Sub-isotypic differences in the immunoglobulin G response to Lawsonia intracellularis in vaccinated, seropositive, and equine proliferative enteropathy-affected horses.

The research study investigates the immune system responses of horses following infection with Lawsonia intracellularis (a bacteria responsible for diseases like the Equine Proliferative Enteropathy). The study finds variability in the production of IgG, a class of antibody responsible for fighting such infections, and its subtypes in horses categorised as: clinically affected, vaccinated, or just exposed to the bacteria.

Study Rationale and Aims

• L. intracellularis causes EPE (Equine Proliferative Enteropathy), a disease that while mostly mild, can potentially be life-threatening in horses, especially in weanlings. This study was aimed at understanding the systemic immune response of horses against the bacteria.
• It was hypothesised that different classes of the equine antibody IgG (namely IgG(a), IgG(b), and IgG(t)) may be differentially produced in response to infection, exposure, or vaccination, thus impacting disease outcome.
• Thus, the goal was to see whether clinical manifestations of EPE were correlated with particular IgG isotypes.

Methodology

• Horses were classified into three groups based on their interaction with L. Intracellularis – those who were merely exposed (seropositive-only), those explicitly infected and showing symptoms (presumptive clinical EPE) and vaccinated horses.
• A special ELISA (Enzyme-Linked Immunosorbent Assay) method was developed to check for the presence of IgG and its isotypes.

Results

• The results showed that horses clinically affected by EPE produced significantly more total IgG and IgG(a) when compared to exposed or vaccinated horses.
• The vaccinated horses had significantly more IgG(b) than the other two categories, suggesting that this could be the desired immune response from vaccination.
• Interestingly, none of the groups were found to have the isotype IgG(t).

Implications and Future Directions

• The results signify an interesting pattern in the immune response to L. intracellularis infection. The overrepresentation of certain IgG isotypes in the different groups of horses opens up new avenues of research.
• With further study, these differences might help in the development of more effective vaccination and treatment protocols against EPE.
• Due to certain limitations in reagent availability, it was not possible to check for a broader range of IgG sub-isotypes, which might be a possible future direction for further research.