Title page for ETD etd-07312007-185052


Type of Document Dissertation
Author MacKinnon, Kathryn Michelle
Author's Email Address kmackinn@vt.edu
URN etd-07312007-185052
Title Differential gene expression and immune regulatory mechanisms in parasite-resistant hair and susceptible wool sheep infected with the parasitic nematode, Haemonchus contortus
Degree PhD
Department Genetics
Advisory Committee
Advisor Name Title
Notter, David R. Committee Chair
Elgert, Klaus D. Committee Member
Laubenbacher, Reinhard C. Committee Member
Wong, Eric A. Committee Member
Zajac, Anne M. Committee Member
Keywords
  • Immune effector
  • Microarray
  • TH2 response
  • RT-PCR
Date of Defense 2007-07-23
Availability unrestricted
Abstract
Among sheep producers, the parasitic nematode Haemonchus contortus is a major animal

health concern. Caribbean hair sheep are more resistant than conventional wool breeds to this

blood-feeding, abomasal parasite. Our objective was to determine differences in the immune

response associated with parasite-resistant hair and susceptible wool lambs infected with 10,000

H. contortus and in uninfected controls. Animals were sacrificed and abomasum and lymph node tissues were collected at 3 or 27 days post-infection (PI), and for controls on day 17, 27, or 38 relative to d 0 of infected animals. Blood and fecal samples were collected throughout the

study.

Lower fecal egg counts, higher packed cell volumes, and heavier lymph nodes of infected

hair compared to wool lambs, suggests hair lambs have increased parasite resistance. Greater

tissue infiltration of eosinophils (P < 0.05) was observed in hair compared to wool sheep by 3

days PI, with no breed differences in globule leukocytes. Total serum IgA and IgE were greater

in control hair versus wool sheep (P < 0.05). After 3, 5, and 21 of infection, total serum IgA (P< 0.05), total lymph node IgE (P < 0.01), but not total serum IgE were greater in hair sheep

compared to wool sheep.

Gene expression was measured between hair and wool lambs for abomasal and lymph

node tissues using bovine cDNA microarrays and real-time RT-PCR. Microarray analysis

revealed cell survival, endosome function, gut motility, and anti-coagulation pathways are

important in abomasal and lymph node tissues during H. contortus infection. Immune genes,

including IL-4, IL-4 Ra, IL-12 Rb1, and IL-12 Rb2, are also highly represented in abomasal or

lymph node tissue of infected animals. Eleven genes were evaluated using real-time RT-PCR

and included TH1 and TH2 cytokines, cytokine receptors, and IgE. Parasite infection leads to

increased expression of IL-13 and IgE in both tissues and breeds when compared to control

animals. Breed comparison of gene expression shows resistant hair sheep produce a stronger

modified TH2-type immune response during infection. Differential cell infiltration, antibody production, and regulation of TH2 cytokines between breeds may be partially responsible for differences in parasite resistance.

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