Toward this end, scientists have studied the ability of selected cytokines such as interferons and interleukins, as immune modulators administered to cattle whose immune systems are compromised, as a way to help them combat infectious diseases. “What we have learned is that many of these cytokines (or regulatory molecules of the immune system) are highly potent and there can sometimes be a very narrow therapeutic dose range before toxic effects are observed,” Kehrli explains. “We don’t currently have products available that meet this need, but I am confident scientists will eventually find immune restoratives to help compensate for a dysregulated immune system during critical phases of production such as the transition cow.”
Weaning, which can be a source of stress, was also recently shown to be associated with decreased neutrophil function in dairy calves (Hulbert et al, J Dairy Sci 2011;94;2545-2556).
Measuring innate immunity
How do you measure innate immunity? Chris Chase, DVM, PhD, Dipl. ACVM, South Dakota State University, says one of the proteins that can be measured is haptoglobulin, an acute phase protein. “Unfortunately, it is always increased after the fact so it really doesn’t tell you what shape the innate immune response is in,” he says. “Alpha interferon is another protein that is measured, but again it is after the fact.”
Woolums says we can measure the neutrophil count in blood (via a CBC) or milk (with SCC, measuring neutrophils). “Neutrophil counts in these body fluids are widely used as a measure of how well, or not well, the cow is doing in terms of infection/inflammation,” she says.
Recently, researchers looked at whether measurement of innate immune factors such as defensins or cathelicidins could be measured in milk to serve as a surrogate measure of somatic cell count (SCC). “This might eventually be a cow-side test that could improve diagnosis of mastitis,” Woolums notes. “However, we do already have the California Mastitis Test, which is a cow-side test that provides a semi-quantitative measure of SCC.”
Kehrli adds that it is also important to understand that numbers of cells alone is not entirely informative and, in fact, could be highly misleading given there are situations where leukocyte numbers may be high but they are not functional.
If a tissue sample test was available, Kehrli says realistically the tissue would need to be readily accessible and blood comes the closest to fulfilling this criteria. “Secondly, I would argue the diagnostic test needs to be a comprehensive immune capacity panel that takes a snapshot of both the innate and adaptive immune systems, including cellular and non-cellular components of each system.”