Accessory spleen in cetaceans and its relevance as a secondary lymphoid organ

• Published in: Zoomorphology Vol. 133; no. 3; pp. 343 - 350
• Main Authors: e Silva, Fernanda Menezes de Oliveira, Carvalho, Vitor Luz, Guimarães, Juliana Plácido, Vergara-Parente, Jociery Einhardt, de Meirelles, Ana Carolina Oliveira, Marmontel, Miriam, Miglino, Maria Angelica
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2014; Springer Nature B.V
• Subjects: Adaptation; Animal Anatomy; Animal Systematics/Taxonomy/Biogeography; Animals; Biomedical and Life Sciences; Body organs; Body size; Cetacea; Coasts; Developmental Biology; Evolutionary Biology; Germinal centers; Histology; Immune system; Immunity; Life Sciences; Marine mammals; Medulla oblongata; Morphology; Organs; Original Paper; Spleen; Stomach; Stranding; Spleen; Lymphoid system; Cetacea; Immune system
• ISSN: 0720-213X; 1432-234X
• DOI: 10.1007/s00435-014-0223-x

The objective was to determine the prevalence of accessory spleens in cetaceans stranded on the north and northeastern coasts of Brazil and to describe their macroscopic and microscopic characteristics, thereby providing insights into the contribution of these structures to the immune system of cetaceans. Sixty-three Odontocetes and Mysticetes (total of 14 species), male and female, ranging from calves to adults, stranded from 2009 to 2013 on the Brazilian north and northeastern coasts, were evaluated. Accessory spleens were present in 38 animals (60.3 %), with 1–14 accessory spleens per animal. Their location varied among species, ranging from firmly adherent to the spleen, to the large curvature of the first stomach or both. The presence of these structures was apparently not related to age or sex. However, there was a higher prevalence in animals with a greater body size and known to make deeper dives. Both primary and accessory spleens had similar macroscopic morphology with no demarcation between cortex and medulla. Both primary and accessory spleens had similar histological characteristics. Furthermore, it was noteworthy that germinal centers became more discrete and reduced in number with increasing age. In conclusion, we inferred that accessory spleens may be an additional mechanism for adaptation to diving and that they have a complementary reservoir function and thus can be considered compensatory lymphoid organs to splenic activity.