Analysis of Zebrafish Innate Immunity Using Two Bacterial Species

Depending on the presence of an amniotic sac, which protects embryos from desiccation, vertebrates can be divided into two categories: amniotes, vertebrates with amniotic sacs, and anamniotes, vertebrates without amniotic sacs. As a result, anamniotes, which include the embryos of fish and amphibians, must develop in aquatic environments. In addition, due to the lack of an amniotic sac, which also serves as a barrier from the outside environment, anamniotes are more susceptible to bacterial infection at early stages than their amniotic counterparts. While it has been known that anamniotes possess immune systems similar to those of amniotes, it is still unclear how their immune systems fight against bacterial infection during early development. In this paper, I have examined how zebrafish embryos protect themselves from bacterial infection in order to understand the importance of the immune system during early development in anamniotes. My analysis shows that zebrafish embryos utilize phagocytic immune cells to suppress bacterial infection. Moreover, zebrafish embryos appear to be more vulnerable to infection by Gram negative than Gram positive bacteria, suggesting that the efficacy of phagocytic immune cells in anamniotes varies depending on the type of pathogen being fought against.