Langerhans’ cells in equine cutaneous papillomas and normal skin.

This research article examines the presence and function of Langerhans’ cells (LC), which are immune cells of the skin, in both healthy horse skin and skin that has developed cutaneous papillomas (skin tumors). The study reveals that LC react differently depending on the stage of the tumor, presenting potential insights into virus-host interactions and tumor development and regression in equine skin.

Study Methodology

• The researchers induced cutaneous papillomas — a type of benign, noncancerous skin tumor — in five 2-year-old Thoroughbred horses to study the role of LC cells in normal and abnormal skin context.
• The study used immunohistochemical and electron microscopic techniques to investigate LC in normal horse epidermis (outer layer of skin) and the induced papillomas.

Findings in Normal Skin

• In the normal epidermis of the horse skin, Class II major histocompatibility complex antigen-positive dendritic LC were found. These are a particular subset of LC known for presenting antigens (foreign substances) to T cells — a vital part of the immune response.
• Under an electron microscope, these LC displayed the characteristic Birbeck’s granules, which are unique structures found within Langerhans’ cells.

Findings in Developing Phase of Papillomas

• The developing phase of the papillomas showed a notable decrease in the size and quantity of LC, indicating a hypofunctional state, or a less active state of these immune cells.

Findings in Regressing Phase of Papillomas

• As the papillomas started to regress, there was a substantial increase in the number of LC, particularly at where the outer layer of the skin (epidermis) and underlying skin layer (dermis) meet.
• These LC featured long dendrites and had abundant cytoplasm with well-developed cytoplasmic organelles. The organelles especially highlighted included Golgi apparatus, lysosomes, Birbeck’s granules, and multivesicular bodies, indicating a hyperfunctional state, or highly active.
• The junction between epidermis and dermis also showed a surge of many T lymphocytes, which are central players in the immune response.

The study discloses a potential link between the behavior and number of Langerhans’ cells and the development and regression of cutaneous papillomas in horses. This understanding could lead to potential interventions or treatments in the future.