ABSTRACT
This chapter discusses the specific immune effector mechanisms that are responsible for host defense against infection with pathogenic bacteria, viruses, protozoa, and worms. Effector mechanisms mediated directly by antibody will be described first, followed by effector mechanisms mediated by antibody indirectly through the activation of the complement and phagocytic systems. The receptors for the Fc portion of antibody and the receptors for complement products function similarly on macrophages and neutrophils. The classical pathway of complement activation was probably superimposed on the alternative pathway of activation with the result that the functions of the complement system were coordinated with the actions of the antibody system. The first step in activation of complement by the classical pathway is binding of C1 Fc receptors to two or more IgG antibody molecules. The binding of antibody to a microbial surface will cause the deposition and serial activation of complement proteins.
