Differential gene expression and immune regulatory mechanisms in parasite-resistant hair and susceptible wool sheep infected with the parasitic nematode, Haemonchus contortus

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.