Immune System Chapter 35 External and Internal Defenses

Phagocytic Cells = cells that engulf & digest antigens Antigens =any foreign molecule recognized by a lymphocyte (B or T cell) lymphocyte (B or T cell) a) most are proteins or polysaccharides a) most are proteins or polysaccharides b) may protrude from microbe membrane b) may protrude from microbe membrane c) epitope = tiny part the lymphocyte binds c) epitope = tiny part the lymphocyte binds

MHC = major histocompatibility complex Set of genes that code for MHC molecules All are cell surface proteins All are cell surface proteins Class I MHC display foreign peptides synthesized within the cell (cancer/virus) Class I MHC display foreign peptides synthesized within the cell (cancer/virus) found on most body cells found on most body cells Class II MHC display peptides broken off of microbes during phagocytosis Class II MHC display peptides broken off of microbes during phagocytosis found on phagocytic cells & B cells found on phagocytic cells & B cells

* Helper–T cells * Helper–T cells Type of T cell that binds to antigens displayed by phagocytic cells or B-cells Type of T cell that binds to antigens displayed by phagocytic cells or B-cells (Class II MHC molecules) (Class II MHC molecules) Helps promote acquired immune response Promote Humoral (B-cell) response by secreting cytokines Promote Humoral (B-cell) response by secreting cytokines Promote cell mediated-response (cytotoxic-T cells) Promote cell mediated-response (cytotoxic-T cells)

External Defenses 1) Skin…waterproof layer dead cells 1) Skin…waterproof layer dead cells 2) Linings of body tubes/cavities 2) Linings of body tubes/cavities a) sticky mucus w/ lysozyme enzymes a) sticky mucus w/ lysozyme enzymes b) ciliated cells in resp. tract b) ciliated cells in resp. tract c) stomach acid & bile salts c) stomach acid & bile salts d) urine & vaginal low pH d) urine & vaginal low pH 3) Neutral/beneficial bacteria population 3) Neutral/beneficial bacteria population

Internal Defenses I. innate immunity = present at birth, always present, all animals present at birth, always present, all animals II. aquired/adaptive immunity = activated by microbes/antigens activated by microbes/antigens a) Require self-recognition a) Require self-recognition (membrane proteins) (membrane proteins) b) only present in Vertebrates b) only present in Vertebrates

I. Innate Immunity

A) Phagocytic cells (4 types) 1) neutrophils – most abundant (1 st responders) 1) neutrophils – most abundant (1 st responders) 2) macrophages – largest 2) macrophages – largest 3) eosinophils – poison multi-cellular parasites 3) eosinophils – poison multi-cellular parasites 4) dentritic cells – activate acquired immunity 4) dentritic cells – activate acquired immunity a) digest pathogen into pieces a) digest pathogen into pieces b) bind pathogen pieces to MHC receptors* b) bind pathogen pieces to MHC receptors* c) display pathogen on cell membrane c) display pathogen on cell membrane d) attract helper T cells* d) attract helper T cells* e) helper T cells activate acquired imm. resp. e) helper T cells activate acquired imm. resp.

B) Natural Killer Cells NK cells vertebrate innate defense. NK cells vertebrate innate defense. Attack virus infected cells and cancer cells Attack virus infected cells and cancer cells NOT MHC molecule receptors…just detects changes in cell membrane NOT MHC molecule receptors…just detects changes in cell membrane Produce signal molecules that cause apoptosis Produce signal molecules that cause apoptosis

C) Antimicrobial Proteins 1) interferon ά and β 1) interferon ά and β secreted by virus-infected cells secreted by virus-infected cells help neighboring cells inhibit viral reproduction help neighboring cells inhibit viral reproduction 2) complement system = 30 serum proteins 2) complement system = 30 serum proteins a. microbe presence activates complement proteins a. microbe presence activates complement proteins b. cascade of chem rxns lead to b. cascade of chem rxns lead to c. microbe lysis c. microbe lysis d. plays a role in inflammation d. plays a role in inflammation (complement syst also activated by acquired response)

D) Inflammation Triggered by chem. signals: histamine & cytokine Complement system, allergen, antigen or injury cause mast cells to release histamine Complement system, allergen, antigen or injury cause mast cells to release histamine Histamine dilates capillaries, lets out more clotting elements, anti-microbial proteins Histamine dilates capillaries, lets out more clotting elements, anti-microbial proteins Chemokines released by capillary attract phagocytes (macrophages & neutrophiles) Chemokines released by capillary attract phagocytes (macrophages & neutrophiles) Macrophages secrete cytokines that promote blood flow Macrophages secrete cytokines that promote blood flow Clotting blocks spread of microbes Clotting blocks spread of microbes

Signal Molecules Review Histamines –released by mast cells Histamines –released by mast cells - trigger capillaries to dilate - trigger capillaries to dilate Chemokines – released by capillaries Chemokines – released by capillaries - attract phagocytes - attract phagocytes Cytokines -released by macrophage/neutrophils Cytokines -released by macrophage/neutrophils - increase blood flow - increase blood flow -released by helper T -released by helper T - activate acquired immune resp. - activate acquired immune resp. signal B-cells and cytotoxic-T cells signal B-cells and cytotoxic-T cells

