Background: Toxoplasma gondii (T. gondii) was 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.
Methods: 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. The transcriptional levels of virulence factors ROP18, ROP16, and MIC3 were calculated using the real-time PCR method to determine whether T. gondii virulence was reduced when co-cultured with chicken erythrocytes.
Results: We discovered that T. gondii can adhere to but not invade chicken erythrocytes and eventually cause apoptosis in chicken erythrocytes. When tachyzoites were co-cultured 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 expressed and formed in the host-parasite junction. T. gondii RH 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 can attach to the surface of chicken erythrocytes, it’s unable to invade successfully, showing an inability to invade. Interestingly, we found that T. gondii secretome, lysates, and intact tachyzoites could cause apoptosis of chicken erythrocytes to varying degrees, which suggested a complex mechanism involved in the apoptosis of chicken erythrocytes induced by T. gondii.
Conclusions: This study elucidated that T. gondii can’t infect nucleated chicken erythrocytes and enriched our understanding of T. gondii's transmission mechanism among avian species.