Chapter 13
Innate and Adaptive Immunity
277
Cytokines and Their Role in Immunity
The ability of the cells of both the innate and adaptive
immune systems to communicate critical information with
each other by cell-to-cell contact and initiate end effector
responses is dependent upon the secretion of short-acting,
biologically active, soluble molecules called
cytokines
.
Cytokines are an essential component of host defense mech-
anisms and the primary means with which cells of innate
and adaptive immunity interact. Chemokines are a subset of
cytokines that consist of small protein molecules involved in
both immune and inflammatory responses.
2
They are respon-
sible for directing leukocyte migration to areas of injury and
to locations where primary immune responses are initiated
such as lymph nodes, the spleen, Peyer patches, and the ton-
sils.
2
The source and function of the main cytokines that par-
ticipate in innate and adaptive immunity are summarized in
Table 13.2.
General Properties of Cytokines
Cytokines are low molecular weight, regulatory, pro- or anti-
inflammatory proteins that are produced by cells of the innate
and adaptive immune systems and that mediate many of the
actions of these cells. The majority of the functionally impor-
tant cytokines are interleukins (ILs), interferons (IFNs), and
tumor necrosis factor alpha (TNF-
α
). Cytokines generate their
responses by binding to specific receptors on their target cells
and activating G-protein–coupled receptors.
2,3
Interleukins (ILs) are produced by macrophages and
lymphocytes in response to the presence of an invading micro-
organism or activation of the inflammatory process. Their pri-
mary function is to enhance the acquired immune response
through alteration of molecular expression, induction of leu-
kocyte maturation, enhanced leukocyte chemotaxis, and gen-
eral suppression or enhancement of the inflammatory process.
Immunity can be defined as the body’s ability to defend
against specific pathogens and/or foreign substances in
the initiation of disease processes. The multidimensional
response initiated by the body’s various defense systems is
known as the immune response. Some of these responses
become active almost immediately, while others develop
slowly over time. It is the coordinated interaction of these
mechanisms that allows the body to maintain normal inter-
nal homeostasis. However, when these mechanisms are
either depressed or overactive, they become responsible
for many of the pathophysiologic processes encountered in
health care.
Innate immunity and adaptive immunity are complemen-
tary processes that work to protect the body.
Innate immunity
,
the body’s first line of defense, occurs early and more rapidly
in response to foreign substances, while adaptive immunity
is usually delayed unless the host has been exposed before
(Table 13.1).
Intact innate immune mechanisms are essential for the
initiation of the adaptive immune response and, therefore,
a successful immune response dependent upon cooperation
between the two systems. Dendritic cells are an essential
component of both innate and adaptive immunity and serve
as the link between the two immune responses through the
release of dendritic cell–derived substances, such as cyto-
kines and chemokines.
1
As a result, innate immune cells are
capable of communicating important information regarding
key characteristics of the invading microorganism or foreign
substance to the B and T lymphocytes involved in adaptive
immunity. The adaptive immune response is also capable
of increasing its efficiency by recruitment and activation of
additional phagocytes and molecules of the innate immune
system. Each system is therefore essential for an effective
immune response and works in concert in the fight against
infection.
TABLE 13.1 FEATURES OF INNATE AND ADAPTIVE IMMUNITY
FEATURE
INNATE
ADAPTIVE
Time of response
Immediate (minutes/hours)
Dependent upon exposure (first: delayed, second:
immediate d/t production antibodies)
Diversity
Limited to classes or groups of microbes
Very large; specific for each unique antigen
Microbe recognition
General patterns on microbes;
nonspecific
Specific to individual microbes and antigens (antigen/
antibody complexes)
Nonself recognition
Yes
Yes
Response to repeated
infection
Similar with each exposure
Immunologic memory; more rapid and efficient with
subsequent exposure
Defense
Epithelium (skin, mucous membranes),
phagocytes, inflammation, fever
Cell killing; tagging of antigen by antibody for removal
Cellular components
Phagocytes (monocytes/macrophages,
neutrophils), NK cells, DCs
T and B lymphocytes, macrophages, DCs, NK cells
Molecular
components
Cytokines, complement proteins,
acute-phase proteins, soluble
mediators
Antibodies, cytokines, complement system
