COMPARATIVE INVESTIGATION OF THE IMMUNE SYSTEMS OF TWO OVINE SPECIES (OVIS ARIES AND OVIS CANADENSIS)

Margaret Ann Highland

Chapter 1 describes the economic and ecologic significance of respiratory disease in domestic sheep (DS; Ovis aries) and bighorn sheep (BHS; Ovis canadensis) and the need for interspecies comparative immune analyses. In order to identify inherent immune differences, possible confounding factors in immune analyses need to be minimized, including age, exposure history (immune status), and environmental stressors. Therefore, the studies described herein were performed on hand-raised DS and BHS lambs, raised to adulthood, maintained under similar environmental conditions. Hand-raising DS and BHS lambs allowed for interspecies comparative evaluation of maternal passive transfer of total IgG, reported in Chapter 2. This research revealed no significant interspecies differences for total IgG concentrations in ewe sera, colostrum, or lamb sera at 1 day through 12 weeks of age, and no significant difference in apparent efficiency of absorption were identified. Maternal IgG waned similarly over time in DS and BHS, with the nidus at 6 weeks of age. Chapter 3 describes a set of cross-reactive monoclonal antibody reagents valuable in comparative immune system analyses of these two ovine species. Interspecies comparative analyses performed on neutrophils and ConA stimulated lymphocytes revealed interspecies differences in abundances of molecules that play critical roles in host responses to bacterial infection, including 2 integrin subunits, CD18, CD11a, and CD11b; the pathogen recognition receptor for lipopolysaccharide, CD14; an inflammation regulatory protein, CD172a; and a subunit of the receptor for IL-2, CD25. This study provides novel base data and insight for further elucidating immune system differences in DS and BHS. Chapter 4 describes interspecies in vitro comparative analyses of responsiveness of DS and BHS neutrophils to two bacteria identified in association with ovine pneumonia, Mannheimia haemolytica (Mh) and Fusobacterium necrophorum (Fn), and the exotoxin that each secretes. Analyses include cytotoxicity, cytotoxicity neutralization, and bacterial proliferation inhibition assays. While more susceptible to the cytotoxic effects of both Mh and Fn exotoxins, BHS neutrophils are similarly capable of controlling Mh proliferation, provided similar in vitro immune conditions. Our results also indicate an importance for both humoral immunity (antibody) and complement in controlling Mh proliferation.

COMPARATIVE INVESTIGATION OF THE IMMUNE SYSTEMS OF TWO OVINE SPECIES (OVIS ARIES AND OVIS CANADENSIS)

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