Evolution of Antigenic Variation

Abstract

processes that shape genetic variability and evolutionary change.The causes of variability and change provide the basis for understanding why simple vaccines work well against some viruses, whereas complex vaccine strategies achieve only limited success against other viruses.The battle between host and parasite often comes down to the rates at which attacker and defender molecules bind or evade each other. The biochemical details of binding and recognition set the rules of engagement that shape the pace, scale, and pattern of diversity and the nature of evolutionary change [45].The first section of this chapter lists the different ways in which parasites can gain by varying their antigenic molecules. The parasites may, for example, extend their time of infection within a particular host by changing their antigenic molecules to evade the specific recognition built up by the host immune system. Or the parasites may vary to attack hosts that had been exposed previously and had built up specific recognition against prior antigenic molecules.The second section focuses on the nature of binding and recognition between host and parasite molecules. I summarize the different ways in which parasites generate new variants in order to escape molecular recognition.The third section builds up the individual molecular interactions into the dynamics of a single infection within a host. The parasites spread in the host, triggering immune attack against dominant antigens.The battle within the host develops through changes in population numbers -the numbers of parasites with particular antigens and the numbers of immune cells that specifically bind to particular antigens.The fourth and fifth sections discuss how the successes and failures of different parasite antigens within each host determine the rise and fall of parasite variants over space and time. The distribution of parasite variants sets the immune memory profiles of different hosts, which in turn 225