Single cell transcriptome analysis of elephant leukocytes reveals a large number of monocytes in peripheral blood 2599

Abstract Description Both major species of elephants Loxodonta africana and Elephas maximus can live for more than 50 years in the wild and are listed as endangered species. Elephants have a unique leukocyte profile with approximately 50% of an individual’s leukocytes resembling monocytes. Such a high number of monocytes is more than other any other mammalian species, though there is debate as to the true identity of these cells. Why such high levels of monocytes are present and their function are unknown. Here we used single cell RNAseq to identify leukocyte populations from a captive Asian Elephant. Transcript sequences were compared to the African elephant genome, which is more highly annotated than the Asian elephant. Progressive uMAP analysis identified clusters of cells which corresponded to T cells, B cells, granulocytes, and monocytes. Importantly, the proportion of analyzed cells closely resembled the CBC counts from the same animal, indicating that our analysis could correctly distinguish cell types. We further restricted single cell transcriptome analysis of cells from myeloid origin, and, following exclusion of granulocytes, found that the remaining monocytes could be divided into four to six distinct subsets. Monocyte subsets were further analyzed by examining transcripts related to immune functions. These data confirm that elephants do in fact have a large population of monocytes in peripheral blood and will be useful in directing future studies to understand their function. Topic Categories Veterinary and Comparative Immunology (VET)