhD Thesis, School, Centre or Institute, The University of Queensland. doi:10.14264/uql.2014.484

       
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Author Riffkin, George Gerald
Thesis Title Studies on the immunity of sheep to Haemonchus contortus (Rudolphi, 1803)
Formatted title
Studies on the immunity of sheep to Haemonchus contortus (Rudolphi, 1803)
School, Centre or Institute School, Centre or Institute
Institution The University of Queensland
DOI 10.14264/uql.2014.484
Publication date 1979-01-01
Thesis type PhD Thesis
Supervisor C. Dobson
Total pages 359
Language eng
Subjects 070708 Veterinary Parasitology
Formatted abstract
The optimal conditions for in vitro culture of sheep peripheral-blood lymphocytes were defined and lymphocyte blastogenic responses were determined for cultures containing different concentrations of Phytohaemagglutinin, Concanavalin A, larval and adult Haemonchus contortus antigens by measuring the uptake of tritiated thymidine into stimulated cultures. These responses were measured by liquid scintillation spectrophotometry and taken to be in vitro correlates of the cell-mediated immune response of the sheep to these mitogens. Batches of H. contortus antigens varied in their ability to stimulate blastogenesis in sheep peripheral-blood cultures but reconstituted lyophilised antigens retained their blastogenic properties better than antigens which had been frozen and thawed several times. Fractions of H. contortus antigens separated by gel filtration or ion-exchange chromatography did not stimulate peripheral-blood lymphocyte culture responses as strongly as the unfractionated antigens.

Haemonchus contortus antigen-induced in vitro peripheral blood lymphocyte stimulation indices (PBSI) of sheep infected with H. contortus were greater than those of worm-free sheep. These immunological reactions were largely antigen-specific and were dose dependent. In contrast, lymphocyte responses of H. contortus-infected sheep to antigens prepared from Angiostrongylus cantonensis, Dirofilaria immitis and Toxocara canis were independent of the antigen dose although the reactions of ovine lymphocytes differed between the various antigens.

Cultures of lymphocytes isolated from peripheral—blood, thoracic duct lymph and lymphoid tissues did not respond as strongly to PHA or H. contortus antigens as did whole-blood cultures.

The kinetics of pathophysiological and immunological responses in sheep to H. contortus were studied during primary, repeat and daily infections. Peripheral-blood lymphocyte stimulation indices fell during the first 2 days after infection with H. contortus but rose to a peak about the time that the infections became patent. Peak in vitro whole-blood culture stimulation indices to both third-stage larval (L3) and Adult (Ad) H. contortus antigens occurred earlier in younger sheep and in the absence of patent female worms in one sheep. Lymphocytes cultured in vitro from infected sheep responded more readily to L3 antigen than Ad antigen before and during the early stages of the infection; this relationship was reversed after 9-12 days. Both L3 and Ad antigen-induced peripheral-blood culture stimulation indices declined when the faecal H. contortus egg count was increasing logarithmically. This indicated that the developing stages of the parasite were more immunogenic than were patent female H. contortus. Circulating lymphocyte numbers were low at birth but rose rapidly to reach peak values in 3 and 6 month old lambs before stabilising at slightly lower than peak levels in older worm-free sheep. Changes in lymphocyte numbers preceded similar changes in mitogen-induced in vitro lymphocyte responses. The decline in haemoglobin concentration which occurred during infection was greatest in 5 month old lambs and was proportional to the number of adult H. contortus present at day 35 when the sheep were slaughtered.

Resistance to infection was greater in sucking lambs than in recently weaned lambs but increased with age in weaned lambs and sheep. Age-related resistance was manifested by decreases in the number of adult H. contortus and in parasite eggs produced, and increases in prepatent period and in arrested larval development. Serum haemagglutinating antibody titres to L3 and Ad antigens did not increase during primary infection. A rise in faecal egg output was detected in parturient ewes and coincided with depression in their mitogen-induced in vitro lymphocyte culture responses.

Antigen-induced stimulation indices of lymphocytes cultured in vitro from lymphoid tissues and thoracic duct lymph obtained from sheep at different intervals during primary H. contortus infections were generally much lower than whole-blood culture responses. Spleen cell stimulation indices paralled those of whole-blood and were greatest in sheep slaughtered 21 days after infection. Thymus cell cultures were unresponsive to PHA or H. contortus antigens. L3 H. contortus antigen-induced stimulation indices of in vitro cell cultures from the abomasal lymph node were elevated during primary infection and indicated a local lymphopoietic response to H. contortus.

Sheep which had elevated preinfection blood culture stimulation indices to L3 antigen (HR sheep) had lower preinfection haemoglobin levels and were more resistant to subsequent infection than sheep which had lower preinfection levels of blood culture responses (LR sheep) and high haemoglobin levels. In addition, HR sheep had a greater eosinophilia and gained less weight during infection than did IiR sheep. The rise in the level of H. contortus-antigen-induced PBSI during infection was greater in older than younger sheep. Sheep with haemoglobin type A were generally among the HR group whereas animals with, haemoglobin types AB or B were in the LR group.

Levels of preinfection L3 antigen-induced PBSI of ewes correlated strongly with those of their lambs and appeared to monitor the inherited levels of resistance to infection. This trait was associated with failure of the parasite to become established and could be discriminated from other immunological factors which impart age immunity.

"Self-cure" occurred in some sheep which had been given repeat pulse infections but changes in whole-blood and lymphoid tissue cell culture stimulation indices were less marked during reinfections than during primary infections. Changes in haemoglobin levels were also minimal in reinfected sheep but the degree of eosinophilia increased during reinfection.

In groups of sheep of uniform age and experience with H. contortus, resistance to single or daily infection, or to challenge with H. contortus was greater in HR than in LR sheep. Haemagglutinating antibody titres in the sera from LR but not HR sheep rose during reinfection. LR sheep harboured more worms from the secondary infections than did HR animals and the elevated antibody titre related more to susceptibility rather than resistance to reinfection. The weight gains of LR sheep during primary, repeat and daily infections were greater than those of HR sheep. Selection of sheep for improved rates of weight gain appears to have been at the expense of their resistance to H. contortus.
Keyword Haemonchus contortus
Sheep -- Diseases
Natural immunity

Document type: Thesis
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