Anatomical and histological profile of bronchus-associated lymphoid tissue and localization of melatonin receptor types (Mel1a and Mel1b) in the lung-associated immune system of a tropical bird, Perdicula asiatica

The histological distribution of the lung-associated immune system (LAIS) and the expressional pattern of melatonin receptors are still unknown in birds. The aim of the present study was to determine the localization of the bronchus-associated lymphoid tissue (BALT nodule) in a tropical bird, the Indian jungle bush quail, Perdicula asiatica. We also demonstrate the expression of melatonin receptor types (Mel1a and Mel1b) in order to propose an immunomodulatory role of melatonin in LAIS. Localization of melatonin receptors in the lung of the Indian jungle bush quail, P. asiatica was supported immunohistochemically and by Western blot analysis using specific antibodies for those receptors. Immunolocalization for Mel1b receptor was noted in the bronchial region of the lungs, in finger-like projections of mucosal foldings, in lymphocytes in the BALT nodule as well as in free form. In contrast, immunolocalization for Mel1a receptor was noted in various areas of the lung instead of in the bronchial region. Western blot analysis showed a single band at 37 and 39 kDa for Mel1a and Mel1b receptors, respectively, with the latter showing higher expression. The results demonstrate a well-developed LAIS and region-specific distribution of melatonin receptors in the lung and provide evidence for a possible functional role for melatonin in the LAIS of birds.