Date of Award

8-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biological Sciences

Advisor

Dr. Tom Scott

Committee Member

Dr. Charles Rice

Committee Member

Dr. Charlie Wei

Committee Member

Dr. Jeremy Tzeng

Abstract

Thrombocytes are the most abundant circulating cells next to red blood cells in avian blood. Avian thrombocytes are homologous in function to mammalian platelets. Avian thrombocytes and the mammalian platelet are widely recognized contributors to inflammatory responses upon stimulation with various microbial stimulants. However, some observed responses of the avian thrombocyte depart from a standardized model ascribed to innate cells. To help unravel the role of thrombocytes in innate immunity, and possibly adaptive immunity, first we examined the surface features of chicken thrombocytes. Chicken thrombocytes constitutively express transcripts for different Toll-like receptors (TLRs) that are crucial for the innate immune response. We observed surface expression of major histocompatibility complex II, which is exclusively limited to true antigen presenting cells (APC). Furthermore, we have also detected surface expression of co-stimulatory molecules CD40, 80 and 86 on chicken thrombocytes. Expression of MHC II and co-stimulatory molecules indicates that thrombocytes are unconventional/unique immune cells that not only resemble innate effector cells in function but may have a role in affecting adaptive immunity through cellular contact and interaction with APC and lymphocytes. Next, we examined inflammatory responses when thrombocytes were stimulated in vitro and in vivo with several TLR ligands and vaccines, respectively. In vitro treatment of thrombocytes with various TLR ligands demonstrates a definite bacterial effect while no viral effect on gene expression of IL-6. Bacterial ligand, LPS stimulation led to release of significant amounts of active IL-6 in the thrombocyte culture supernatants. The in vitro treatment of thrombocytes also indicated constitutive expression of iNOS gene expression. Although in vitro treatment of thrombocytes with viral TLR ligands induced significant release of nitric oxide (NO) into culture supernatant, bacterial TLR ligands did not lead to release of NO. In vivo treatment by vaccination with the recommended doses was not sufficient to stimulate chicken thrombocytes to induce expression of pro-inflammatory mediators. Understanding how TLRs initiate particular thrombocytic responses and the involvement of thrombocytes in antigen presentation may shed new light on adjuvant and vaccine research for vaccine development for different poultry diseases.

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