Differential white blood cell numbers in response to lipopolysaccharide exposure in marine and terrestrial mammals

Marine mammals, such as bottlenose dolphins ( Tursiops truncatus ) are often seen with wounds, bruises or shark bites down to the muscle, apparently with no signs of infection. In terrestrial mammals, including humans, similar injuries would be associated with infections, inflammation and potentially death. The objective of this study was to compare the differential leukocyte numbers in marine and terrestrial mammals under control conditions and following exposure to lipopolysaccharide (LPS). Blood samples were collected following routine procedures from healthy human anonymous volunteers from the blood bank at Instituto Mexicano del Seguro Social, La Paz, Baja California Sur, Mexico, and from healthy dolphins at CaboDolphin. All samples were taken with ethylenediaminetetraacetic acid (EDTA) as anticoagulant, transported to the laboratory on ice and processed within 24 h. Leukocytes were separated by centrifugation with ficoll hypaque and subjected to cell culture at 35°C with 5% CO 2 and constant humidity. Leukocytes (10 6 cells) from both species were exposed to 10 μg LPS μL − 1 for 24 or 48 h and number of each leukocyte cell type was registered; cell type was assigned based on morphological characteristics. Under control (no LPS) conditions, number of lymphocytes from both species was higher at 24 and 48 h as compared to the initial numbers. In humans, but not in dolphins, lymphocyte numbers were lower in cells exposed to LPS for 24 or 48 h as compared to untreated cells. In both species, at all times and regardless of exposure to LPS, an inverse relationship was observed between lymphocyte and neutrophil numbers. In humans, basophil number was lower in cells exposed to LPS for 24 and 48 h as compared to untreated cells. In T. truncatus only one cell with morphology similar to basophils was observed in only one individual. These differences in leukocyte types between species in response to LPS exposure could contribute to explain the apparent lack of infection or inflammation in injured marine mammals. This research was conducted in accordance with institutional ethical standards and following the 1964 Declaration of Helsinki and later amendments and in accordance with the FASEB Statement of Principles for the use of Animals in Research and Education. The research protocol (2018‐785‐010) was approved by the Ethics Committee of Instituto Mexicano del Seguro Social (CONBIOÉTICA‐09‐CEI‐009‐2016061). Support or Funding Information Consejo Nacional de Ciencia y Tecnología (CONACYT CB‐2016‐01‐283669)