Mucosa-associated Lymphoid Tissue Structure And Function In The Respiratory Tract And The Conjunctiva Of The Bactrian Camel(Camelus Bactrianus)

The mucosa-associated lymphoid tissue structure and function in the respiratory tract and the conjunctiva of the adult Chinese Alashan Bactrian camel (Camelus bactrianus) were investigated using the technologies of anatomy, histology, histochemistry, electron microscopy and immunohistochemistry. The results of anatomical, microstuctural, ultrastructural and immunohistochemical characteristics of the mucosa in the camel show as follows:1. The NALT in the camel could be categorized into six different types:tonsils, isolated lymphoid nodules, dense aggregations of lymphoid cells, scattered lymphoid cells, intra-epithelial lymphoid cells and free luminal lymphocytes. "Waldeyer ring" in the camel include the palatine tonsil (tonsilla palatina), the lingual tonsil (tonsilla lingualis) and the tonsil of the soft palate (tonsilla veli palatini) in the oropharynx, the pharyngeal tonsil (tonsilla pharyngea) and the tubal tonsil (tonsilla tubaria) in the nasopharynx, and the paraepiglottic tonsil (tonsilla paraepiglottica) in the laryngopharynx. The tonsils consisted of scattered lymph nodules, aggregations of lymphocytes and diffuse lymphoid tissue. Secondary lymphoid nodule was comprised of four areas: follicle-associated epithelium (FAE), dome area (DA), follicular area (DA) and parafollicular area (PFA). The lingual tonsil, the tonsil of the soft palate and the tubal tonsil were macroscopically invisible macroscopically. Because of closely adjacent anatomical position, the palatine tonsil and the paraepiglottic tonsil were lined with stratified squamous epithelium. The pharyngeal tonsil and the tubal tonsil were lined with pseudostratified columnar ciliated epithelium. The palatine tonsil possessed a large number of obvious crypts which increased the epithelial surface area potentially exposed to antigen.The surface of the soft palate were lined with stratified squamous non-keratinized epithelium. Depressions on the outer free surface led into holes or small crypts with small openings. The epithelium of the tubal tonsils in the camel composed of lymphocytes, ciliated cells, M cells basal and microvillus cells. The lingual tonsil was consisted of small aggregations of lymphocytes. The germinal centre of the lymphoid follicles comprised of Lymphoblasts, small lymphocytes, follicular dendritic cells and few macrophages, which was occupied by densely packed cells and appeared less electron dense than the rest of the follicle. Lymphoblasts with a larger cytoplasm, including several mitochondria, and had an more euchromatic nucleus which could still be round or assumed an irregular shape. FDC sent long cytoplasmic processes between the lymphoid cells. The nucleui of FDC were irregular. The cytoplasm of these cells contained the usual organelles together with frequent vesicles. CD3 and CD20 positive lymphocytes, CD68 positive macrophages were distributed in the tubal tonsil of the camel. The positive FDC were only found in germinal centres. The results suggested that NALT in the camel has the cytologic basis of normal mucosa reaction, and may play a major role in immune responses.2. The LTALT in the camel was composed of lymphoid nodules, dense aggregations of lymphoid cells, scattered lymphoid cells and intra-epithelial lymphoid cells. The lymphoid nodules were present in the mucosa of vestibulum laryngis, cavum infraglotticum and in the rostral third of the trachea. Secondary lymphoid nodule consists of four areas:follicle-associated epithelium (FAE), dome area (DA), follicular area (FA) and parafollicular area (PFA). The FAE was relatively thin and no cilia, permeated by groups of lymphoid cells. The DA was relatively thick and formed apical caps which the top faced to epithelium. The nucleui of cells in DA were darkly stained. The FA was composed of numerous lymphocytes, FDC, few macrophages and capillary.The distribution of HEV was observed in the PFA.The lymphoid nodules were also distributed in the false vocal cords (FVC). CD3 and CD20 positive lymphocytes, CD68 positive macrophages were distributed in the FAE and follicals at different ratio. The positive FDC were only found in FA.The results revealed that the presence of lymphoid nodue and inflammatory cells in the FVC was common, and was part of the normal histological morphology of larynx in the camle. LTALT composed the integrated mucosal immune system as essential component of defense in the camel upper respiratory tract. The FVC may participate in the protection of the larynx of the camel. The BALT from all detected healthy adult camel was composed of dense aggregations of lymphoid cells, scattered lymphoid cells in the mucosa of bronchi, bronchiole and terminal bronchiole. No distribution of lymphoid nodules was detected in samples from normal adult camel.The trachea of camel consists of 69-74 incomplete cartilaginous rings of hyaline. The trachea was lined with pseudostratified columnar ciliated epithelium. A dense mat of cilia covered the trachea. The motile cilium has the classical 9+2 pattern in trachea. The epithelium was composed of ciliated, goblet and basal cells. The nuclei in the ciliated cells were flat and an abundant number of mitochondria.Goblet cells contained big nuclei and secretory granules that were different in number, size and electron density. Inter-epithelial granulocytes and lymphocytes were regularly found. Lamina propria and submucosal layer were loose connective tissue with prominent elastic fibres. The mucosal and submucosal layers were 536.4±83.8μm (n=27) thick. Submucosal glands were tubuloalveolar with mucous (acidic and neutral) secretions. Submucosal gland orifices were frequently observed on the surface. Tracheal muscle was smooth and lied internal to the open end of the hyaline cartilage.3. The CALT of the camel was formed by solitary or aggregate lymphoid nodule, few scattered lymphoid cells, which were mainly distributed in conjunctival fornix and third eyelid. The histological structure of lymphoid nodule was similar to NALT and LTALT. FAE consisted of flattened associated epithelial cells, M cells and intraepithelial lymphocytes. Few bacillar bacteria were occasional bound to the surface of CALT M cells in scatter or clusters. Regularly arranged microvilli on the surface of M cells with occasional shallow depression.Small vesicles occur beneath the outer cell membrane and inside the M cell. The germinal centre of the lymphoid follicles comprised of Lymphoblasts, follicular dendritic cells, few macrophages and plasma cells. The ultrastructure of FDC was similar to NALT and LTALT. Prominent lymph vessels were always present together with numerous HEV. Numerous vessels occurred in the PFA. B and T lymphocytes, macrophages were distributed in lymphoid nodule of CALT. The positive FDC were only found in germinal centres. These results suggested that CALT in the camel has the cytologic basis of normal mucosa reaction. As an active component of the EALT in the camel, the CALT were inductive sites for the common mucosal immune system as well as important components in ocular defense.