CHAPTER 31 Summary

• The immune system defends the body against infection by pathogens.
• Pathogens are infectious agents that cause an immune response; they include certain bacteria, viruses, fungi, and parasites.
• Viruses are acellular; they consist of a genome of nucleic acid (DNA or RNA) contained within a protein shell.
• The immune system has two main components: innate immunity and adaptive immunity. Innate immunity is the first defense against invaders; adaptive immunity comes into play once innate defenses are breached.
• The innate immune system includes defenses with which we are born, and which are always active: they include barriers such as skin and mucous membranes; antimicrobial chemicals in tears, saliva, and other secretions; and phagocytic cells that engulf and digest pathogens.
• The inflammatory response, part of the innate immune system, is triggered by tissue infection or injury. During an inflammatory response, blood vessels swell and leak, marshaling phagocytic cells and protective molecules to the area to contain the infection.
• Adaptive immunity is conferred by specialized lymphocytes called B and T cells.
• B cells produce antibodies that specifically recognize antigens on pathogens and mark the pathogens for destruction.
• T cells destroy infected, foreign, and cancer cells and stimulate B cells to produce antibodies.
• The immune response can go awry, causing allergies, which are responses to intrinsically harmless substances (for example, pollen), and autoimmune conditions that result when the immune system mounts a response against the body’s own cells and tissues.
• At the first exposure to a particular pathogen, a primary response is generated that takes time to become fully effective; the primary response also produces memory cells. Memory cells remain in the body and become active at the time of a subsequent exposure to the same pathogen, producing a more rapid and vigorous secondary response that fights the pathogen and usually prevents the associated illness.
• Vaccination elicits a primary response. Memory cells produced during the primary response protect against illness following subsequent exposure to the actual pathogen.
• The adaptive response is highly specific for particular pathogens. If the pathogen changes, by antigenic shift or drift, the body must mount a separate response for each strain of the pathogen.
• All organisms have ways of defending themselves against infection. The innate immune system is evolutionarily ancient.

• MORE TO EXPLORE

  • National Institute of Allergy and Infectious Diseases: Immune System www.niaid.nih.gov/topics/immunesystem
  • PBS, American Experience, Influenza 1918. www.pbs.org/wgbh/americanexperience/films/influenza/
  • Watanabe, T. (2009) Viral RNA polymerase complex promotes optimal growth of 1918 virus in the lower respiratory tract of ferrets. Proceedings of the National Academy of Sciences 106(2):587–591. www.pnas.org/content/106/2/588
  • Taubenberger, J., et al. (2007) Discovery and characterization of the 1918 pandemic influenza virus in historical context. Antiviral Therapy 12(4 Pt B):581–91. www.ncbi.nlm.nih.gov/pmc/articles/PMC2391305/
  • Barry, J. M. (2005) The Great Influenza: The Story of the Deadliest Pandemic in History. New York: Penguin Books.
  • Crosby, A. (2003) America’s Forgotten Pandemic: The Influenza of 1918. Cambridge, UK: Cambridge University Press.