Chemotactic response of equine polymorphonuclear leucocytes to Streptococcus equi.

The research article explores how horse immune cells, specifically polymorphonuclear leucocytes (PMNs), react to infection from the bacterium Streptococcus equi. The study dives deep into the mechanisms involved in the immune response, notably in the chemotactic behavior of PMNs.

Chemotaxis and PMNs in Response to Streptococcus equi Infection

• The researchers began by detailing the typical response of horses to Streptococcus equi infection. The lymph nodes of the infected horses are intensely infiltrated by polymorphonuclear leucocytes (PMNs), indicative of a strong chemotactic response by these immune cells to the bacteria or its components.
• To better understand this reaction, equine PMNs were separated using Ficoll-Hypaque medium, then used in an assay (a kind of laboratory test) to measure chemotaxis under agarose, a gel used for laboratory tests. This was done to examine the specific components of Streptococcus equi that trigger this immune response.

Role of Complement-derived Chemotactic Factors

• Results from the experiment indicate that chemotactic factors derived from what’s known as the “alternative complement pathway” play a significant part in causing PMNs to migrate towards the pathogen.
• Both the complete form of the bacteria and synthesized arrangements of its cell wall (peptidoglycan preparations) were found to be effective in activating this complement system. In comparison, a specific protein from the bacteria, known as ‘M protein’, was less effective in activating the complement pathway.

The Impact of S. equi Culture Supernatant Protein on PMNs

• The research revealed an interesting phenomenon where a certain protein in the bacteria’s culture supernatant (the liquid part left after removing the bacteria) didn’t activate the complement system, but rather directly impeded the movement of PMNs.
• Additionally, when the PMNs were introduced to the culture supernatant of a non-hemolytic (a strain of bacteria that does not cause red blood cell lysis) strain of S. equi, the cells showed symptoms of degeneration, suggesting the presence of a cytotoxin (a substance toxic to cells) that is different from hemolysin (a substance that causes red blood cell lysis).