Phagocytic Function and Flow Cytometric Phenotype of Asian Elephant Monocytes

Optimal veterinary care of managed elephant populations is vital due to the continued decline of wild populations. Appropriate health monitoring and accurate disease diagnosis include hematologic evaluation. Elephant hematology is distinctive in that elephants have high percentages of monocytes in health. Elephant monocytes also have unusual morphology, a feature shared with manatees and rock hyraxes. Manual white blood cell counting is used for elephant hematology, as analyzers are generally inaccurate. The aims of this study were to evaluate basic cell isolation and functional testing protocols for use in elephant monocyte research, and to test several available antibodies via flow cytometry for use in elephant monocyte identification. Peripheral blood samples from five Asian elephants (Elephas maximus) were used. Methods for monocyte isolation and evaluation of phagocytic function were established. Putative lymphocyte and monocyte populations were identified using a scatter on flow cytometry. Antibodies against CD11b, CD11c, CD14, and ionized calcium-binding adapter molecule 1 (IBA1) were tested, with IBA1 showing the highest apparent diagnostic utility in labeling monocytes. Combined flow cytometric scatter and IBA1 positivity appear to identify Asian elephant monocytes. These data provide a methodologic basis for further investigation into elephant monocyte function and immune response to infection.