Adaptive immunity in jawed and jawless vertebrates
Although all animals have immune systems, only certain species have what is called adaptive immunity. Characterised by specificity and immunological memory, adaptive immunity is found exclusively in vertebrates. And while every vertebrate benefits from the long-term protection against disease that adaptive immunity provides, not all vertebrates have the same type of adaptive immune system. That’s because around 500 million years ago vertebrates split, evolving into two separate groups, each with its own form of adaptive immunity. “Whereas the immune systems in jawed vertebrates, a group that includes sharks and humans, are well characterised, much remains to be learned about adaptive immunity in jawless vertebrates such as lampreys and hagfishes,” says Thomas Boehm(opens in new window), a researcher at the Max Planck Institute for Biology(opens in new window) in Tübingen, Germany. With the support of the ImmUne project, Boehm set out to identify common design principles of adaptive immunity in both lineages of vertebrates while also highlighting critical differences. “In essence, our work looks to find the many roads to Rome,” adds Boehm. The project received funding from the European Research Council(opens in new window).
Shedding new light on the convergent evolution of vertebrates
Using genetic interference experiments in lampreys and by studying genetic complementation in mice, researchers were able to shed new light on the convergent evolution of vertebrates. For example, the project discovered that the key gene guiding the process for producing T-cells in the thymus, which play a vital role in defending against infections, is found in the immune systems of both the jawless lamprey and the jawed sister species. “This finding indicates that the primary lymphoid organs and lymphocyte lineages are a core element of adaptive immunity in vertebrates,” explains Boehm.
Finding similarities in the adaptive immune systems of vertebrates
Another area of similarity between the two branches of vertebrates is that both use the same enzymes (cytidine deaminases) to help form antigen receptors, the surface proteins that trigger the immune response. This points to the conclusion that gene conversion and not a recombination of genetic elements by other types of genome-editing enzymes represents the oldest evolutionary mechanism for the somatic diversification of antigen receptor genes. “Our work has provided unexpected insight into the evolutionary origin of the somatic diversification process of antigen receptor genes – arguably the most revolutionary aspect of vertebrate immunity,” notes Boehm.
Highlighting the value of comparative immunology
Although there were indications that the adaptive immune systems of jawed and jawless vertebrates may exhibit some similarities, the ImmUne project proved it. It also provided a foundation for future studies into the many variants of adaptive immunity that are being found in the more than 60 000 species of vertebrate – work that is enabling the discovery of shared components and the identification of species-specific solutions to immune defence. “Our results demonstrate the value of using comparative immunology to identify general properties of adaptive immunity and to ascertain the various routes nature has taken to achieve the same end,” concludes Boehm. “It also underscores the importance of preserving the diversity of living things, for it is clearly important, whether directly or indirectly, for human health and well-being.”
Keywords
ImmUne, adaptive immunity, vertebrates, jawed vertebrates, jawless vertebrates, immune systems, convergent evolution, comparative immunology
