Association of Streptococcus equi with equine monocytes.

The research article discusses how Streptococcus equi, a bacterium causing the horsey disease ‘strangles’, is infiltrated and eliminated by equine blood monocytes, leading to the possibility that these monocytes transport the bacteria from tonsil to local lymph nodes.

Background and Purpose

• The focus of this study is Streptococcus equi (Se), a bacterium known to cause a disease in horses called ‘strangles’. This bacterium generally resists being ingested and destroyed by a type of white blood cell called neutrophils, and thus it has been usually represented as an extracellular pathogen.
• The article aims to outline, with supportive evidence, the process by which the body of a horse eventually defeats this resilient bacterium. It postulates that equine blood monocytes, a type of white blood cell, play a key role in this process.

Methodology

• The researchers conducted various assays and used techniques like cytometry and confocal microscopy to analyze and demonstrate the behavior of Streptococcus equi and equine blood monocytes.

Findings

• The study reveals that despite Se’s resistance to neutrophils, it is eventually internalized and eradicated by equine blood monocytes. This process happens during the convalescence period when the horse is recovering from the acute phase of the disease. During this time, the large numbers of the organism found within tonsillar tissues are completely removed.
• The specific mechanism by which this happens is still unknown.

Implications

• This discovery points to a probable role of tonsillar macrophages, which are a form of monocytes, in adaptive immune clearance. This means these cells may have a role in the horse’s immune response, specifically in identifying, targeting and eliminating the Se bacteria.
• Additionally, the study suggests a possible pathway for the bacteria’s journey within the horse’s body. It raises the hypothesis that monocytes could serve as vehicles for transport of the bacteria from the tonsil and to local lymph nodes, thus potentially spreading the infection.