Epithelial lymphocyte and macrophage distribution in the adult and fetal equine lung.

This research article explores the distribution of immune cells in the lungs of adult and fetal horses, finding that adult horses have a higher number of T cells in areas exposed to airborne antigens, while fetal horses have fewer T cells and lower levels of a specific immune marker, suggesting that exposure to airborne stimuli is necessary for the development of the fetal immune system.

Research Methodology and Participants

• The study examined the distribution of immune cells in the lung epithelium of four horses: two adults, a pregnant mare, and her fetus nearing the end of gestation.
• Immunohistochemical analysis was used to assess the distribution of lymphoid and myeloid cells in the respiratory tracts of the horses.
• Using monoclonal antibodies, the researchers investigated the presence of T-cells, B-cells, and macrophage/dendritic myeloid cells, along with Major Histocompatibility Class (MHC) II surface antigens.
• Distribution and cell numbers were determined by microscopy.

Findings in Adult Horses

• The number of epithelial T cells decreased consistently from the upper to the lower respiratory tract in the adult horses.
• MHC Class II was expressed on the airway epithelium of the two adult horses.
• Most of the cells associated with the epithelium were not labeled by antibodies identifying B cells or myeloid cells; an antibody identifying mature equine alveolar macrophages (ED2) was utilized for the first time in this study.

Findings in Fetal Horse

• The fetal horse had a lower number of T cells, which did not vary greatly in different parts of the respiratory tract.
• MHC Class II expression was not seen on the airway epithelium of the fetal horse. Occasionally, large, irregularly-shaped, Class II-positive cells were identified.

Interpretation of Findings

• The researchers suggest that the distribution of T cells in adult horses might be due to the higher contact with airborne antigens.
• In contrast, the fetal immune system had fewer T cells and lower MHC II expression, which could be due its lack of exposure to airborne stimuli. This supports the idea that such exposure is crucial for the full development of the immune system.
• The low level of MHC Class II expression in the pregnant mare might be indicative of immune suppression, which is commonly associated with pregnancy.