Immune Response: Introductory article Evolution Artice Contents Brief History of b Edwin LCooper,UCLA School of Medicine Los Angeles,,USA ertebrate Immune Response Phagocytosis in unicellular animals represents the most ancient and ubiquitous form of ogenitors of In defence against foreign material.Multicellular invertebrates and vertebrates possess Can we in phagocytic cells and have evolved more complexfunctions attributed to immuno-defence ne Systems cells that specialized into cellular and humoral immune responses. Brief History of Immunology Animals live successfully because they possess the full Self Versus Nonself capacity to function in a variety of ways.Living beings are anem rconizt tob an ite may occur ie re th organs of the digestive,endocrine.urinary.respiratory. reproductive and nervous systems.The immune system is autoimmune disease to develop so that an organism self- Cancer is considered to be one of the dreaded ats that to the death of an organism and and thei ducts tha encompass and protect the whole org ism against what developed next?In vertebrates,an antigen is simply potentially harmful pathogens(such as bacteria,viruses. the ligand of an antigen receptor generated by recombina parasites)that inhabit activator genes (RAG)and expressed only on xternal environment. ing to less re- ne inst threats(such as cancer) substances capable of stimulating an animal's immune ng of e wor system to respond by one of or a combination of esponses.pnagocy he more a me protects us from certain diseases.The earliest history trac immunology as a science to the microscope,which made it mediated by innate(or natural)responses as well as those and therefore any othe Edward Jenn nature ed t protected against e Invertebrate Immune Responses inoculated a small boy with pus from a cowpox sore and Around the and therefore could not speculate about the kinds of ice vac es s ha immune reactions that antigens or microbes could provoke virtually eradicated owins in the millions of vaccinations.What does this health orientation have to do withevolution ofimmunity?The answer liespartially in the time lef history of work on inverte react to foreign ma ng an showed us how to recognize the important role of cells in system. ENCYCLOPEDIA OF LIFE SCIENCES/2001 Nature Publishing Group/www.els.net 1 Immune Response: Evolution Edwin L Cooper, UCLA School of Medicine, Los Angeles, California, USA Phagocytosis in unicellular animals represents the most ancient and ubiquitous form of defence against foreign material. Multicellular invertebrates and vertebrates possess phagocytic cells and have evolved more complex functions attributed to immuno-defence cells that specialized into cellular and humoral immune responses. Brief History of Immunology Animals live successfully because they possess the full capacity to function in a variety of ways. Living beings are capable of eating, eliminating wastes, respiring, reprodu￾cing and responding to diverse environmental stimuli. The executors of these varied functions are the cells, tissues and organs of the digestive, endocrine, urinary, respiratory, reproductive and nervous systems. The immune system is likewise an indispensable organ system. In multicellular animals, immune systems contain different kinds of cells, tissues and organs and their molecular products that encompass and protect the whole organism against potentially harmful pathogens (such as bacteria, viruses, parasites) that inhabit the external environment. In fact, the immune system probably arose in evolution to defend organisms not only against external but also against internal pathological threats (such as cancer). Our current biological concept of immunity has changed considerably from the original meaning of the word. Quite literally, its earlier usage referred to exemption from military service or paying taxes. Now, an ‘immune system’ protects us from certain diseases. The earliest history traces immunology as a science to the microscope, which made it possible to identify at least one group of microorganisms – the bacteria – that cause disease. Just before the nineteenth century, Edward Jenner, an English country physician, reported the first successful attempt to prevent a disease by vaccination. His approach grew out of an observation of nature. Dairy maids and farmers often became infected accidentally with cowpox and later seemed to be auto￾matically protected against smallpox. Jenner deliberately inoculated a small boy with pus from a cowpox sore and found that the boy was immune to smallpox six weeks later. Later various modifications helped to produce vaccines so that smallpox and other infectious diseases are now virtually eradicated owing to the development and use of vaccinations. What does this health orientation have to do with evolution of immunity? The answer lies partially in the history of work on invertebrate immunity and how all animals react to foreign material by having an immune system. Self Versus Nonself The immune system recognizes the differences between ‘self’ and ‘not self’ in its attempt to maintain a balanced internal milieu, but the distinction is not rigid as the opposite may occur – i.e. reactions to self may cause autoimmune disease to develop so that an organism self￾destructs. Cancer is considered to be one of the dreaded internal threats that can lead to the death of an organism. Now that we have the rudiments of an immune system, what developed next? In vertebrates, an antigen is simply the ligand of an antigen receptor generated by recombina￾tion activator genes (RAG) and expressed only on vertebrate lymphocytes. According to another, less re￾stricted definition, perhaps more applicable to inverte￾brates, antigens are any multitude of various chemical substances capable of stimulating an animal’s immune system to respond by one of or a combination of several responses: phagocytosis; the more advanced cell-mediated immune response; or the even more complicated synthesis and secretion of antibody. The first two responses may be mediated by innate (or natural) responses as well as those generated by reactions to antigen receptors. Our own body components are integral to self and therefore any other components are not self. Invertebrate Immune Responses Around the end of the nineteenth century we knew essentially nothing about invertebrate immune responses and therefore could not speculate about the kinds of immune reactions that antigens or microbes could provoke in the millions of animals that inhabit the earth. Metchnik￾off, a Russian biologist who worked at the Pasteur Institute in Paris, broke this impasse and at the same time left the scientific world with two essential legacies. First, he clearly showed us how to recognize the important role of cells in effecting immune reactions, thus shattering the monolithic view of immunology that was essentially humoral in its Article Contents Introductory article . Brief History of Immunology . Self Versus Nonself . Invertebrate Immune Responses . Progenitors of Immunocytes . Can We Compare Vertebrate and Invertebrate Immune Responses? From Eating to Immunity . Vertebrate Immune Systems ENCYCLOPEDIA OF LIFE SCIENCES / & 2001 Nature Publishing Group / www.els.net 1