External and Internal Defenses Immune System External and Internal Defenses

* Items described in last slide

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

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

I. Innate Immunity A) Phagocytic Cells B) antimicrobial proteins C) inflammatory response D) Systemic response

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

B) Antimicrobial Proteins 1) interferon ά and β secreted by virus-infected cells help neighboring cells inhibit viral reproduction 2) complement system = 30 serum proteins microbe presence triggers cascade cascade activates complement system system causes microbe to lyse also trigger inflammation (may also be activated by antibodies*)

C) Inflammation Triggered by chemical signals like histamine Complement system, allergen, antigen or injury cause mast cells to release histamine Histamine dilates capillaries, lets out more clotting elements, anti-microbial proteins Chemokines released by capillary attract phagocytes Clotting blocks spread of microbes

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

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

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

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

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

Antibodies Proteins secreted by differentiated B-cells (plasma cells) Bind to specific antigen Also called Immunoglobulins (Ig) 1) IgG – give passive immunity to fetus 2) IgA – in secretions, sweat, milk, tears 3) IgE – triggers histamines/ allergic rxns