Antibody studies in ponies vaccinated with Venezuelan equine encephalomyelitis (strain TC-83) and other alphavirus vaccines.

The research article examines the influence of pre-vaccination antibodies in ponies on the stimulation of hemagglutination-inhibition (HI) antibodies by other alphavirus vaccines, specifically those for Venezuelan, Western, and Eastern equine encephalomyelitis. The conclusions drawn demonstrate variations in antibody response to vaccination based on the presence of pre-vaccination antibodies, and highlights the possibility of cross-reacting antibodies offering protection.

Study Design and Subjects

• The study involved serologic testing on 24 ponies, assessing the effect of pre-existing antibodies to Venezuelan equine encephalomyelitis (VEE) virus, strain TC-83, on the stimulation of hemagglutination-inhibition (HI) antibodies by vaccines for western equine encephalomyelitis (WEE) and eastern equine encephalomyelitis (EEE)-WEE.
• Additionally, the VEE, WEE, and EEE antibody responses in 18 VEE-vaccinated animals—13 ponies and 5 horses—were studied, 9 to 14 months after their immunity was challenged with a potent form of the VEE virus.

Findings of the Study

• It was discovered that the presence of VEE HI antibodies and neutralizing antibodies together resulted in a greater suppression of VEE antibody stimulation, compared to VEE neutralizing antibodies alone.
• In animals with pre-existing exposure only to VEE neutralizing antibodies, there was a higher increase in geometric mean antibody titers (GMT)—the average titer value on a logarithmic scale—than in those with pre-existing exposure to both types of VEE antibodies.
• Animals without detectable pre-existing VEE antibodies showed a primary immune response to VEE post exposure challenge. The observed protection in these animals might be due to high levels of cross-reactive antibodies against other types of equine encephalomyelitis—WEE or EEE or both.
• No significant fluctuations were observed in GMT for WEE HI antibodies and complement-fixation antibodies post exposure challenge. Contrastingly, a significant increase in the EEE HI-GMT occurred in ponies that had low or no pre-exposure titers of VEE antibodies.

Implications of the Study

• The study highlights the complex interplay of pre-existing antibodies on the stimulation and suppression of other antibodies through vaccination.
• The findings also hint at the possibility of cross-reacting antibodies serving as a protective measure in animals without pre-existing antibodies against a particular virus.
• These observations may provide important insights for the development and improvement of equine encephalomyelitis vaccines and potentially other alphavirus vaccines in future.