Читать книгу Immunology - Richard Coico - Страница 85

Antigen–antibody complexes are the major activators of the classical pathway, with antibody bound to the surface of a pathogen being the predominant example. Antibody synthesis in response to pathogens is the key characteristic of the adaptive, humoral immune response. Thus, the classical complement pathway is a major effector mechanism of the adaptive immune response and leads to the elimination of pathogens.

Soluble antigen–antibody complexes also activate the classical pathway. Although they are normally removed by macrophages, they are found in autoimmune conditions such as systemic lupus erythematosus (SLE), which we discuss later in the chapter (see also Chapter 12). Other activators of the classical pathway include some viruses (including HIV‐1, discussed later in this chapter), necrotic cells and subcellular membranes (e.g., from mitochondria), aggregated immunoglobulins, and β‐amyloid, found in Alzheimer’s disease plaques. C‐reactive protein (CRP)—a component of the inflammatory response (an “acute‐phase reactant”)—also activates the classical pathway; CRP binds to the polysaccharide phosphocholine that is part of the cell wall of many bacteria, such as Streptococcus pneumoniae.