ABSTRACT
This chapter discusses the biochemical and biological consequences of the reaction between antigens (Ag) and antibodies (Ab). The Ag-Ab reaction involves specific sites in the antigen (epitopes) and antibody binding sites (paratopes). The Ag-Ab reaction is mediated by noncovalent bonds and is reversible. The fitness between the paratope and the epitope determines the affinity of the Ab, and in the case of complex antigens and multiple antibodies, the avidity. Cross-reactions result from an antibody paratope interacting with similar epitopes expressed by related or unrelated antigens. The Ag-Ab reaction can result in visible phenomena, such as protein precipitation and particle or cellular agglutination, but it also has significant biological consequences, including opsonization of microbes, neutralization of viruses, and complement fixation that is often associated with inflammatory reactions.
