Abstract
In this chapter, we will learn that the major physiological function of the immune system is the protection of our body against microbe infections. First, we will summarize the principles of immune responses to control infections with all kinds of microbes. Then we will focus on the effector functions of humoral and cell-mediated innate and adaptive immunity against bacterial infections. Furthermore, we will discuss that an overreaction of the immune system to the presence of bacteria can lead to life-threatening sepsis. In addition, we will present emerging bacterial pathogens and discuss at the example of tuberculosis a more than 70,000 year-long interaction of Homo sapiens with Mycobacterium tuberculosis . Finally, we will explain the impact of the interaction of our immune system with the gut microbiome in the context of health and disease.