Immune complexes in purpura hemorrhagica of the horse contain IgA and M antigen of Streptococcus equi.

The research study is suggesting that the disease Purpura hemorrhagica in horses, which is often associated with the upper respiratory tract condition strangles, may be an immune complex-mediated condition. This is based on findings of particular immune complexes in the blood serum of these affected horses.

Introduction of Purpura Hemorrhagica and Strangles

• Purpura hemorrhagica is a severe disease that can affect horses, characterized by swelling of the head and limbs, vasculitis (inflammation of the blood vessels), petechial hemorrhages (small, purple-red spots caused by bleeding into the skin), and sometimes, kidney inflammation.
• Strangles is another equine disease that affects the upper respiratory tract, caused by the bacterium Streptococcus equi. There’s a known association between strangles and purpura hemorrhagica, where the latter often follows an episode of the former.

Research Methodology

• The team collected serum from horses suffering from purpura hemorrhagica following a strangles infection. Serum is the clear, pale-yellow liquid that remains after blood has clotted.
• They used Polyethylene Glycol (PEG) precipitation, a technique to concentrate and isolate protein molecules like antibodies, to identify the presence of immune complexes in these samples.
• Western blot analysis, a highly sensitive technique used to detect specific proteins from a complex mixture, was employed to characterize the immune complexes.

Findings and Proposal

• The immune complexes detected in the horse sera contained Immunoglobulin A (IgA), a type of antibody that plays a crucial role in the immune function of mucous membranes, and specific antigens of Streptococcus equi resembling those found in acid extracts.
• Based on these findings, the research team proposes that purpura hemorrhagica might not be just a simple reactive condition or a delayed hypersensitivity reaction following a streptococcus equi infection. Rather, it could be perceived as an immune complex–mediated disease, where the immune system mistakenly attacks body cells after reacting with the circulating Streptococcus equi antigens.