Toxoplasma gondii adhesion and apoptosis of chicken erythrocytes

Toxoplasma gondii is thought to infect all nucleated cells in warm-blooded animals, including poultry, mammals, and humans. However, it is unclear whether T. gondii can infect chicken erythrocytes due to the nucleated nature of these cells. Due to the special role of chicken erythrocytes in innate immunity, we investigated the cell‒cell interaction between T. gondii and erythrocytes to elucidate the role of chicken erythrocytes in T. gondii infection. Cellular apoptosis was analyzed by transwell assay and flow cytometry. An immunofluorescence method was used to examine the reorganization of vimentin during T. gondii infection in both Vero cells and chicken erythrocytes. The reorganization of actin was evaluated to further examine the invasion capacity of tachyzoites on chicken erythrocytes during infection. We discovered that T. gondii can adhere to but not invade chicken erythrocytes and eventually cause apoptosis in chicken erythrocytes. When tachyzoites were cocultured with chicken erythrocytes in vitro, the transcriptional levels of T. gondii MIC3, ROP16, and ROP18 were significantly decreased. In addition, the rearrangement of host cell vimentin, a type III cytoskeleton protein regulated by T. gondii infection, was not observed. Similarly, the parasite-induced ring-shaped actin structure was not formed in the host-parasite junction. T. gondii (RH strain) tachyzoites preferentially invaded Vero cells and replicated in chicken blood monocytes, but they were not found in chicken erythrocytes. These findings showed that although T. gondii could attach to the surface of chicken erythrocytes, but couldn’t invade successfully. Interestingly, we found that the T. gondii secretome, lysates, and intact tachyzoites could cause apoptosis of chicken erythrocytes, which suggested a complex mechanism involved in the apoptosis of chicken erythrocytes induced by T. gondii. This study elucidated that T. gondii could not infect nucleated chicken erythrocytes and enriched our understanding of the transmission mechanism of T. gondii among avian species.