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.
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.
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.
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
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