Читать книгу Immunology - Richard Coico - Страница 82

As noted in Chapter 3, the complement system is a major component of innate immunity. Named for some of the earliest observations of its activity—a heat‐sensitive material in serum that “complemented” the ability of antibody to kill bacteria—we now know that complement comprises approximately 30 circulating and membrane‐expressed proteins. Complement components are mainly synthesized by liver hepatocytes and by cells involved in the inflammatory response. A list of the latter cell types and the complement components they produce is shown in Table 4.1.

The biological activities triggered by complement activation enhance pathways that remove microbial pathogens, and they also directly attack the pathogen itself. Because these activities are so powerful, however, they may also damage the host. Thus, under normal conditions, complement activation is tightly regulated. In this chapter we describe the different pathways of complement activation, complement’s key functions, and how complement activation is regulated. We also describe the clinical conditions that result from either inappropriate complement activation or deficiency of complement components.