Streptococcus equi but not Streptococcus zooepidemicus produces potent mitogenic responses from equine peripheral blood mononuclear cells.

This paper explores the impact of two bacteria strains, Streptococcus equi and Streptococcus zooepidemicus, on equine health. The study found that S. equi stimulates stronger responses from horse immune cells than S. zooepidemicus, potentially contributing to severe symptoms of a horse disease called strangles.

Background

• Equine strangles is a respiratory tract disease in horses caused by the bacteria Streptococcus equi.
• The acute phase of equine strangles can mimic symptoms of an acute illness response, including elevated body temperature, augmented plasma fibrinogen levels and an increase in a type of white blood cell called neutrophils.
• These symptoms are mediated by proinflammatory cytokines, which are small proteins released by cells that have specific effects on communication and interactions between cells.
• These effects can include cellular growth, death, differentiation, and immune response activation.

Aim of the Research

• The researchers aimed to observe the immune response in horse peripheral blood mononuclear cells (PBMCs) when introduced to S. equi and S. zooepidemicus strains isolated from equine patient cultures.
• The specific cell reaction they looked for was a mitogenic response, which is a reaction that stimulates cells to divide and proliferate.

Findings

• The researchers found a strong mitogenic response in horse PBMCs when introducing S. equi comparable to the response seen from the introduction of a benchmark substance, Concanavalin A.
• However, there was no such response elicited by the introduction of S. zooepidemicus to the PBMCs.
• The researchers also found that the mitogenic effect from S. equi was neutralized by Proteinase K, an enzyme that breaks down proteins, and by a serum obtained from recovering strangles patients.

Conclusion

• The study suggests that the release of proteinaceous immunogenic mitogens by S. equi along with the unique antiphagocytic protein SeM may play a crucial role in the severe clinical manifestations of acute strangles in horses.
• Overall, these findings have important implications for the broader understanding of the specific pathogenic mechanisms of S. equi and how the disease strangles can be targeted for future treatments.