To better understand the tissue organization of the cetacean immune system, lymphoid organs were collected from pantropical spotted (Stenella attenuata) and spinner (Stenella longirostris) dolphins incidentally killed in the yellow fin tuna fishery of the Eastern Tropical Pacific (ETP). A descriptive histological assessment of the spleen and lymph nodes was performed and it was found that the lymphoid organs exhibited the typical morphology of mammals with an intact immune system, with differences in tissue organization and composition between individual dolphins and among age groups (Romano et al. 2002). In order to provide quantitative data for this descriptive assessment, ImageJ software was used to measure the number and size of white pulp follicles in the spleen, marginal and mesenteric lymph nodes of each species. For the mature pantropical spotted dolphins, there was a significant decrease in spleen follicle size (F1,19 = 7.557, p = 0.013) and increase in number of follicles (F1,19 = 6.814, p = 0.017), but this pattern was not observed in spinner dolphins. There was also a significant negative correlation with age and splenic follicle size (r = – 0.475, p = 0.040), and a significant positive correlation with age and the number of splenic follicles (r = 0.546, p = 0.016) for spotted dolphins. Sex did not have a significant effect on spleen morphology for either species. There were significant negative correlations with age and the number of follicles in the marginal lymph nodes of spotted dolphins (r = – 0.825, p = 0.046), and the number of germinal centers in the mesenteric lymph nodes of spinner dolphins (r = – 0.827, p = 0.044). The number of lymph node follicles decreased with specimen body length (a proxy for age) for both species, but no significant correlation was found. These findings quantified descriptive findings from Romano et al. (2002) and suggest that age-related changes occur in the immune system of the pantropical spotted and spinner dolphins. Additional variables such as antigenic stimulation and individual immunologic state likely resulted in morphologic changes in the organs examined, which made it difficult to draw definitive conclusions regarding the effects of sex and sexual maturity.
Capuano, Alyssa, "Histological assessment of spleen and lymph nodes of the pantropical spotted dolphin (Stenella attenuata) and the spinner dolphin (Stenella longirostris): Age and sex differences" (2014). Internship Reports (Restricted). 126.
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