Immune system development in foals - DVM
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Immune system development in foals
In Part 1 of this series, an equine research team explains two key immune factors—transfer of proinflammatory cytokines to the foal and the foal's ability to respond to antigens.


DVM360 MAGAZINE


"This type of work is interesting, as we're learning that the importance of colostrum may be beyond the IgG, though perhaps IgG is the essential part," continues Felippe. "But it also tells us that there are other 'goodies' in the colostrum that can be very helpful during early life. Perhaps there is a quantitative correlation. We know the greater the amount of IgG, the better protected the foal is. Maybe more cytokines of one kind may be very beneficial for the foal. And maybe too much of another kind may not be beneficial for the foal. We just don't know. Too much of a good thing sometimes is not as good in immunology."

Another important aspect of this research is that the team questioned whether serum cytokine concentrations in neonates could be used to predict the severity or outcome of septicemia, therefore predicting foal survival.

"A lot of equine neonates get sick in early life, even when there are perhaps still high levels of those cytokines absorbed from the colostrum," Felippe says. "If you're trying to correlate the level of TNF-alpha, which is a prime inflammatory cytokine, with the severity of disease and perhaps death outcome, you need to keep in mind that in some foals that have more or less TNF-alpha, despite their inflammatory process, the level may be high or low because of maternal transfer from the colostrum. That is a major confounding value that can change your ability to use that as a prognostic indicator.

"There were some incoherencies in the findings of cytokine levels in septic neonates and how that correlated to survival outcome," continues Felippe. She says part of the problem probably relates to the fact that these foals, independent of their disease, have different backgrounds—some cytokine concentrations are coming via the colostrum, and others may have come from plasma transfusion, which is another way to transfer immunoglobulins and cytokines to foals.

"The plasma is from adult horses that are healthy, but they carry some cytokines along with them," Felippe says. "So we need to be careful about measuring things that are not necessarily inherent to the foal, or endogenous to the foal, but are being absorbed via the colostrum and may affect our ability to use those parameters as prognostic indicators."

Can foals respond to antigens?

Another critical question is how foals respond to antigens and vaccines.

"The equine neonate is considered immunocompetent at the time of birth because the equine fetus is capable of producing antigen-specific antibodies about day 180 to 200 of gestation when vaccinated in utero," says research associate Rebecca Tallmadge, PhD, and her colleagues at Cornell's Equine Immunology Lab.2

It is also known that because the equine placenta prevents transfer of maternal antibodies during gestation and because of the absence of exposure of the fetus to microorganisms, presuckle foals are born hypogammaglobulinemic and nave to environmental pathogens.2

Humoral protection of the newborn foal depends on the absorption of preformed antibodies from the colostrum immediately after birth. Failure of immunoglobulin transfer via the colostrum increases the susceptibility of the foal to infection from environmental pathogens.2

Data collected by Tallmadge's team suggests that the equine neonatal immune system is nave but competent, including potential B and T helper cell preparedness for the production of all immunoglobulin isotypes, which can be explored for prophylaxis. "Although the equine neonate humoral response seems competent, B cell activation factors derived from antigen presenting cells and T cells may control critical development regulation and immunoglobulin production during the initial months of life."2

"The major question is how can the foal respond to antigens?" Felippe says. "There are some general concerns that foals do not respond very well to vaccines. Interestingly, foals that received colostrum from mares that were vaccinated during the last month of gestation had a delayed ability in their humoral response to vaccination."


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Source: DVM360 MAGAZINE,
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