A foal's immune system is known to be weak and immature, but new cell-based research suggests that "immunodeficiency" might be too broad a term to define the disease-fighting capacity of the youngest horses.
The research is overturning old theories about foal immunity, which could lead to improved disease prevention methods and more effective treatments for sick foals, according to Bettina Wagner, DVM, PhD, researcher at the College of Veterinary Medicine at Cornell University in Ithaca.
By studying the activity of certain immune-specific cells, scientists at Cornell have determined that some adaptive immune responses in foals are actually similar to those in adult horses. Furthermore, their responses tend to follow a different cell-based pattern than previously thought, Wagner said.
Immune responses come in large part from several different kinds of "T helper" cells, which scientists call "Th." Each kind of Th cell plays a different role in fighting diseases. For example, in the horse, Th1 cells help fight against infections inside the cells themselves. Th2 cells work to defend the body against bacteria and viruses outside the cells.
Each one of these Th cells produces proteins that work like signals. These proteins, called cytokines, can be measured and counted by scientists to understand how the immune system works in foals and adult horses.
Previously, scientists compared the number of cytokines in foals to the number in adults to determine foal immunity levels. Since cytokine levels were significantly lower in foals than in mature horses, foals were considered to be immunodeficient. But according to Wagner, it's balance, not quantity, that counts when measuring cytokines. When you measure the ratio of one kind of cytokine compared to another, you get a whole new picture of what foal immunity really is, she said.
"Collectively, our data demonstrated that T cells from equine neonates and foals are competent in mounting Th1 (and certain other) responses that are qualitatively similar to those observed in adult horses," she said. This is especially true after five days of age, she added.
However, Th2 responses stay low in foals even up to three months of age, according to her research. This places a previous theory, that foal immune systems primarily relied on Th2 reactions, into serious question, Wagner said.
"Characterizing differences and similarities of adaptive immunity in foals and adult horses is important in assessing appropriate immune responses in healthy foals,” she said. “(It is also helpful) in identifying inappropriate immune regulation in diseased foals and in developing improved or new vaccination strategies for very young horses."
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.