Human Immune System Might Have Evolved From the Ancient Microbe ‘Asgard’

The immune system found in humans and all other complex life forms might have evolved from an ancient species of microbes known as Asgard archaea, as per new research. These microbes, believed to have emerged around 2 billion years ago, have provided insight into the origins of vital proteins that help organisms fend off viruses. According to the study led by Pedro Lopes Leão, a microbiologist at Radboud University, and Brett Baker, an associate professor at the University of Texas at Austin. The speculated discovery explains the evolution process of our immune system.

The Role of Asgard Archaea

The primary evolution of life is divided into three main domains: Bacteria, Eukarya, and Archaea. While bacteria are simple cells without a nucleus, eukaryotes have a more complex structure, housing their DNA in a nucleus and possessing specialised organelles. On the other hand, Archaea lack a nucleus but share energy-processing characteristics with eukaryotes.

Among archaea, the Asgard superfamily, discovered in 2015, plays a significant role in bridging the evolutionary gap between bacteria and eukaryotes, according to a Live Science report. These archaea were named after the realm of Norse gods due to their discovery near a hydrothermal vent in the Arctic Circle known as “Loki’s Castle.”

Immune Proteins with Ancient Origins

The study examined thousands of genomes across different life forms, identifying tens of thousands of viral defence systems. The researchers focused on two classes of proteins, viperins and argonautes, which are present across all domains of life. Viperins, part of the innate immune system in humans, combat viruses by preventing them from replicating within infected cells. Argonautes, initially found in plants, stop viruses from replicating by degrading their genetic material.

The findings, published in Nature Communications, indicate that the genes for these proteins are remarkably similar between archaea and eukaryotes, suggesting that they originated from a common Asgardian ancestor. The key catalytic sites of these proteins have remained largely unchanged over 2 billion years, indicating their effectiveness in defending against viral threats.