The Novel Zoonotic Pathogen, <i>Anaplasma capra</i>, Infects Human Erythrocytes, HL-60, and TF-1 Cells <i>In Vitro</i>

• Main Authors: Yongshuai Peng, Chenyang Lu, Yaqun Yan, Jinxing Song, Zhiyang Pei, Pihong Gong, Rongjun Wang, Longxian Zhang, Fuchun Jian, Changshen Ning
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Pathogens
• Subjects: <i>Anaplasma capra</i>; zoonotic pathogen; erythrocyte; HL-60; TF-1
• Online Access: https://www.mdpi.com/2076-0817/10/5/600

<i>Anaplasma capra</i>, a species of the family Anaplasmataceae, is zoonotic tick-borne obligate intracellular bacteria. There have been no reports of human infection with this pathogen since 2015. Therefore, the zoonotic characteristics of <i>A. capra</i> need to be further studied. To verify the ability of <i>A. capra</i> to infect human cells, <i>A. capra</i> were inoculated in human erythrocytes, HL-60, and TF-1 cell lines <i>in vitro</i>. Cell smears were taken after inoculation, using Giemsa staining, transmission electron microscope (TEM), chromogenic in situ hybridization and immunocytochemistry for detection. In the Giemsa staining, many dark colored corpuscles or purple granules were seen in the inoculated erythrocytes, HL-60, and TF-1 cells. The results of chromogenic in situ hybridization show that there were brown precipitates on the surface of most erythrocytes. Immunocytochemistry results show many dark brown vacuolar structures or corpuscles in the cytoplasm of erythrocytes, HL-60, and TF-1 cell lines. The <i>A. capra</i> morulae were seen in the cytoplasm of both HL-60 and TF-1 in TEM, and their diameter was about 295–518 nm. Both dense-cored (DC) and reticulate cell (RC) form morulae could be seen. This study confirmed the ability of <i>A. capra</i> to infect human erythrocytes, HL-60, and TF-1. This study is of profound significance in further verifying the zoonotic characteristics of the pathogen and for establishing an <i>in vitro</i> cultivation model.