8536d_ch01_001-0238/1/02 4: 25 PM Page 1 mac79 Mac 79: 45_BW: Goldsby et al./ Immunology 5e Overview of the chapter 1 Immune system HE IMMUNE SYSTEM IS A REMARKABLY VERSATILE defense system that has evolved to protect animals from invading pathogenic microorganisms and cancer. It is able to generate an enormous variety of cells and molecules capable of specifically recognizing and eliminat ing an apparently limitless variety of foreign invaders. These cells and molecules act together in a dynamic network whose complexity rivals that of the nervous system Functionally, an immune response can be divided into two related activities-recognition and response. Immune Numerous T Lymphocytes Interacting with a Single Macrophage recognition is remarkable for its specificity. The immune system is able to recognize subtle chemical differences that distinguish one foreign pathogen from another. Further- a Historical Perspective more, the system is able to discriminate between foreign molecules and the body's own cells and proteins. Once a for s Innate Immunity ign organism has been recognized, the immune system a Adaptive Immunity recruits a variety of cells and molecules to mount an appro- priate response, called an effector response, to eliminate or s Comparative Immunity neutralize the organism. In this way the system is able to Immune Dysfunction and Its Consequences convert the initial recognition event into a variety of effector responses, each uniquely suited for eliminating a particular type of pathogen. Later exposure to the same foreign organ ism induces a memory response, characterized by a more rapid and heightened immune reaction that serves to elimi Like the later chapters covering basic topics in immu nate the pathogen and prevent disease nology, this one includes a section called"Clinical Focus This chapter introduces the study of immunology from that describes human disease and its relation to immu in historical perspective and presents a broad overview of These sections investigate the causes, consequences,or treat the cells and molecules that compose the immune system, ments of diseases rooted in impaired or hyperactive immune along with the mechanisms they use to protect the body function against foreign invaders. Evidence for the presence of very simple immune systems in certain invertebrate organisms then gives an evolutionary perspective on the mammalian Historical Perspective immune system, which is the major subject of this book. El ements of the primitive immune system persist in verte- The discipline of immunology grew out of the observation brates as innate immunity along with a more highly evolved that individuals who had recovered from certain infectious system of specific responses termed adaptive immunity. diseases were thereafter protected from the disease. The These two systems work in concert to provide a high degree Latin term immunis, meaning"exempt, "is the source of the of protection for vertebrate species. Finally, in some circum- English word immunity, meaning the state of protection stances, the immune system fails to act as protector because from infectious disease of some deficiency in its components; at other times, it be Perhaps the earliest written reference to the phenomenon comes an aggressor and turns its awesome powers against its of immunity can be traced back to Thucydides, the great his- own host. In this introductory chapter, our description of torian of the Peloponnesian War. In describing a plague in immunity is simplified to reveal the essential structures and Athens, he wrote in 430 BC that only those who had recov- function of the immune system. Substantive discussions, ex- ered from the plague could nurse the sick because the perimental approaches, and in-depth definitions are left to would not contract the disease a second time. Although early the chapters that follow societies recognized the phenomenon of immunity, almostchapter 1 ■ Historical Perspective ■ Innate Immunity ■ Adaptive Immunity ■ Comparative Immunity ■ Immune Dysfunction and Its Consequences Numerous T Lymphocytes Interacting with a Single Macrophage Overview of the Immune System T       defense system that has evolved to protect animals from invading pathogenic microorganisms and cancer. It is able to generate an enormous variety of cells and molecules capable of specifically recognizing and eliminat￾ing an apparently limitless variety of foreign invaders. These cells and molecules act together in a dynamic network whose complexity rivals that of the nervous system. Functionally, an immune response can be divided into two related activities—recognition and response. Immune recognition is remarkable for its specificity. The immune system is able to recognize subtle chemical differences that distinguish one foreign pathogen from another. Further￾more, the system is able to discriminate between foreign molecules and the body’s own cells and proteins. Once a for￾eign organism has been recognized, the immune system recruits a variety of cells and molecules to mount an appro￾priate response, called an effector response, to eliminate or neutralize the organism. In this way the system is able to convert the initial recognition event into a variety of effector responses, each uniquely suited for eliminating a particular type of pathogen. Later exposure to the same foreign organ￾ism induces a memory response, characterized by a more rapid and heightened immune reaction that serves to elimi￾nate the pathogen and prevent disease. This chapter introduces the study of immunology from an historical perspective and presents a broad overview of the cells and molecules that compose the immune system, along with the mechanisms they use to protect the body against foreign invaders. Evidence for the presence of very simple immune systems in certain invertebrate organisms then gives an evolutionary perspective on the mammalian immune system, which is the major subject of this book. El￾ements of the primitive immune system persist in verte￾brates as innate immunity along with a more highly evolved system of specific responses termed adaptive immunity. These two systems work in concert to provide a high degree of protection for vertebrate species. Finally, in some circum￾stances, the immune system fails to act as protector because of some deficiency in its components; at other times, it be￾comes an aggressor and turns its awesome powers against its own host. In this introductory chapter, our description of immunity is simplified to reveal the essential structures and function of the immune system. Substantive discussions, ex￾perimental approaches, and in-depth definitions are left to the chapters that follow. Like the later chapters covering basic topics in immu￾nology, this one includes a section called “Clinical Focus” that describes human disease and its relation to immunity. These sections investigate the causes, consequences, or treat￾ments of diseases rooted in impaired or hyperactive immune function. Historical Perspective The discipline of immunology grew out of the observation that individuals who had recovered from certain infectious diseases were thereafter protected from the disease. The Latin term immunis, meaning “exempt,” is the source of the English word immunity, meaning the state of protection from infectious disease. Perhaps the earliest written reference to the phenomenon of immunity can be traced back to Thucydides, the great his￾torian of the Peloponnesian War. In describing a plague in Athens, he wrote in 430 BC that only those who had recov￾ered from the plague could nurse the sick because they would not contract the disease a second time. Although early societies recognized the phenomenon of immunity, almost 8536d_ch01_001-023 8/1/02 4:25 PM Page 1 mac79 Mac 79:45_BW:Goldsby et al. / Immunology 5e: