Effects of Immune Selection on Population Structure of Bacteria

Abstract

Bacterial pathogens, the subject of this chapter, exhibit antigenic diversity both at the level of the pathogen population through allelic polymorphism and within individual bacteria, where the expression of antigenic loci may be switched on and off. The balance between the different effects of immune selection leads to the various patterns of antigenic diversity observed among bacterial pathogen populations. The chapter discusses some of these patterns and the theoretical frameworks that have been developed to try to understand them. The different population structures of meningococcal serogroups can be explained using simple mathematical models of immune selection. It introduces the basic frameworks used to understand the population dynamics of infectious diseases before describing models that incorporate pathogen population structure and the role of immune selection. For many bacterial pathogens, however, the immune response is generated to more than one antigen. Despite the complexity of the biological and epidemiological factors that affect the evolution of bacterial pathogens, a wide range of population structures can be accounted for using the simple theoretical models of immune selection. Understanding the role of immune selection for other bacterial pathogens will require similar large-scale projects that examine the structuring of antigenic determinants at a population level. As sequencing methods and other technological tools advance, examining pathogen population structures should become increasingly straightforward, enabling a deeper examination of the effects of immune selection on pathogen populations.