Comparison of antibody and cell-mediated immune responses of foals and adult horses after vaccination with live Mycobacterium bovis BCG.
BACKGROUND
Equine neonates have reduced humoral and cell-mediated immune responses compared to adult horses after administration of killed vaccines. As a basis for this study, we hypothesized that newborn foals can mount strong immune responses after vaccination with live Mycobacterium bovis BCG.


METHODS
Healthy 4-day-old foals (n=7), 4-month-old foals (n=7) and adult horses (n=6) were vaccinated once with live M. bovis BCG. Age-matched animals (n=5 per group) were used as unvaccinated controls. Relative vaccine-specific immunoglobulin concentrations and whole blood mRNA expression of IFN-γ, IL-4, and IL-10 were measured prior to and 2, 4, 6, and 8 weeks after vaccination. Eight weeks after vaccination, delayed type hypersensitivity (DTH) responses were assessed by measuring the increase in double skin thickness after intradermal injection of purified protein derivative.


RESULTS
Both groups of foals and adult horses responded with a significant increase in vaccine-specific total IgG, IgGa, IgGc, IgG(T), and IgM concentrations. In contrast, only adult horses mounted significant IgGb responses. Vaccine-specific concentrations of total IgG and IgGa were significantly higher in adult horses than in 4-day-old foals whereas IgGc responses were significantly higher in 4-day-old foals than in the other two age groups. Adult horses had significantly higher basal IFN-γ and IL-4 mRNA expression than both groups of foals but vaccination with M. bovis BCG did not significantly increase expression of these cytokines, regardless of age group. Immunized horses had significantly higher DTH responses than age-matched unvaccinated controls. DTH responses were significantly greater in both groups of vaccinated foals than in vaccinated adult horses.


CONCLUSIONS
Despite a naïve immune system, newborn foals have the ability to mount robust antibody and cell-mediated immune responses to M. bovis BCG.
Department of Large Animal Medicine, University of Georgia, Athens, GA, United States.
Tracy L
TL
Sturgill
Department of Large Animal Medicine, University of Georgia, Athens, GA, United States. Electronic address: gigueres@uga.edu.
Steeve
S
Giguère
Department of Large Animal Medicine, University of Georgia, Athens, GA, United States.
Londa J
LJ
Berghaus
Department of Population Health, University of Georgia, Athens, GA, United States.
David J
DJ
Hurley
Department of Infectious Diseases, University of Georgia, Athens, GA, United States.
Mary K
MK
Hondalus
D000367:Age Factors; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D001500:BCG Vaccine / Q000009:adverse effects / Q000276:immunology*; D016207:Cytokines / Q000276:immunology; D006736:Horses / Q000276:immunology*; D006968:Hypersensitivity, Delayed / Q000139:chemically induced; D007111:Immunity, Cellular; D056724:Immunity, Humoral; D009163:Mycobacterium bovis; D014611:Vaccination / Q000662:veterinary*
D000907:Antibodies, Bacterial; D001500:BCG Vaccine; D016207:Cytokines
Adaptive immunity; Foal; Horse; Mycobacterium bovis BCG; Neonatal vaccination