Objective—To determine the effects of dexamethasone
on development of IgG subclass responses following
vaccination of healthy horses.
Animals—11 mature Thoroughbreds.
Procedure—Horses received 2 IM injections at 2-
week intervals of a vaccine containing inactivated
infectious bovine rhinotracheitis, bovine viral diarrhea,
and parainfluenza-3 viral antigens and were then randomly
assigned to 2 groups. Six horses received dexamethasone
(0.2 mg/kg of body weight, IM) twice
weekly for 8 weeks starting the day of the first vaccination.
Five control horses received an equivalent volume
of saline (0.9% NaCl) solution. Antigen-specific
serum IgG subclass titers were determined weekly
after vaccination by use of an ELISA.
Results—Vaccination resulted in similar antigen-specific
serum IgG(T) titers in dexamethasone-treated
and control horses. In contrast, although control horses
developed IgGa and IgGb responses after vaccination,
corticosteroid administration completely inhibited
these responses in treated horses.
Conclusions and Clinical Relevance—Cortico
steroids can have profound effects on primary
immune responses in horses and can significantly
affect IgG responses to inactivated vaccines.
Corticosteroid treatment regimens commonly used
to treat diseases in horses may result induction of a
nonprotective IgG subclass response, leaving treated
horses susceptible to disease. Additionally, mechanisms
regulating IgGa and IgGb responses appear to
differ from those regulating IgG(T) responses. Further
defining these mechanisms is a critical step in designing
effective vaccines, and corticosteroid-induced
immunomodulation may be a valuable tool for studying
immune responses in horses. (Am J Vet Res
Objective—To determine safety, efficacy, and
immunogenicity of an intranasal cold-adapted modified-
live equine influenza virus vaccine administered
to ponies following induction of exercise-induced
Animals—Fifteen 9- to 15-month old ponies that had
not had influenza.
Procedure—Five ponies were vaccinated after 5 days of strenuous exercise on a high-speed treadmill, 5
were vaccinated without undergoing exercise, and 5
were not vaccinated or exercised and served as controls.
Three months later, all ponies were challenged
by nebulization of homologous equine influenza virus.
Clinical and hematologic responses and viral shedding
were monitored, and serum and nasal secretions
were collected for determination of influenza-virus-specific
antibody isotype responses.
Results—Exercise caused immunosuppression, as
indicated by depression of lymphocyte proliferation in
response to pokeweed mitogen. Vaccination did not
result in adverse clinical effects, and none of the vaccinated
ponies developed clinical signs of infection following
challenge exposure. In contrast, challenge exposure
caused marked clinical signs of respiratory tract
disease in 4 control ponies. Vaccinated and control
ponies shed virus after challenge exposure. Antibody
responses to vaccination were restricted to serum
IgGa and IgGb responses in both vaccination groups.
After challenge exposure, ponies in all groups generated
serum IgGa and IgGb and nasal IgA responses.
Patterns of serum hemagglutination inhibition titers
were similar to patterns of IgGa and IgGb responses.
Conclusions and Clinical Relevance—Results suggested that administration of this MLV vaccine to
ponies with exercise-induced immunosuppression
was safe and that administration of a single dose to
ponies provided clinical protection 3 months later. (J
Am Vet Med Assoc 2001;218:900–906)