Immune-Mediated Muscle Diseases of the Horse.

The research article explores immune-mediated muscle diseases in horses caused either by an exaggerated immune response to infections or a mistaken immune response to the animal’s own muscle proteins. It elaborates on different types of such disorders, their clinical features, pathological characteristics and the supposed underlying mechanisms.

Overview of Immune-Mediated Muscle Disorders in Horses

• The study discusses immune-mediated muscle diseases in horses. These conditions arise due to the immune system’s overactive response to infections, or mistakenly responding to the horse’s own muscle proteins. The immune system, in attempting to protect the body, ends up damaging its cells.

Infarctive Purpura Hemorrhagica (IPH)

• The paper first talks about Infarctive Purpura Hemorrhagica (IPH), a condition that happens in response to infection or vaccination with Streptococcus equi ss. equi – a bacterium.
• IPH leads to the formation of harmful complexes of a protein from Streptococcus and an immune molecule (IgA). This subsequent accumulation in blood vessels results in the obstruction of blood flow and, eventually, the death of muscle and organ tissue due to lack of oxygen and nutrients (ischemia and infarction).

Immune-Mediated Myositis in Quarter Horse-Related Breeds

• The next condition the researchers discuss is immune-mediated myositis found primarily in Quarter Horse-related breeds.
• It appears that an abnormal immune response to muscle proteins triggers an increase in the expression of major histocompatibility complex class I and II on muscle cells. These are proteins involved in immune response and act as ‘flags’ for immune cells to recognize foreign bodies.
• This leads to immune cells filtering into the muscles and causing muscle fibre damage, particularly in the lumbar and gluteal regions, and eventually, significant muscle loss (atrophy).

Myositis leading to Systemic Calcinosis

• In rare instances, an inflammatory episode can lead to myositis that further progress to systemic calcinosis – a condition characterized by abnormal calcium deposits in various body tissues.
• This is marked by an excessive amount of phosphate in the blood (hyperphosphatemia), and unfortunately, is associated with a high mortality rate.

Conclusion

• The review provides an insight into the immune-mediated muscular disorders in horses, shedding light on their clinical signs and pathological characteristics.
• The study also suggests potential underlying mechanisms that excite these conditions, which could later lead to their improved understanding and treatment strategies.