Expression characteristics of polymeric immunoglobulin receptor in Bactrian camel (Camelus bactrianus) lungs

Polymeric immunoglobulin receptor (pIgR), the transmembrane transporter of polymeric immunoglobulin A and M, has multiple immune functions. To explore the characteristics of pIgR expression in Bactrian camel lungs, twelve healthy adult (2-7 years old) Bactrian camels were systematically studied. The results showed that pIgR was mainly expressed in the cytoplasm and membrane of ciliated cells, as well as in the cytoplasm and membrane of basal cells, serous cells of bronchial glands, club cells and alveolar type 2 cells in Bactrian camel lungs. Specially, as the bronchial branches extended, the pIgR expression level in ciliated cells significantly declined (p<0.05), and the corresponding bronchial luminal areas obviously decreased (p<0.05). However, pIgR was not expressed in goblet cells, endocrine cells, alveolar type 1 cells and mucous cells of bronchial glands. The results demonstrated that ciliated cells continuously distributed throughout the whole bronchial tree mucosa were the major expression sites of pIgR, and pIgR was also expressed in basal cells, serous cells of bronchial glands, club cells and alveolar type 2 cells, which would facilitate secretory immunoglobulin A (SIgA) transmembrane transport by pIgR and form an intact protective barrier. Moreover, the pIgR expression level in ciliated cells was positively correlated with the bronchial luminal areas; but negatively correlated with the cleanliness of airflow through the bronchial cross-sections, showing that the pIgR expression level in the bronchial epithelium was inhomogeneous. Our study provided a foundation for further exploring the regulatory functions of immunoglobulins (i.e., SIgA) after transport across the membrane by pIgR in Bactrian camel lungs.