The Distribution Characteristics of IgA and IgG Antibody-Secreting Cells in the Pharyngeal Tonsils of Bactrian Camels of Different Ages
Authors: Fang Ying-Dong , Xie Fei , Zeng Wei-Wei , Lu Jia , Cheng Yu-Jiao , Zhang Wang-Dong , Wang Wen-Hui 
Published: October 2023

Abstract
Background: The pharyngeal tonsils, located in the nasopharynx, can effectively defend against invading pathogens of the upper respiratory tract, and play an important role in mucosal immunity of the respiratory tract. IgA and IgG are two important effector molecules of mucosal immunity, and have multiple immune functions. This study aimed to explore the distribution patterns of IgA and IgG antibody-secreting cells (ASCs) in the pharyngeal tonsils of Bactrian camels of different ages. Twelve Alashan Bactrian camels were divided into the following three age groups: young (1-2 years), pubertal (3-5 years) and middle-aged (6-16 years). The structural features of the pharyngeal tonsils were carefully observed by anatomical and histological methods, the age-related distribution of IgA and IgG ASCs in the pharyngeal tonsils was detected and compared using immunohistochemical techniques, and their densities were analyzed using statistical methods.
Results: The results showed that the pharyngeal tonsils of Bactrian camels were located at the posterior wall of the top of the nasopharynx, and mainly composed of epithelium and lamina propria. The epithelium was mainly pseudostratified ciliated columnar epithelium. Interestingly, some of the epithelium was infiltrated by immune cells, forming the reticular epithelium. There were connective tissues and abundant lymphoid tissues in the lamina propria, and a few blood vessels, groups of glands and their excretory ducts were distributed among the connective tissue. In the pharyngeal tonsils of all age groups, IgA and IgG ASCs were mainly clustered or diffusely distributed in the subepithelial regions of reticular epithelium (region A) and around the glands (region C), scattered in the subepithelial regions of nonreticular epithelium (region B), and distributed sporadically in the extrafollicular regions (region D). Their distribution densities in these four regions were significantly decreased in turn (P<0.05). However, the densities of IgA ASCs were significantly higher than IgG ASCs in the same region (P<0.05), and the distribution densities of these two ASCs in each region of the pharyngeal tonsils gradually increased from young to pubertal group, reached a peak in the pubertal group, and then gradually decreased with age.
Conclusions: The results confirmed that IgA and IgG ASCs were distributed in each region of the pharyngeal tonsils of Bactrian camels, which were conducive to forming a complete immune defense barrier in the pharyngeal tonsils, but the subepithelial regions of reticular epithelium and glandular regions in the pharyngeal tonsils were the primary regions for the colonization and exertion of immune function of IgA and IgG ASCs. IgA might be a significant component of mucosal immune responses in the pharyngeal tonsils of Bactrian camels. These findings will provide support for further studies on the immunosenescence and immune response mechanisms of pharyngeal tonsils of Bactrian camels.