"Figure 1.21: This graph illustrates the primary and secondary immune responses related to antibody production after an initial and secondary exposure to an antigen. (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology. Figure 1.22: An antigen is a macromolecule that reacts with components of the immune system. (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology. Figure 1.23: A typical protein antigen has multiple epitopes, shown by the ability of three different antibodies to bind to different epitopes of the same antigen. (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology. Figure 1.24: The typical four-chain structure of a generic antibody monomer. Credit a: (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology. Credit b: modification of work by Tim Vickers. Public Domain. https://commons.wikimedia.org/wiki/File:Antibody_IgG2.png. Table 1.9: The five immunoglobulin (Ig) classes. (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology. Figure 1.25: Neutralization involves the binding of specific antibodies to antigens found on bacteria, viruses, and toxins, preventing them from attaching to target cells. (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology. Figure 1.26: Antibodies serve as opsonins and inhibit infection by tagging pathogens for destruction by macrophages, dendritic cells, and neutrophils. (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology. Figure 1.27: Antibodies, especially IgM antibodies, agglutinate bacteria by binding to epitopes on two or more bacteria simultaneously. (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology. Figure 1.28: In this example of ADCC, antibodies bind to a large pathogenic cell that is too big for phagocytosis and then bind to Fc receptors on the membrane of a natural killer cell. (c) Rice University. OpenStax Microbiology. CC BY 4.0. https://openstax.org/details/books/microbiology."