Equine Neonates Have Attenuated Humoral and Cell-Mediated Immune Responses to a Killed Adjuvanted Vaccine Compared to Adult Horses

Abstract

The objectives of this study were to compare relative vaccine-specific serum immunoglobulin concentrations, vaccine-specific lymphoproliferative responses, and cytokine profiles of proliferating lymphocytes between 3-day-old foals, 3-month-old foals, and adult horses after vaccination with a killed adjuvanted vaccine. Horses were vaccinated intramuscularly twice at 3-week intervals with a vaccine containing antigens from bovine viral respiratory pathogens to avoid interference from maternal antibody. Both groups of foals and adult horses responded to the vaccine with a significant increase in vaccine-specific IgGa and IgG(T) concentrations. In contrast, only adult horses and 3-month-old foals mounted significant vaccine-specific total IgG, IgGb, and IgM responses. Vaccine-specific concentrations of IgM and IgG(T) were significantly different between all groups, with the highest concentrations occurring in adult horses, followed by 3-month-old foals and, finally, 3-day-old foals. Only the adult horses mounted significant vaccine-specific lymphoproliferative responses. Baseline gamma interferon (IFN-␥) and interleukin-4 (IL-4) concentrations

Rhodococcus equi: Clinical Manifestations, Virulence, and Immunity

“…74,75 However, recent data demonstrate that foals are also deficient in their ability to produce IL-4 in response to stimulations with mitogens and after vaccination with a killed adjuvanted vaccine, suggesting that a clear polarization toward a Th2 response is unlikely in neonatal foals. [78][79][80] Consistent with these findings, experimental infection of young foals with virulent R. equi results in IFN-c induction and antibody responses similar to or greater than that of adult horses undergoing the same experimental challenge. 81 Recent studies have investigated various immunostimulants that might enhance host defense mechanisms during the relatively narrow period of susceptibility to R. equi.…”

“…In particular, the finding that young foals are deficient in their ability to produce IFN‐γ in response to mitogens has led to the hypothesis that an IFN‐γ deficiency and Th2 bias might be at the basis of their peculiar susceptibility to R. equi infections . However, recent data demonstrate that foals are also deficient in their ability to produce IL‐4 in response to stimulations with mitogens and after vaccination with a killed adjuvanted vaccine, suggesting that a clear polarization toward a Th2 response is unlikely in neonatal foals . Consistent with these findings, experimental infection of young foals with virulent R. equi results in IFN‐γ induction and antibody responses similar to or greater than that of adult horses undergoing the same experimental challenge …”

Antibody to Poly-N-acetyl glucosamine provides protection against intracellular pathogens: Mechanism of action and validation in horse foals challenged with Rhodococcus equi

“…A final premise justifying immunizing pregnant mares to evaluate vaccine-induced immunity to R . equi is that foals are considered to be infected soon after birth [ 22 ] when they are more susceptible to infection [ 23 ] and when their immune system is less effective in responding to vaccines [ 10 , 24 – 26 ]. This precludes active immunization of very young foals as a strategy for vaccine evaluation against R .…”

Antigen-specific immunoglobulin variable region sequencing measures humoral immune response to vaccination in the equine neonate

“…Fully mature, functional, and protective immune responses to certain types of vaccines have been reported during the neonatal period in foals, calves, piglets, and fox puppies, suggesting that the use of immunization strategies at this developmental stage has value [ 24 – 28 ]. Indeed, administration of vaccines with adjuvant to neonatal foals as young as 1–6 days old revealed antigen-specific IgG responses [ 29 , 30 ]. In contrast, current vaccination guidelines for horses recommend initiating vaccinations at 3 months of age, and delaying foal vaccination to at least 6 months of age when the dam was vaccinated with the respective vaccine in the last month of gestation; these recommendations aim to overcome a potential maternal antibody interference with the foal’s humoral response (AAEP Vaccination Guidelines Review Task Force, 2015; http://www.aaep.org/custdocs/Foal%20Vaccination%20Chart_8.12.16.pdf ).…”