Porth's Pathophysiology, 9e

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UNIT IV Infection, Inflammation, and Immunity

Understanding

Innate and Adaptive Immunity

The body’s defense against microbes is mediated by two types of immunity: (1) innate immunity and (2) adaptive immunity. Both types of immunity are members of an integrated system in which numerous cells and molecules function cooperatively to protect the body against foreign invaders. The innate immune system stimulates adaptive immunity and influences the nature of the adap- tive immune responses to make them more effective. Although they use different mechanisms of pathogen recognition, both types of immunity use many of the same effector mechanisms, including destruction of the pathogen by phagocytosis and the complement system.

Innate Immunity Innate immunity (also called natural immunity ) consists of the cellular and biochemical defenses that are in place before an encounter with an infectious agent and provide rapid protection against infection. The major effector com- ponents of innate immunity include epithelial cells, which block the entry of infectious agents and secrete antimicro- bial enzymes, proteins, and peptides; phagocytic neutrophils and macrophages, which engulf and digest microbes; natural killer (NK) cells, which kill intracellular microbes and for- eign agents; and the complement system, which amplifies the inflammatory response and uses the membrane attack response to lyse microbes. The cells of the innate immune system also produce chemical messengers that stimulate and influence the adaptive immune response. The innate immune system uses pattern recognition receptors that recognize microbial structures ( e.g., sugars, lipid molecules, proteins) that are shared by microbes and are often necessary for their survival, but are not present on human cells. Thus, the innate immune system is able to dis- tinguish between self and nonself, but is unable to distin- guish between agents.

Microbe

Epithelial barriers

Monocyte/ macrophage Neutrophil

Phagocytosis

Cell death

NK cells

C5b

C6,C7,C8,C9

Membrane attack complex

Lysis of microbe

Complement