AP Biology Immune System. Pathogens: agents that cause disease Immunity: the ability to avoid disease when invaded by a pathogen

Transcription

1 AP Bilgy Pathgens: agents that cause disease Immunity: the ability t avid disease when invaded by a pathgen Innate Immunity: nnspecific First line f defense Barriers such as skin Hard fr bacteria t penetrate Mlecules txic t invaders Stmach acid Nrmal flra bacteria and fungi that live n bdy surfaces Part f defense systems because they cmpete with pathgens fr nutrients and space Lyszyme: an enzyme that attacks bacterial cell walls; fund in tears, nasal mucus, and saliva Mucus traps micrrganisms s cilia can remve them Cilia cntinuusly mve the mucus plus debris upwards twards nse and muth. Cilia als sweep ut mucus trapped in respiratry system 2 nd line f innate defenses: meant t limit spread f invaders in advance f specific immune respnses Histamine: triggers enlargement f bld vessels (vasdilatin), which increases bld supply t the area and brings phagcytes. Respnsible fr symptms f cmmn cld, which are attempts t rid bdy f pathgens Prstaglandins: prmte bld flw t area Chemkines: attract phagcytes t area Pyrgens: increase bdy temperature t speed up immune system and make it mre difficult fr micrbes t functin Phagcytic cells, which ingest freign cells and ther particles. Use lyszymes Cmplement: lead t a bursting f invading cells These defenses may be present all the time r activated rapidly Adaptive Immunity: specific Distinguishes between substances prduced by self and nnself Invlves antibdy prteins and thers that bind t and destry pathgens Slw t develp and lng-lasting, fund nly in vertebrate animals B and T lymphcytes (arise frm stem cells in bne marrw) circulate the bld and recgnize different specific antigens Page 1 f 5

2 1. RECOGNITION antigen receptrs n B + T recgnize specific antigens (any substance that elicits an immune respnse frm B+T cells) by binding t them In rder t recgnize antigen it must be presented t B r T cell by antigenpresenting cell 2. ACTIVATION binding f antigen receptr activates B+T cells; they underg rapid cell divisin. The cells frm ppulatins f effectr cells and memry cells 3. EFFECTOR PHASE after being activated, B cells prduce antibdies; T cells engage in cell-mediated respnse T Cells Fight pathgens in cell-mediated respnse Activatin prcess begins when T cell antigen receptrs recgnize and bind t antigens that are displayed n surface f antigen-presenting cells (APCs) APCs can be macrphages, dendritic cells, and smetimes B cells Each T cell displays specificity fr ne particular epitpe (accessible piece f antigen) Once activated, T cells divide Sme becme effectr T cells The rest becme memry cells respnd t expsure f same antigen years later Respnsible fr immunlgical memry 2 types f T cells Helper T cells (aka CD4 cells) Activated by interactin with APC Annunce t immune system that freign antigens have entered bdy Trigger humral and cell-mediated respnses Activate ther helper T cells and Cyttxic T Cells Cyttxic T cells (aka CD8 cells) Attack and kill bdy cells infected with pathgens D this by cell-mediated respnse Activated cyttxic T cells prliferate int effectr cells and memry cells B Cells Antigen receptrs n surface t recgnize pathgens Different B cells have different antigen receptrs Prvide adaptive immunity thrugh humral respnse Prduce antibdies (immunglbins) Once activated, B cells secrete antibdies Once activated, B cells underg cell divisins t prduce effectr cells (plasma cells) that secrete antibdies, and memry cells, which are used t respnd t same antigen years later Page 2 f 5

3 Self-Tlerance Immune system nrmally exhibits self-tlerance, meaning it des nt attack bdy cells Smetime immature lymphcytes develp and have antigen receptrs fr bdy s wn cells; these cells attack bdy s cells Characteristic f autimmune disease If B and T cells are identified as self-reactive, they are destryed by apptsis Majr Histcmpatibility Cmplex (MHC) Mlecules Cllectin f cell surface markers that identify cells as self 2 main classes f MHC markers Class I MHC mlecules are fund n surfaces f every nucleated bdy cell Class II MHC mlecules are fund n specialized cells APCs: Antigen Presenting Cells Present an antigen r piece f antigen (epitpe) t immune system 1. APC takes in an antigen 2. APC either becmes infected with antigen f engulfs it 3. Enzymes break apart antigen int fragments within APC 4. Attach pieces f antigen t MHC mlecule 5. MHC mlecule mves t surface f cell and displays it 6. T and B cells becme activate if they can bind with expsed antigen Clnal Selectin Means by which ne particular lymphcyte that matches an antigen r epitpe is identified and activated Antigen presented t lymphcytes by APCs until a match is fund This triggers activatin f lymphcyte Lymphcyte divides rapidly, prducing shrt-lived effectr cells and lng-lasting memry cells Antibdies Aka immunglbins Used t identify and neutralize pathgens Grup f glbular prteins Y shaped Prduced by B cells Blueprints fr antibdies made early in life. When expsed t antigen, antibdies are chsen by clnal selectin Variety f antibdies is unlimited Page 3 f 5

4 Types f Immunity Passive Immunity Temprary Antibdies transferred t individual by smene else. Ex: maternal antibdies that pass t baby via placenta r breast milk. Ex: thse with weak immune systems might get injectins f gamma glbulin which are antibdies culled frm many peple. Used t bst weak immune system Active Immunity Permanent Individual makes wn antibdies after being ill and recvering r after being given an immunizatin/vaccine. A vaccine cntains dead r alive viruses t stimulate a full immune respnse and t impart lifelng immunity Bld ABO antibdies circulate in plasma f bld and bind t ABO antigens n surface f red bld cells Danger in transfusin if recipient has antibdies t the dnr s antigens Bld Type Antigens present n surface f red bld cells Antibdies present circulating in plasma A A B B B A O Nne A and B AB A and B Nne Bld type O is universal dnr because it has n bld cell antigens t be clumped by recipients bld AB is universal recipient because there are n antibdies t clump dnr s bld AIDs Acquired Immune Deficiency Disease Cllapsed immune system s thse with the disease are highly susceptible t disease, infectins, cancers, etc. Virus that causes AIDs is HIV (human immundeficiency virus), attacks cell that bear CD4 mlecules n surface, mainly Helper T cells HIV is a retrvirus; nce inside cell, it reverse transcribes itself and integrates newly frmed DNA int hst cell s genme Page 4 f 5

5 Overview f 1. Specificity: entire system depends n matching f antigens t antigen receptrs and matching f antigens t antibdies 2. Diversity: wide variety f different cell types defend bdy frm pathgens 3. Memry: B and T memry cells circulate fr a life-time 4. Capacity t Distinguish Self frm Nnself: ability f immune system t nt attack healthy bdy cells, knwn as self-tlerance Page 5 f 5