Morphology of mucosa-associated lymphoid tissue in odontocetes

Abstract

This study describes the mucosa-associated lymphoid tissue (MALT) in odontocetes from the Brazilian coast and freshwater systems. Seven species were evaluated and tissue samples were analyzed by light, scanning and transmission electron microscopy, and immunohistochemistry. Laryngeal tonsil was a palpable oval mass located in the larynx, composed of a lymphoepithelial complex. Dense collections of lymphocytes were found in the skin of male fetus and calf. Clusters of lymphoid tissue were found in the uterine cervix of a reproductively active juvenile female and along the pulmonary artery of an adult female. Lymphoid tissues associated with the gastrointestinal tract were characterized by diffusely arranged or organized lymphocytes. The anal tonsil was composed of an aggregate of lymphoid tissue occurring exclusively in the anal canal, being composed of squamous epithelium branches. MALT was present in different tissues and organic systems of cetaceans, providing constant protection against mucosal pathogens present in their environment.

The Odontocete Ear Canal-Associated Lymphoid Tissue (ECALT) and Lymph Nodes: Morphological and Pathological Description with Immuno-Phenotypic Characterisation

“…The variation in cellular IR to anti-CD20 and other antibodies could be explained by cellular autolysis and the fixation of the tissue, associated with the time of fixation after death as well as the tissue type (e.g., the superficial tissue showed better fixation than the tissue at the level of the cartilage in all samples). The MALT in the skin of a foetus and juvenile Sotalia guianensis and a juvenile G. macrorhynchus appeared in clusters of T-cells ‘surrounded by B-cells’, showing a similar image to the single case of a bottlenose dolphin with active ECALT in our studies [ 11 ].…”

“…It was not organized as a well-defined structure or mass, but rather diffuse, making it part of the diffuse mucosa-associated lymphatic tissue (D-MALT). Lymphocytes associated with glandular structures occur in various cetacean mucosae such as the nasal sac system [ 25 ], the larynx [ 26 ], intestines [ 6 ], anus [ 27 ], and in the skin [ 11 ]. The lymphocytic populations in the connective tissue between the ear canal and cartilage, although here also considered to form part of the same ear canal-associated lymphoid tissue, were not spatially associated with glandular structures, but rather with vascular lacunae, indicative of an intricate relation with systemic functions.…”

“…Aside from nodular lymphoid tissue, several organs possess a mucosa-associated lymphoid tissue (MALT), which is diffusely spread lymphoid tissue along mucosal surfaces, essential in initiating an immune response to extraneous antigens [ 8 ]. In several species of small odontocetes, MALT sites have been determined including the organized tonsils in rrprthe larynx, spread clusters of lymphoid cells in the skin, uterine cervix, gastrointestinal tract, and the anal tonsil [ 7 , 9 , 10 , 11 ]. Although the odontocete MALT was concluded to be similar to the one in terrestrial mammals, the cellular composition is yet to be fully understood [ 11 ].…”

“…In several species of small odontocetes, MALT sites have been determined including the organized tonsils in rrprthe larynx, spread clusters of lymphoid cells in the skin, uterine cervix, gastrointestinal tract, and the anal tonsil [ 7 , 9 , 10 , 11 ]. Although the odontocete MALT was concluded to be similar to the one in terrestrial mammals, the cellular composition is yet to be fully understood [ 11 ]. For this purpose, immunohistochemical techniques for the cellular identification of lymphoid and antigen-presenting cells and macrophages have been successfully applied to a large variety of odontocetes, while there is still a large gap in knowledge on the immunological characteristics of the cetacean skin and annexes [ 4 , 11 , 12 , 13 , 14 , 15 ].…”

“…Although the odontocete MALT was concluded to be similar to the one in terrestrial mammals, the cellular composition is yet to be fully understood [ 11 ]. For this purpose, immunohistochemical techniques for the cellular identification of lymphoid and antigen-presenting cells and macrophages have been successfully applied to a large variety of odontocetes, while there is still a large gap in knowledge on the immunological characteristics of the cetacean skin and annexes [ 4 , 11 , 12 , 13 , 14 , 15 ].…”