The Immune System

Nonspecific vs. specific defenses Nonspecific defenses do not distinguish one infectious microbe from another Nonspecific defenses do not distinguish one infectious microbe from another Specific defenses recognize and defend against invading microbes and cancer cells Specific defenses recognize and defend against invading microbes and cancer cells

Nonspecific defenses Skin is a barrier that most bacteria and viruses can’t penetrate Skin is a barrier that most bacteria and viruses can’t penetrate Acids secreted by skin prohibit growth of many microbes Acids secreted by skin prohibit growth of many microbes Sweat, saliva, and tears contain enzymes that attack bacterial cell walls Sweat, saliva, and tears contain enzymes that attack bacterial cell walls Mucus produced in digestive and respiratory systems also protects against microbes Mucus produced in digestive and respiratory systems also protects against microbes

Nonspecific defenses Microbes that penetrate skin, digestive, or respiratory systems face neutrophils and monocytes Microbes that penetrate skin, digestive, or respiratory systems face neutrophils and monocytes macrophages that “eat” bacteria and viruses macrophages that “eat” bacteria and viruses Interferons and complement proteins attack microbes either directly or indirectly by impeding their reproduction Interferons and complement proteins attack microbes either directly or indirectly by impeding their reproduction

Nonspecific defenses Interferons are produced by infected cells Interferons are produced by infected cells Diffuse to healthy cells where they cause the cell to inhibit viral production Diffuse to healthy cells where they cause the cell to inhibit viral production Complement proteins are activated by microbes or immune system Complement proteins are activated by microbes or immune system Coat infected cells –easier to eat Coat infected cells –easier to eat Can amplify inflammatory response Can amplify inflammatory response

Nonspecific defenses: inflammatory response

Redness, heat, and swelling caused by Redness, heat, and swelling caused by Increase in blood flow, fluid, and cells Increase in blood flow, fluid, and cells Inflammatory response disinfects and cleans injured tissues Inflammatory response disinfects and cleans injured tissues Pus = dead white cells and fluid Pus = dead white cells and fluid Systemic response is widespread Systemic response is widespread Toxins or microorganisms released in bloodstream Toxins or microorganisms released in bloodstream Circulates through body Circulates through body

Nonspecific defenses: inflammatory response Systemic response cont’d. Systemic response cont’d. Inflammatory weapons: increase white blood cells, fever Inflammatory weapons: increase white blood cells, fever Low-grade fever can stimulate phagocytosis and inhibit growth of many microorganisms Low-grade fever can stimulate phagocytosis and inhibit growth of many microorganisms

Lymphatic system

Involved in both specific and nonspecific responses Involved in both specific and nonspecific responses Lymphatic system defenses occur in lymph nodes and lymphatic system organs Lymphatic system defenses occur in lymph nodes and lymphatic system organs Packed with lymphocytes and macrophages Packed with lymphocytes and macrophages Lymph carries microbes from infection sites and some cancer cells Lymph carries microbes from infection sites and some cancer cells In the lymphatic organs, macrophages may “eat” the invaders (nonspecific) In the lymphatic organs, macrophages may “eat” the invaders (nonspecific) Lymphocytes can be involved in specific immune response Lymphocytes can be involved in specific immune response

Specific immunity Often more effective than nonspecific response Often more effective than nonspecific response It also amplifies nonspecific response It also amplifies nonspecific response Specific response begins due to presence of an antigen Specific response begins due to presence of an antigen Can either increase number of cells that attack invader directly OR Can either increase number of cells that attack invader directly OR Produce antibodies Produce antibodies Immune system “remembers” antigens it has previously encountered Immune system “remembers” antigens it has previously encountered Responds immediately and vigorously Responds immediately and vigorously Is adaptive Is adaptive

Lymphocytes

Specific Immunity: Lymphocytes Humoral system defends against bacteria and viruses present in body fluids Humoral system defends against bacteria and viruses present in body fluids Fluids: blood, lymph, and interstitial fluid Fluids: blood, lymph, and interstitial fluid Antibodies, secreted by B cells and dissolved in the blood, are carried in lymph and blood to sites of infections Antibodies, secreted by B cells and dissolved in the blood, are carried in lymph and blood to sites of infections Cell-mediated immunity Cell-mediated immunity T-cells circulate in blood and lymph T-cells circulate in blood and lymph Attack body cells that have been infected Attack body cells that have been infected

Specific Immunity: Lymphocytes For BOTH humoral and cell-mediated immunity For BOTH humoral and cell-mediated immunity B & T cells have antigen receptors (antibodies) that protrude from cell surface B & T cells have antigen receptors (antibodies) that protrude from cell surface specific for one type of antigen** specific for one type of antigen** Each person has between 100 million to 100 billion different kinds of B & T cells! Each person has between 100 million to 100 billion different kinds of B & T cells!

Antigens Most antigens are molecules that are present on viral surfaces or foreign cells Most antigens are molecules that are present on viral surfaces or foreign cells B cells respond to free antigens in body fluid B cells respond to free antigens in body fluid Different antibodies can bind to the same antigen Different antibodies can bind to the same antigen

Specific immunity: clonal selection

Primary vs. Secondary immune response

Role of T cells in Immunity T cells battle pathogens that have already entered body cells T cells battle pathogens that have already entered body cells Respond to antigens that have bonded to body cell surfaces Respond to antigens that have bonded to body cell surfaces Mount cell-mediated defense and aid humoral immunity Mount cell-mediated defense and aid humoral immunity

T cells Cytotoxic T cells Cytotoxic T cells Only T cells that kill other cells Only T cells that kill other cells Synthesize a protein that ruptures infected cell Synthesize a protein that ruptures infected cell Helper T cells Helper T cells Secrete stimulatory proteins that help Secrete stimulatory proteins that help Promote production of more helper T cells and memory cells Promote production of more helper T cells and memory cells Activate cytotoxic T cells Activate cytotoxic T cells Stimulate B cells to produce antibodies Stimulate B cells to produce antibodies

Autoimmune Diseases MS: T cells attack myelin –a protein that insulates the axons of neurons (a brain thing) MS: T cells attack myelin –a protein that insulates the axons of neurons (a brain thing) Most common chronic neurological disease in developed countries Most common chronic neurological disease in developed countries

Immunodeficiency diseases SCID (Severe Combined Immunodeficiency): T and/or B cells are absent or inactive SCID (Severe Combined Immunodeficiency): T and/or B cells are absent or inactive “bubble” people “bubble” people

Allergies Stage 1Stage 2

HIV/AIDS HIV destroys the immune system by infecting helper T cells HIV destroys the immune system by infecting helper T cells Eventually develop AIDS Eventually develop AIDS Body cannot carry out cell-mediated or humoral response Body cannot carry out cell-mediated or humoral response Die from opportunistic infections Die from opportunistic infections 36.1 million people have HIV/AIDS 36.1 million people have HIV/AIDS 5.3 million new cases each year 5.3 million new cases each year