Cell-mediated immune responses in horses with equine protozoal myeloencephalitis.

This research explored the immune responses in horses affected by equine protozoal myeloencephalitis (EPM), a neurologic syndrome. A significant difference was discovered in the capability of horses’ lymphocytes to respond to a protein found in the parasite causing the disease, possibly suggesting that the parasite could suppress responses to its own antigens.

Introduction to Equine Protozoal Myeloencephalitis (EPM)

• The study is focused on EPM, a neurological condition predominantly affecting horses in the Americas. This disease is usually caused by a parasite named Sarcocystis neurona.
• It has been observed that horses with EPM display lowered cell-mediated immune responses (the body’s defense system involving cells that can directly kill other cells or help in the elimination of antigens) to mitogens (substances that stimulate cell proliferation).
• However, whether the EPM-causing parasite itself induces this immunosuppression or whether such immune suppression facilitates the disease manifestation remains unclear.

The Study and Methodology

• The researchers focused on a 29-kDa surface antigen from Sarcocystis neurona merozoites (known as SnSAG1), previously identified as highly active in stimulating an immune response.
• The test included isolated peripheral blood lymphocytes from 43 EPM-negative horses and 28 EPM-positive horses. These were cocultured with a mitogen or SnSAG1, letting the researchers measure the lymphocyte responses to the antigens.
• Gamma-interferon (gammaIFN) production was also measured as it is a crucial element of the immune system’s defence against viruses and other pathogens.

The Findings

• The examined lymphocyte responses to ConcanavalinA (a commonly used mitogen) showed no significant differences between EPM-positive and EPM-negative horses.
• However, in the case of SnSAG1, lymphocytes from EPM-negative horses showed significantly higher responses than those from EPM-positive horses.
• The study also observed that gammaIFN production in response to SnSAG1 was detectable within 24 hours in all EPM-negative horses, but no such gammaIFN production was detectable in EPM-positive horses, even after 72 hours.
• This suggests that the parasite might induce an immunosuppressions toward its own antigens, observed as reduced parasite-specific responses.