Aims State the normal functions of the immune system. State the primary and secondary lymphoid tissues and their functions. Readings: Abbas & Lichtman, Chapter 1

Immunity From the Latin immunis meaning exempt Immunity refers to all the mechanisms used by the body as protection against foreign environmental agents

Normal Functions of the Immune System Protect from infectious disease or re-infection Prevent entry/access of microorganisms Prevent or inhibit growth of microorganisms (Fe++) Neutralize toxins Kill or destroy infectious agents Sequesters (‘walls-off’) infectious agents Removes effected cells and cellular debris Surveillance for neoplastic cells

Normal Functions of Immune System The physiologic function of the immune system is to prevent infections and eradicate established infections. AIDS has demonstrated how important the immune system really is. Abbas & Lichtman’s Basic Immunology 1-1

Normal Functions of Immune System Vaccinations are effective because they stimulate an immune response to microbes and prime the immune system for a potential infection by that microbe. Vaccines have eradicated certain infectious diseases. Abbas & Lichtman’s Basic Immunology 1-2

Vaccines Are vaccines safe? - the pertussis paradigm 2 children die in Japan soon after receiving the whole cell pertussis vaccine in 1974. That year there were no deaths related to pertussis. 1974 - 1979 there was a >1300% increase in pertussis cases. In 1979, 41 children died of pertussis in Japan. An acellular pertussis vaccine now exists which has eliminated the alleged offending antigen.

Vaccines Are vaccines safe? - the MMR vaccine Finnish study from 1982 - 1996. 1.8 million individuals vaccinated with 3 million vaccine doses. 173 potentially serious reactions, with 1 death. 77 neurologic 73 allergic 22 miscellaneous 3.2 serious events per 100,000 vaccines administered.

Vaccines Why vaccinate?

Normal Functions of the Immune System The majority of microorganisms that are encountered are destroyed quickly by the innate (non-specific) immune system these do not induce an adaptive (specific) immune response Immune specificity – cells that are capable of attacking influenza virus are not necessarily adept at killing streptococcal bacteria

Abnormal Functions of the Immune System Autoimmunity – immune reaction to self Immune pathology – often a consequence of the immune response Collateral damage pathology Hypersensitivities Immune deficiencies

Cells and Tissues of the Immune System The major players are the leukocytes (WBCs) Primary lymphoid tissues give rise to leukocytes Bone marrow major site of leukocyte, erythrocyte (red blood cell) and platelet development all bone marrow-derived cells arise from a pluripotent stem cell Thymus encapsulated organ lying anterior to the heart within the rib cage site of further maturation by a select group of bone marrow cells – T-lymphocytes haemopoiesis <haematology> The formation and development of blood cells involving both proliferation and differentiation from stem cells. In adult mammals usually occurs in bone marrow. Haemo = blood; Poiesis = producing or give rise to; Pluripotent = not fixed in regards to its developmental potential thymus <anatomy> The lymphoid organ in which T lymphocytes are educated, mature and multiply. It is composed of stroma (thymic epithelium) and lymphocytes, almost entirely of the T-cell lineage. In mammals the thymus is just anterior (in front of) to the heart within the rib cage, in other vertebrates in rather undefined regions of the neck or within the gill chamber in teleost fish. The thymus regresses as the animal matures. – “It’s all down hill after puberty” (the thymus grows through puberty and then atrophys the rest of your life). If you take the thymus out of a fetal mouse – it develops a potentially lethal wasting disease. But if you remove the thymus from an adult mouse – when T cells have already populate the secondary lymphoid organs – not much happens (unless you remove the peripheral T cells with something like whole-body irradiation).

Cells of the Immune System Abbas & Lichtman’s Basic Immunology 1-11

Maturation of Lymphocytes Lymph nodes Spleen Mucosal and Cutaneous Lymph tissue Bone Marrow Blood Stem Cell Blood, Lymph Thymus Lymphocytes develop from precursors in the generative (1) lymphoid organs. Bone marrow for B lymphocytes Thymus for T lymphocytes Abbas & Lichtman’s Basic Immunology 1-12

Maturation of Lymphocytes Mature lymphocytes enter the peripheral lymphoid organs (lymph nodes, spleen, & other lymphoid tissues) where they respond to foreign antigens and recirculate into the blood and lymph. These locations are the 2 lymphoid tissues Here, lymphocytes can interact with other leukocytes and undergo differentiation haemopoiesis <haematology> The formation and development of blood cells involving both proliferation and differentiation from stem cells. In adult mammals usually occurs in bone marrow. Haemo = blood; Poiesis = producing or give rise to; Pluripotent = not fixed in regards to its developmental potential thymus <anatomy> The lymphoid organ in which T lymphocytes are educated, mature and multiply. It is composed of stroma (thymic epithelium) and lymphocytes, almost entirely of the T-cell lineage. In mammals the thymus is just anterior (in front of) to the heart within the rib cage, in other vertebrates in rather undefined regions of the neck or within the gill chamber in teleost fish. The thymus regresses as the animal matures. – “It’s all down hill after adolescence”

Maturation of Lymphocytes Lymph nodes Spleen Mucosal and Cutaneous Lymph tissue Bone Marrow Blood Stem Cell Blood, Lymph Thymus Abbas & Lichtman’s Basic Immunology 1-12

Secondary (2o) Lymphoid Tissues Lymph nodes Spleen Mucosa-associated lymphoid tissue (MALT) Pharyngeal tonsils Peyer’s patches lung lamina propria of GI tract Roitt’s Immunology 7-2