Introduction to the Lymphatic and Immune System

Learning Objectives

  1. Identify the basic components of the lymphatic system and give their functions.
  2. Describe the basic function, locations and characteristics of the four types of lymphatic vessels.
  3. Describe the contents, production, flow and endpoint of lymph.
  4. Define lacteals and discuss their location and function.
  5. Describe the cellular structure, locations, and functions of diffuse lymphatic tissue and lymphoid follicles.
  6. Describe the structure, function, and major locations of lymph nodes.
  7. Describe the location, structure, and functions of the spleen.
  8. Describe the location, structure, age-related changes, and function of the thymus.
  9. Identify the three major tonsils and describe their locations and functions.
  10. Describe the location, function and structure of MALT, Peyer’s patches, and the appendix.
  11. Describe the components and characteristics of the innate immune system.
  12. Identify the physical characteristics of skin that make it a pathogen barrier.
  13. Provide examples of how the mucosae of each of the body’s tracts (digestive, respiratory, urinary, and reproductive) help limit pathogen entry and growth.
  14. Describe the mechanism of phagocytosis. Include the following terms in your discussion: adherence, opsonization, phagosome, lysosome, and enzymes.
  15. Describe the basic function of natural killer cells.
  16. Identify some basic triggers for the inflammatory response and the 4 cardinal signs of inflammation.
  17. Describe the production and basic function of interferons and complement proteins.
  18. Define fever and pyrogen and identify the benefits of a mild fever.
  19. Explain why adaptive immunity is specific, systemic, and exhibits memory. Contrast this with innate immunity.
  20. Describe the production and maturation process of T and B lymphocytes.
  21. Describe the activation, multiplication, and function of helper T lymphocytes.
  22. Describe the activation, multiplication, and function of B lymphocytes.
  23. Describe the basic structure and functions of antibodies.
  24. Describe the primary and secondary humoral immune responses. Indicate the typical lengths of the lag time and be able to graphically relate levels of plasma antibodies with time.
  25. Define active humoral immunity and differentiate between natural active humoral immunity and artificial active humoral immunity
  26. Define passive humoral immunity and differentiate between natural passive humoral immunity and artificial passive humoral immunity.
  27. Describe the activation, multiplication, and function of killer T lymphocytes.
  28. Describe the basic function of regulatory T cells.
The top panel shows a color-coded world map. The bottom panel shows many viruses on a cell.

Figure 1. (a) As of 2008, more than 15 percent of adults were infected with HIV in certain African countries. This grim picture had changed little by 2012. (b) In this scanning electron micrograph, HIV virions (green particles) are budding off the surface of a macrophage (pink structure). (credit b: C. Goldsmith)

In June 1981, the Centers for Disease Control and Prevention (CDC), in Atlanta, Georgia, published a report of an unusual cluster of five patients in Los Angeles, California. All five were diagnosed with a rare pneumonia caused by a fungus called Pneumocystis jirovecii (formerly known as Pneumocystis carinii).

Why was this unusual? Although commonly found in the lungs of healthy individuals, this fungus is an opportunistic pathogen that causes disease in individuals with suppressed or underdeveloped immune systems. The very young, whose immune systems have yet to mature, and the elderly, whose immune systems have declined with age, are particularly susceptible. The five patients from LA, though, were between 29 and 36 years of age and should have been in the prime of their lives, immunologically speaking. What could be going on?

A few days later, a cluster of eight cases was reported in New York City, also involving young patients, this time exhibiting a rare form of skin cancer known as Kaposi’s sarcoma. This cancer of the cells that line the blood and lymphatic vessels was previously observed as a relatively innocuous disease of the elderly. The disease that doctors saw in 1981 was frighteningly more severe, with multiple, fast-growing lesions that spread to all parts of the body, including the trunk and face. Could the immune systems of these young patients have been compromised in some way? Indeed, when they were tested, they exhibited extremely low numbers of a specific type of white blood cell in their bloodstreams, indicating that they had somehow lost a major part of the immune system.

Acquired immune deficiency syndrome, or AIDS, turned out to be a new disease caused by the previously unknown human immunodeficiency virus (HIV). Although nearly 100 percent fatal in those with active HIV infections in the early years, the development of anti-HIV drugs has transformed HIV infection into a chronic, manageable disease and not the certain death sentence it once was. One positive outcome resulting from the emergence of HIV disease was that the public’s attention became focused as never before on the importance of having a functional and healthy immune system.