Cellular architecture of the synovium in the tendon sheath of horses: an immunohistochemical and scanning electron microscopic study.

The study examines the cell architecture of the synovium, a layer of tissue found in the tendon sheath of horses. By employing both histochemistry and scanning electron microscopy, researchers discovered that the structure of this area is similar to the synovium found in joints, composed of two types of cells, indicated as A and B.

Methodology

• The researchers investigated the properties and organization of synovial cells that encase the tendon sheath in the anatomy of horses.
• To achieve this, they utilized various techniques including histochemistry, a technique that combines biochemistry and histology to categorize biological tissues, and scanning electron microscopy (SEM), a kind of microscopy that enables the visualization of minute specimens in high resolution.

Findings

• The findings indicate that the inside layer of the tendon sheath, similar to a joint, is covered in a rich layer of cells, which are referred to as the intimal layer.
• They found A cells to be abundant in the mesotendon (the connective tissue between tendons), but rather sparse in other areas. These cells were recognized by their positivity for acid phosphatase, an enzyme found in lysosomes.
• The B cells, on the other hand, were identified through their interaction with a protein gene product (PGP) 9.5 antiserum and were observed throughout the entire synovial intima in the tendon sheath.

Types of B Cells

• Researchers also found two subtypes of B cells, differentiated by their structural appearance and behavior using scanning electron microscopy.
• Dendritic-type B cells were primarily found on the joint side of the tendon sheath, and extended branched structures to form a surface meshwork on the intimal surface.
• Flat-type B cells, in contrast, were found in the skin-side area of the tendon sheath as well as in the mesotendon. Their membranous expansions extended horizontally, covering the surface of the intimal layer, similar in appearance to epithelium.

Conclusion

• The study indicates that the morphology (form and structure) and distribution of synovial intimal cells could likely be influenced by diverse factors such as the individual characteristics of the underlying tissues and the degree of mechanical stress being applied.
• The findings shed light on the complex cellular architecture of the synovium in the tendon sheath of horses, providing potential insight into the structural and functional aspects of similar structures across different species.