HOW CUSHING'S DISEASE AFFECTS IMMUNITY
(from Equus issue 457 October 2015 page 12)
There is new research from Oklahoma State University suggests that horses with PPID/Cushing's disease can be more susceptible to infection. "Neutrophils migrate to areas of infection or inflammation in a process called chemotaxis. To exit the blood vessels, neutrophils first stick onto the vessel walls, a process known as adhesion. Without adhesion and chemotaxis the neutrophils can't get to the site of infection or inflammation," explains Dianne McFarlane, DVM, PhD. Once they arrive at an area of inflammation, neutrophils can engulf foreign or necrotic material including bacteria - a process called phagocytosis. They are able to kill bacteria by releasing enzymes and chemicals, a process known as oxidative burst. Together, these four actions of neutrophils are necessary for a robust immune system."
McFarlane and her team discovered that horses with PPID had significantly reduced oxidative burst activity and adhesion than did healthy horses. None of the study horses had active infections, and the reduction in these functions was not correlated to severity of PPID. McFarlane says this study underscores the importance of managing PPID horses with medication to balance their hormone concentrations and avoid secondary infections. "In older horses with infections that are not responding well to treatment, it is important to determine their PPID status," she says.