Date of Graduation


Document Type


Degree Type



Davis College of Agriculture, Natural Resources and Design


Animal and Nutritional Sciences

Committee Chair

Scott A Bowdridge

Committee Co-Chair

Vagner A Benedito

Committee Member

Christopher F Cuff

Committee Member

Robert L Taylor

Committee Member

Anne M Zajac


Parasitism by Haemonchus contortus is the greatest concern of sheep producers and results in billions of dollars in economic loss each year. St. Croix hair sheep are naturally resistant to H. contortus infection, but have body characteristics which are unfavorable for production. Resistance to H. contortus is immune mediated; characterized by a T helper type 2 (Th2) response, however the mechanism of the development of immune response is not known. In these studies, immunological responses of parasite resistant St. Croix sheep and Suffolk sheep peripheral blood mononuclear cells (PBMC) are evaluated in response to H. contortus antigens. Three uninfected H. contortus primed St. Croix sheep and three uninfected H. contortus primed Suffolk sheep were used to collect PBMC. PBMC were cultured in vitro with H. contortus crude larval antigen (CLA) or crude worm antigen (CWA) for varying amounts of time. Cell culture supernatants were collected for cytokine evaluation by ELISA and RNA was extracted from cells for analysis by qPCR or RNA-Sequencing. Cytokine ELISA revealed PBMC from St. Croix produce greater amounts of interleukin-4 (IL-4), the characteristic cytokine required for and produced by Th2 cells, then Suffolk PBMC exposed to CLA. St. Croix sheep generated appreciable IL-4 by 6 hours of culture with CLA, while Suffolk PBMC did not generate IL-4 until 72 hours of culture with CLA. Analysis by qPCR showed St. Croix PBMC upregulated mRNA for the IL-4 receptor (IL4Ralpha), and other key Th2 genes IL-13, IL-5 and MRC1 after 6 hours of culture with CLA. Suffolk PBMC showed downregulated IL4Ralpha and no upregulation of Th2 genes at 6 hours of culture with CLA. RNA-Sequencing revealed St. Croix PBMC upregulate 499 genes in response to 6 hour of culture with CLA, while 130 genes were upregulated in Suffolk PBMC. Increases in genes associated with inflammation, antigen recognition, immune response and function in antigen presenting cells may contribute to the ability of St. Croix to resistance infection by H. contortus.