E) Systemic Response Widespread response Widespread response Increased WBC production Increased WBC production Fever – facilitates phagocytosis Fever – facilitates phagocytosis Septic shock – bacterial infection causes high fever low bp may cause death Septic shock – bacterial infection causes high fever low bp may cause death

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II aquired/adaptive immunity A) Humoral Response = A) Humoral Response = B cells make antibodies B cells make antibodies B) Cell Mediated Response = B) Cell Mediated Response = Cytotoxic T cells defends against: Cytotoxic T cells defends against: infected cells infected cells Cancer cells Cancer cells Transplanted cells Transplanted cells

Antibodies Proteins secreted by differentiated B-cells Proteins secreted by differentiated B-cells (plasma cells) (plasma cells) Bind to specific antigen Bind to specific antigen Also called Immunoglobulins (Ig) Also called Immunoglobulins (Ig)

Humoral Response = B cells put antibodies in fluid (humor) 1. B cell receptor binds to an antigen on microbe, pollen or transplanted cell 1. B cell receptor binds to an antigen on microbe, pollen or transplanted cell 2. B cell takes in antigen and presents it on MHC II surface protein to attract helper T cells 2. B cell takes in antigen and presents it on MHC II surface protein to attract helper T cells 3. Helper T binds to MHC-antigen complex and begins secreting cytokines 3. Helper T binds to MHC-antigen complex and begins secreting cytokines 4. cytokines induce mitosis in B cell to produce 4. cytokines induce mitosis in B cell to produce a. plasma cells a. plasma cells b. memory B-cells b. memory B-cells

Plasma cells make antibodies specific to the antigen that their parent B-cell bound Plasma cells make antibodies specific to the antigen that their parent B-cell bound antibodies antibodies 1.bind & clump viruses/bacteria 1.bind & clump viruses/bacteria 2. precipitate antigens dissolved in fluid 2. precipitate antigens dissolved in fluid 3. activate complement proteins 3. activate complement proteins Memory B-cells stay in blood stream ready to become activated in secondary immune response. Memory B-cells stay in blood stream ready to become activated in secondary immune response.

Secondary Immune Response

Cell Mediated Response =fights cancer, infected cells, transplant cells 1. Class I MHC molecule displays antigens 1. Class I MHC molecule displays antigens that are synthesized inside affected cell that are synthesized inside affected cell 2. Cytotoxic Tcells bind to MHC-antigen complex cell_activity_against_target_cells__quiz_1_.html 2. Cytotoxic Tcells bind to MHC-antigen complex cell_activity_against_target_cells__quiz_1_.html cell_activity_against_target_cells__quiz_1_.html cell_activity_against_target_cells__quiz_1_.html 3. Binding makes cytotoxic Tcell secrete: 3. Binding makes cytotoxic Tcell secrete: a. perforin a. perforin (protein, makes holes in membrane) (protein, makes holes in membrane) b. enzymes to digest the cell b. enzymes to digest the cell c. signals to cause apoptosis c. signals to cause apoptosis

More on Helper T Cells Helper T cells Activate by Helper T cells Activate by 1. binding C-II MHC-antigen complex 1. binding C-II MHC-antigen complex on dendritic cells, macrophages, or B-cells on dendritic cells, macrophages, or B-cells 2. Makes cytokines to stimulate 2. Makes cytokines to stimulate a. cytotoxic T cells to become active a. cytotoxic T cells to become active b. B cells to begin clonal selection….. b. B cells to begin clonal selection….. mitosis to produce plasma & memory cells mitosis to produce plasma & memory cells

Helper T clonal selection Activated helper T does mitosis Activated helper T does mitosis 1 clone divides to make many activated helper T cells 1 clone divides to make many activated helper T cells The other divides to make memory helper T cells The other divides to make memory helper T cells

Cell Types 1) Leukocytes = White Blood Cells 1) Leukocytes = White Blood Cells A) Lymphocytes (NK cells, B cells & T cells) A) Lymphocytes (NK cells, B cells & T cells) B) Phagocytes (eosinophils, neutrophils, B) Phagocytes (eosinophils, neutrophils, macrophages, dendritic cells) macrophages, dendritic cells) 2) Erythrocytes = Red Blood Cells 2) Erythrocytes = Red Blood Cells A) anucleate in mammals A) anucleate in mammals B) hemoglobin carries O 2 and some CO 2 B) hemoglobin carries O 2 and some CO 2 C) flexible biconcave oval C) flexible biconcave oval F) form in bone marrow F) form in bone marrow

Lymphocyte receptor diversity 1 million diff. B cells….10 million diff. T cells 1 million diff. B cells….10 million diff. T cells When leukocytes differentiate into lymphocytes When leukocytes differentiate into lymphocytes 1. Recombinase enzymes link 1 V gene 1. Recombinase enzymes link 1 V gene segment to 1 J gene segment segment to 1 J gene segment 2. all receptors on that cell the same 2. all receptors on that cell the same

Autoimmune disease New lymphocytes are tested to be sure their receptors won’t bind to bodies own cells. New lymphocytes are tested to be sure their receptors won’t bind to bodies own cells. Failure to remove self-reactive cells = autoimmune disease Failure to remove self-reactive cells = autoimmune disease