Unusual patterns of serum antibodies to Streptococcus equi in two horses with purpura hemorrhagica.

This research aimed to develop an assay to measure the level of antibodies against Streptococcus equi (a bacterial pathogen in horses) in the serum, and noticed unusual antibody patterns in two horses with purpura hemorrhagica.

Development of the Enzyme-Linked Immunosorbent Assay (ELISA)

• An ELISA test was developed specifically for use in horses. This test was designed to determine the levels, or ‘titers’, of different classes of antibodies (IgA, IgG, and IgM) in the serum of the horses.
• These antibodies were targeted against two different antigens: an M-like protein and a protein found in culture supernatant – both associated with the S. equi pathogen.

Study Population and Antibody Levels

• 28 adult horses were included in the study. The group was divided into three:
• 9 horses had recent infections with S. equi;
• 17 horses had no known exposure to S. equi and also no history of respiratory disease in the preceding four months;
• 2 horses had purpura hemorrhagica, a severe complication of S. equi infection.
• In the group of recently infected horses, the IgA antibodies against the culture supernatant protein were found to be at the highest levels (significantly higher than the other groups at P less than 0.001). This suggests that this particular antibody may play a role in the immune response to an active S. equi infection.

Antibody Patterns in Horses with Purpura Hemorrhagica

• In the two horses with purpura hemorrhagica, an unusual pattern was noted: Initially, the levels of IgG antibodies against both tested antigens (the S. equi M-like protein and the culture supernatant protein) were undetectable.
• However, as these horses started to recover clinically from purpura hemorrhagica, these IgG levels started to rise.
• The paper concludes by discussing potential mechanisms that could explain these findings, indicating that the immune response in purpura hemorrhagica may be different or delayed compared to a typical S. equi infection.