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Immunopharmacology concerns drugs that suppress, modulate, or stimulate immune functions (Figure 32–1). These agents include antibodies that have been developed for use in immune disorders. The drugs available comprise a wide variety of chemical and biopharmaceutical types. This chapter also describes the ways in which drugs activate the immune system and cause unwanted immunologic reactions.

Figure 32–1.

The initial division of drugs that affect the immune system is based on whether the drug suppresses or enhances immune function. Immune suppressants are divided into six classes. Immune potentiators are subsequently divided into three classes.

The innate immune system is the first line of defense against an antigenic insult and includes physical (e.g., skin), biochemical (e.g., complement, lysozyme, interferons), and cellular (e.g., neutrophils, monocytes, macrophages) components. The innate immune system initiates defense against pathogens and antigenic insult. The system thus involves the concerted actions of complement components, lysozymes, macrophages, and neutrophils (Figure 32–2). If the innate response is inadequate, the adaptive immune response is mobilized. This culminates in the activation of B and T lymphocytes. The cell types involved in immune responses can be identified by specific cell surface components or clusters of differentiation (CDs). Clusters of differentiation are molecules that can be used to characterize lymphocytes and other types of hematopoietic cells, including precursors of granulocytes, megakaryocytes, and erythrocytes. Thus a CD4 lymphocyte is one that carries the type 4 cluster of differentiation on its surface.

Figure 32–2.

Role of complement in innate immunity. Complement comprises nine proteins (C1–C9), which are split into fragments during activation. (a) Complement components (C3a, C5a) attract phagocytes (1) to inflammatory sites (2), where they ingest and degrade pathogens (3). (b) Complement components C5b, C6, C7, C8, and C9 associate to form a membrane attack complex (MAC) that lyses bacteria, causing their destruction. (c) Complement component C3b is an opsonin that coats bacteria (1) and facilitates their ingestion (2) and digestion (3) by phagocytes.

Antigen Recognition and Processing

This critical initial step in the adaptive immune response involves antigen-presenting cells (APCs). Dendritic and Langerhans cells, macrophages, and B lymphocytes are examples of APCs. These cells process antigens into small peptides that can be recognized by T-cell receptors (TCRs) on T helper (Th) cells (Figure 32–3). T helper cells are lymphoid cells derived from the thymus that mediate cellular immunity and can modify serologic immunity. The main subclasses of T cells are helper (CD4) cells and cytotoxic (CD8) cells.

Figure 32–3.

Scheme of cell-mediated and humoral immune responses. The cell-mediated arm of the immune response involves internalization and processing of antigen by APCs. The processed peptides bound to class II MHC surface proteins are ...

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