Introduction to immunology Jan. 19 Reading: Chapter 1

Objectives Compare and contrast the general functions of different types of immune cells Summarize the roles of: –innate versus adapative immunity –cellular versus humoral immunity

History of immunology Early observers noticed that survivors of certain diseases were resistant to re-infection Mary Wortley Montagu Excerpt from a letter by M. W. Montagu, 1717: “….The old woman comes with a nutshell full of the matter of the best sort of smallpox and asks what veins you please to have opened. She… puts into the vein as much venom as can lie upon the head of her needle. …You may believe I am very well satisfied of the safety of the experiment since I intend to try it on my dear little son. …I should not fail to write to some of our doctors very particularly about it if I knew any one of 'em that I thought had virtue enough to destroy such a considerable branch of their revenue for the good of mankind….”

History of immunology Edward Jenner, 1796 –1 st vaccinations: cowpox (vaccinia) Louis Pasteur, 1880s –Vaccines against cholera in chickens, rabies Emil von Behring & Shibasaburo Kitasato, 1890 –Serum from animals immune to diptheria or tetanus conferred immunity to recipients –“Antitoxic activity” = antibodies

History of immunology Eli Metchnikoff (shared Nobel Prize, 1908) –Phagocytic cells Paul Erlich (shared Nobel Prize, 1908) –Described different types of immune cells, antibodies

Components of the immune system Lymphoid cells –Lymphocytes Myeloid cells –Granulocytes –Monocytes/macrophages –Dendritic cells tology_mh/wbc1.html

Hematopoiesis

General functions of immune cells

Lymphocytes are small and inactive unless antigen recognition occurs General functions of immune cells

Primary lymphoid tissues Secondary (peripheral) lymphoid tissues Components of the immune system: Lymphoid tissues

Inflammation is triggered by infection

Lymphocytes encounter antigens in the peripheral lymphoid tissues

Two general types of immunity Innate (natural, native) Adaptive (specific, acquired)

Innate vs adaptive immunity Innate immunity Adaptive immunity Response time Number of specificities Specificity improves during response Memory responses

Innate immunity Phagocytes (macrophages, neutrophils, dendritic cells) –Engulf microbes or foreign particles –Release proinflammatory cytokines, chemokines Complement Inflammation (early) Antigen processing and presentation

Antigen presentation T cell receptors cannot bind antigens in the native state Must be processed and presented on an MHC protein Antigen presenting cells (APCs) –Crucial bridge between innate and adaptive immunity

Adaptive immunity APCs required Lymphocytes activated Effector mechanisms respond to different types of pathogens –Humoral (B cells, antibodies) –Cell-mediated (T cells) Memory cells generated

Adaptive immunity Lymphocyte activation –Clonal selection and clonal expansion

Adaptive immunity: humoral responses

Cytotoxic T cells (CD8+, CTL) –Recognize antigens presented by MHC I –Response to cytosolic pathogens –Directly lyse target cells Adaptive immunity: cell-mediated immunity

Helper T cells (CD4+) –Recognize antigens presented by MHC II –Response to extracellular pathogens –3 major classes: T H 1 T H 2 Regulatory T cells –Boost proliferation and function of other immune cells Adaptive immunity: cell-mediated immunity

Immune-related diseases