Immune Response: Evolution

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, reproducing 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 automatically protected against smallpox. Jenner deliberately inoculated a small boy with pus from a cowpox sore and found that the boywas immune to smallpox sixweeks 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 evolutionof 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