Open Access
Schneider, Rhiannon Marie
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
Committee Members:
  • Avery August, Thesis Advisor
  • Interferon gamma
  • IgG
  • West Nile Virus
  • real time RT PCR
West Nile Virus (WNV) was first identified in the United States in 1999 in several avian species, the natural host and transmitters of the virus. Incidental infection can occur in horses, and , although infections are most often asymptomatic, neurological signs such as ataxia, hind limb paresis and muscle tremors can occur. In severe cases, encephalitis, myelitis or death may occur. Currently, the only significant protection against WNV infection in horses is through vaccination. There are currently seven licensed vaccines on the market to protect horses against WNV infection. The first approved vaccine was an inactivated whole virus product but others include a modified live canarypox-vectored vaccine, a purified DNA plasmid vaccine, and several combination vaccines using both the whole killed and modified live viral products. Combination vaccines have been made to protect horses from WNV and eastern/western encephalomyelitis, Venezuelan encephalomyelitis, and/or tetanus toxoid. Much of the current research on equine immunity to WNV infection demonstrated that antibody was protective against infection. Interestingly research has also shown that horses have more IgG isotypes than most other species which suggests that isotype variation may be important for an effective immune response in the horse. Other studies showed that specific IgG subtypes should be targeted in the production of specific vaccines to maximize effector function. However, there was a paucity of data to define the specific subtypes responsible for protection afforded by many of the current vaccines. Also, little research has been conducted in horses to define specific cellular immune responses elicited in response to vaccination against WNV. There is a strong need to evaluate the current vaccines for efficacy so that future vaccines may be optimized to afford greater protection against WNV infection of horses with more effective vaccine protocols. The aim of this study was to evaluate both the humoral and cellular immune responses elicited in Quarter Horse foals vaccinated with either the killed or modified live vectored vaccine with specific emphasis on T-cell activation and antibody subtype production. Our results suggested that the killed vaccine produced a significantly higher antibody response in foals compared to the modified live vaccine for each subtype tested with the IgG(T) subtype having the highest titer followed by IgG(b) and IgG(a). An assay for analysis of T- cell activation measured by interferon gamma production from peripheral blood lymphocytes in WNV-vaccinated foals was validated in this study. Lymphocytes were isolated either by direct lysis of red blood cells or by ficoll gradient separation, and interferon gamma measured by RT-PCR. Phenotyping results of the peripheral blood lymphocytes showed comparable retention of T lymphocyte populations using either method of isolation. Further research is needed to identify specific differences that may exist between the stimulation of the immune system. This research will benefit further investigations of immune activation following vaccination of horses for West Nile Virus infection and contribute to ongoing studies of the analysis of vaccine efficacy.