Al-Tikriti MS, Khamas WA and Henry RW
Background: Bronchial associated lymphoid tissue (BALT) is present in humans and several other animal species including the cat which was reported that only present during infection. The role of BALT in antigen uptake and immune response is well established, and its location is varied in different species. The aim of this study was to investigate the presence and morphology of healthy cat lungs lymphoid tissue using traditional light microscopical techniques.
Methods: Tissues were collected from all lung lobes from (2 to 3 years old) healthy domestic cats and processed using standard histological techniques. The tissues were cuts into small pieces and embedded in an Epon-Araldite mixture. Tissue sections were stained with hematoxylin and eosin, and periodic acid Schiff stains.
Results: The majority of lymphatic tissue was located along the bronchial tree and associated neurovascular bundles. Both nodular and diffuse forms were present in healthy domestic cats. These lymphoid tissues extended distally into the wall of terminal bronchioles. The nodules had distinct marginal and central areas and were located in the tunica adventitia of the bronchi, bronchioles and diffusely infiltrated the adventitia of the wall of adjacent blood vessels. However, a diffuse form was found primarily in the submucosa of the bronchial tree intermingled with the submucosal glands. In addition, the diffuse form was also located around bronchioles, blood vessel and alveoli.
Conclusion: This study shows presence of diffuse and nodular forms of lymphoid tissues within the lungs of a healthy cat. The nodular form was not only associated with bronchial tree all the way down to terminal bronchioles, but also with veins, arteries and parenchyma of the lungs. Hence, PALT (Pulmonary Associated Lymphatic Tissue) seems to be a better nomenclature than BALT to describe the relationship and distribution of the distal lymphatic tissue in the lungs of healthy domestic cat.