Populations of interacting immune systems: evolution and immunization

The acquired immune system of mammals (such as humans, mice, rats, and cattle) is the most studied immune system. Taking a quick look at the ‘tree of life’ reveals that this intensely studied system belongs to a very small minority of taxa, the jawed vertebrates, raising the question: why did this system evolve when all other plants and animals survive without it? This work reviews some of the ways in which immune systems may interact with each other in the context of evolution, and in terms of host immunization to pathogens.