Zebrafish embryos can eliminate bacterial infections before forming their immune system

A group of researchers has managed to film how a few-day-old zebrafish embryo defends itself against a potential bacterial infection, reflecting its ability to eliminate bacterial infections before forming its immune system.

This is demonstrated by research led by the Barcelona Institute of Molecular Biology (IBMB) of the Spanish National Research Council (CSIC) and the Bellvitge Biomedical Research Institute (IDIBELL).

In the study, published in the journal Cell Host and Microbe , researchers have shown how zebrafish embryos use cells present on their surface, known as epithelial cells, to ingest and destroy bacteria through a process called phagocytosis , similar to that performed by white blood cells. The study also demonstrated that this ability to eliminate bacteria is also present in human embryos.

Using cutting-edge microscopy techniques, the research shows how cells capture bacteria such as Escherichia coli and Staphylococcus aureus through tiny protrusions in their membrane, which involve the protein actin.

"Our research shows that, at the beginning of development—before implantation in the uterus and before organ formation—embryos already have a defense system that allows them to eliminate bacterial infections," notes Esteban Hoijman, a researcher from IBMB-CSIC and IDIBELL and leader of the research.

This process, the research explains, functions as a phagocytosis mechanism, activates immune genes in these cells, effectively eliminates bacteria, and contributes to proper embryonic development in the event of infection. "This system could represent the origin of immunity. The study reveals the first interaction between the newly formed organism and its biological microenvironment," adds Hoijman, director of the Embryonic Cell Bioimaging Laboratory.

The research involved researchers from the Center for Genomic Regulation (CRG) in Barcelona, ​​Pompeu Fabra University (UPF), the Institute for Bioengineering of Catalonia (IBEC), the University of Barcelona (UB), Dexeus University Hospital, and ICREA.

Researchers explain that, at the beginning of development, embryos are exposed to multiple changes in their environment that can pose a threat, since they have not yet developed the immune system that protects them.

Infections in the uterus are highly prevalent and associated with infertility. However, until now, it was unknown how an embryo reacts when it encounters bacteria . This work reveals that an embryo's immune capabilities begin long before the existence of white blood cells, and "could help us in the future improve fertility, prevent embryonic malformations, and develop new reproductive therapies," explains Hoijman.

In this sense, the discovery also raises the need to understand in greater detail the population of bacteria that can colonize the uterus, differentiating between invaders (and potential pathogens) and potential resident bacteria that could have beneficial effects on reproductive physiology.