The immune system of newborn calves is functional, but not fully developed. For many years much attention has been paid to adaptive immunity, the branch of the immune response that improves with repeated exposure, and so is responsible for development of “immune memory”. This is the branch we are focused on improving with vaccination.
However, in recent years research focused on the innate immune response has shown that the innate immune response is much more complex than was previously appreciated. “Many cells that are not considered to be ‘immune cells’, such as the epithelial cells that line the mammary gland, urogenital tract, and respiratory tract, have been shown to participate in innate immunity by expressing certain cell surface markers or secreting molecules that can protect the cow against infection directly, or indirectly by activating immune cells,” explains Amelia Woolums, DVM, PhD, Dipl. ACVIM, Dipl. ACVM, University of Georgia.
“This means that there are newly recognized pathways that we may be able to manipulate to improve the resistance of cattle to a variety of infections.”
Because the innate immune response is that part of the immune response that is always “on” and doesn’t take any time to be activated, this means that we might be able to improve the “baseline” or “resting” immune response of cattle. “We might be able to make them more able to resist infection at a moment’s notice by improving or manipulating innate immune functions,” Woolums says.
It has been shown that the innate immune system’s components interact with the adaptive immune system to improve adaptive responses. “If we can find ways to manipulate the innate immune system, we may not only improve the cow’s baseline resistance to infection, but we might also be able to improve the cow’s future resistance to infections by improving immune memory, which is the result of the adaptive immune response,” Woolums notes.
For example, molecules such as defensins and cathelicidins, which are antimicrobial peptides produced by a variety of cells in the body and which are involved in the innate immune response, can sometimes act like adjuvants. “That is, they can improve future responses by the adaptive immune response to infectious agents,” Woolums explains. “Because of this, researchers are working to see if adding certain defensins or cathelicidins to vaccines can improve vaccines.”