Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Patricia Ann Melrose


Stress has been related to increased plasma epinephrine (E), norepinephrine (NE), and glucocorticoids. These compounds produce immunomodulatory effects by interacting with hormone receptors on or in various immune cells. This project assessed the effects of stress on equine influenza virus (EIV)-specific and mitogen-induced lymphoproliferation of peripheral blood mononuclear cells (PBMCs) in relation to stress-induced changes in E, NE, and cortisol. In vitro effects of amines on proliferative responses and glucocorticoid receptor (GR) assays were done as a secondary measure of hormone and neurotransmitter interactions with the immune system. Time-dependent, saturable-specific hormone binding to GRs was abolished by heat treatment and subcellular localization of GR fluctuated in a diurnal manner. Nuclear GR was lowest (P $<$ 0.05) at 2AM and total binding was highest (P $<$ 0.05) at 2PM. In experiment two, horses were subjected to five different stress tests including sham/stalled (SS), sham/psychological (SP), minimal exercise stress (MES), slow gallop/moderate exercise stress (SG), and fast gallop/intense exercise stress (FG). Circulating concentrations of E increased in SG and FG. Influenza-specific blastogenesis increased (P $<$ 0.05) during the sham/stalled stress test. Mitogen-induced lymphoproliferative responses were lower (P $<$ 0.05) for samples collected during MES. There was no correlation between stress-induced hormone concentrations and lymphoproliferative responses. Norepinephrine stimulated (P $<$ 0.05) mitogen-induced lymphoproliferation in vitro. EIV-specific lymphoproliferation was not affected by E or NE. Isoproterenol stimulated mitogen-induced lymphoproliferation. Thus, $\beta$-adrenergic receptors may be related to stimulatory effects of NE. Ponies were subjected to SS, MES, SG, and FG. Circulating cortisol concentrations decreased (P $<$ 0.05) during SG and FG. Lymphoproliferation did not change relative to stress. Prior history of the ponies and measurable cortisol concentrations suggested that long-term effects of rearing processes are important to the stress response in adult animals. Results from this study suggest that stress-dependent changes in E, NE, and glucocorticoid concentrations are unlikely to be primary mediators for stress-induced changes in lymphoproliferative responses. Other putative factors or a combination of hormones and amines may be involved in stress-induced modulation of lymphoproliferation.