Abstract
In this chapter, we will explain that B cells respond to antigen stimulation of their BCR with the production of antibodies. This is a key feature of the adaptive immune system and a major aim of vaccination. We will discuss the structure and function of BCRs and antibodies, in particular of their variable regions and their adaption to antigens, such as affinity maturation due to somatic hypermutations and isotype switching based on somatic recombination. In this context, we will present the different phases of the humoral response of B cells and their communication with T cells, in particular in germinal centers of lymph nodes. The effector functions of B cells will be discussed on the cellular level as well as in the context of BCR signaling.