Earliest Signs of Immune Response Found in Embryos

The fragile embryo deploys its own immune system to survive in its earliest days.

(CN) — Survival, if done right, can go completely unnoticed. A bird corrects its direction midflight to avoid a predator and an athlete stops to avoid being tackled or to catch a ball. These complex motions are done for survival, either instinctively or through force.

On a molecular level, the immune system fights infections and disease. But in the beginning, before any of that complex system develops, there is only the fragile embryo. And it must defend itself to survive.

In the first hours of development, the embryo mounts its own defense with the help of cells that act like a security system. These cells find, eat and destroy defective cells to help the embryo’s survival according to researchers from the Center for Genomic Regulation (CGR) in Barcelona, Spain, who report on this biological process in a study published Wednesday in the journal Nature.

This cycle occurs thanks to the arm-like protrusions on the surface of the epithelial cells. The dying cells are then eaten in a process known as phagocytosis, where a cell membrane devours particles for its survival.

Let’s rewind a moment to the first few hours of the embryo as it forms. Cell division begins and cellular errors can occur during this cycle due to environmental stress. Researchers say this is the cause of sporadic cell death and one of the major causes of an embryo not developing. Researchers used a four-dimensional imaging of a cell underdoing its development cycle.

A lot is riding on the safety of the embryo, but it is unable to develop its own specialized cells that make up the immune system. The question becomes whether embryos have a process for riding dying cells to improve its chance for survival.

Thanks to a high-resolution time lapse, a zebrafish and mouse embryo, researchers recorded the earliest tissues formed on the surface of embryo that act as the defense it needs to survive. This defense system is akin to a buffet.

“The cells cooperate mechanically; like people distributing food around the dining table before tucking into their meal, we found that epithelial cells push defective cells towards other epithelial cells, speeding up the removal of dying cells,” Dr. Esteban Hoijman, first and co-corresponding author of the paper, said in a statement.

In essence, the process plays out like a mechanical cooperation rather than the well-documented chemical process that happens between cells.

Dr. Verena Ruprecht with CRG and senior author of the paper said the research may have important applications to the study of screening methods used in fertility clinics.

“Here we propose a new evolutionarily conserved function for epithelia as efficient scavengers of dying cells in the earliest stages of vertebrate embryogenesis,” Ruprecht said in a statement.

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