Research led by scientists from the Bellvitge Biomedical Research Institute (IDIBELL) and the Institute of Molecular Biology of Barcelona (IBMB) of the CSIC has managed to film how a few days-old embryos defend themselves from a potential infection by bacteria. The work is published this week in the journal Cell Host and Microbe.
Specifically, they have been able to see 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 carried out by white blood cells. Crucially, scientists could observe that this ability to eliminate bacteria is also present in human embryos.
Using state-of-the-art microscopy techniques, the research shows how cells capture Escherichia coli and Staphylococcus aureus bacteria through small protrusions of their membrane, in which the protein Actin is involved, as can be seen in the following images. From left to right: a zebrafish embryo with ingested Escherichia coli bacteria (epithelial cells appear blue and green; bacteria appear red and magenta); the surface of a human embryo with ingested Staphylococcus aureus bacteria (epithelial cells appear blue; bacteria appear magenta); a human embryo at the blastocyst stage, i.e., 5–6 days into development (epithelial cells thought to be capable of ingesting bacteria appear in blue). “Our research shows that, at the beginning of development – before implantation in the uterus and before the formation of organs – embryos already have a defense system that allows them to eliminate bacterial infections,” says Esteban Hoijman, researcher at IDIBELL and IBMB-CSIC, leader of the research. The first author of the work is Joan Roncero-Carol, a predoctoral researcher at the Embryonic Cell Bioimaging Laboratory at IDIBELL-CSIC.
This process, scientist explain, works as a phagocytosis mechanism, activates immunity genes in these cells, effectively eliminates bacteria and contributes to the correct embryonic development in case of infection.
“This system could represent the origin of immunity. The study reveals the first interaction between the newly forming organism and its biological microenvironment,” adds Hoijman, who heads the IDIBELL-CSIC Embryonic Cell Bioimaging laboratory.
Besides IDIBELL and CSIC, the research has involved scientists from the Centre for Genomic Regulation (CRG) from Barcelona, Pompeu Fabra University (UPF), the Institute for Bioengineering of Catalonia (IBEC), the University of Barcelona (UB), the Dexeus University Hospital and ICREA.
Preventing malformations and im
proving reproductive therapies
At the beginning of development, embryos are exposed to multiple changes in their environment which can pose a threat, since embryos have not yet developed the immune system to protect them.
In the uterus, infections have a high incidence and are associated with infertility. However, it has remained a mystery until now how an embryo reacts when it encounters a bacterium. This work reveals that immune capacities of an embryo begin long before the existence of white blood cells, and “could help us, in the future, to improve fertility, prevent embryonic malformations and develop new reproductive therapies,” explains Esteban Hoijman.
In this sense, the finding also highlights the important need to know in more detail the population of bacteria that can colonize the uterus, differentiating the invaders (and possible pathogens) from potential resident bacteria that could have beneficial effects on reproductive physiology.
The Bellvitge Biomedical Research Institute (IDIBELL) is a research center established in 2004 specialized in cancer, neuroscience, translational medicine, and regenerative medicine. It counts on a team of more than 1.500 professionals who, from 73 research groups, publish more than 1.400 scientific articles per year. IDIBELL is participated by the Bellvitge University Hospital and the Viladecans Hospital of the Catalan Institute of Health, the Catalan Institute of Oncology, the University of Barcelona, and the City Council of L’Hospitalet de Llobregat.
IDIBELL is a member of the Campus of International Excellence of the University of Barcelona HUBc and is part of the CERCA institution of the Generalitat de Catalunya. In 2009 it became one of the first five Spanish research centers accredited as a health research institute by the Carlos III Health Institute. In addition, it is part of the “HR Excellence in Research” program of the European Union and is a member of EATRIS and REGIC. Since 2018, IDIBELL has been an Accredited Center of the AECC Scientific Foundation (FCAECC).