Porth's Pathophysiology, 9e

Chapter 13 Innate and Adaptive Immunity    277

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) Very large; specific for each unique antigen Specific to individual microbes and antigens (antigen/­ antibody complexes) Immunologic memory; more rapid and efficient with subsequent exposure Cell killing; tagging of antigen by antibody for removal Yes

Diversity

Limited to classes or groups of microbes

Microbe recognition

General patterns on microbes; nonspecific

Nonself recognition Response to repeated infection

Yes

Similar with each exposure

Defense

Epithelium (skin, mucous membranes), phagocytes, inflammation, fever Phagocytes (monocytes/macrophages, ­neutrophils), NK cells, DCs Cytokines, complement proteins, ­acute-phase proteins, soluble mediators

Cellular components

T and B lymphocytes, macrophages, DCs, NK cells

Molecular

Antibodies, cytokines, complement system

components

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.