# Phagocytic Function and Flow Cytometric Phenotype of Asian Elephant Monocytes

## TL;DR

This study develops methods to identify and analyze monocytes in Asian elephants, which can improve disease diagnosis and immune research in these endangered animals.

## Contribution

The study introduces a flow cytometry method using IBA1 to identify Asian elephant monocytes, enabling more accurate immune cell analysis.

## Key findings

- IBA1 antibody showed the highest utility in labeling Asian elephant monocytes via flow cytometry.
- Monocyte isolation and phagocytic function evaluation methods were successfully established.
- Flow cytometric scatter combined with IBA1 positivity can identify elephant monocytes more accurately than microscopy.

## Abstract

All elephant species are now endangered or critically endangered. It is extremely important for the veterinary care of elephants to be effective at diagnosing diseases and monitoring treatment. Routine blood cell testing is a standard method for monitoring elephant health and detecting possible infections. Elephants naturally have different ratios of white blood cells (WBCs; immune cells) in their blood compared to other animals, with unusually high percentages of one cell type (monocytes). Because elephant WBCs also look different from those of most other animals, a person must identify the cells under the microscope instead of using machine analysis. These elephant-specific WBC features may be important in fighting diseases, but very little is known about elephant monocytes. The aims of this study were to establish methods for isolating elephant monocytes, studying their function, and accurately identifying them using flow cytometry, a more precise technique than microscopy. Blood from Asian elephants was used. Methods were created and tested. An approach to identifying elephant monocytes using flow cytometry was established. These results will lead to better studies of the elephant immune system and can help to more accurately count WBCs in elephant samples.

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.