Date of Award

2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Animal Science

First Advisor

Waldron, Matthew

Abstract

The dairy cow experiences a period of immunosuppression around the time of calving that contributes to the increased incidence and severity of infectious diseases observed during this period. This reduction in immune capacity is due in part to the impairment of neutrophil function, a key component of the innate immune system. In fact, the success of the host defense mechanisms against infection depends on the ability of neutrophils to reach the site of the infection, recognize, engulf and ultimately destroy the pathogen using several mechanisms such as the generation and release of reactive oxygen species (ROS) and the recently described neutrophil extracellular traps or NETs. The alteration in some of these functions and the overall killing ability of neutrophils during the periparturient period has been widely described. However, the physiological mechanisms underlying the period of immunosuppression are not completely elucidated. Interestingly, the impairment of these immune defense mechanisms coincides with the profound metabolic changes associated with parturition and lactogenesis. Changes in several hormones and metabolites have been proposed to be the cause of the reduction in neutrophil function, but the effect of insulin on the functional capacity of these cells has not been investigated. Not only does the concentration of plasma insulin fall as parturition approaches, but also the animal experiences a period of impaired insulin action, termed insulin resistance, during this same time-frame. Therefore, we isolated circulating neutrophils from periparturient and midlactating cows and incubated them with insulin alone or in combination with the insulin-sensitizing agent 2,4- thiazolidinedione (TZD). Subsequently, we measured the total, extracellular, and intracellular generation of ROS, NETs release, phagocytic and killing ability. Insulin did not improve any of the parameters used to assess neutrophil function. In contrast, TZD had a potent inhibitory effect on the total ROS generation, despite an increase in extracellular superoxide anion production. Surprisingly, TZD did not alter the ability of neutrophils to phagocytose and/or kill Staphylococcus aureus during an in vitro coculture. Results suggest that TZD can reduce the oxidative stress that neutrophils experience during their respiratory burst and diminish the damage that ROS cause to the surrounding tissue without compromising the capacity of neutrophils to eliminate the invading pathogen.

Download

Share

COinS