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Immunity
Matures throughout lifeHas memory – enhanced response to pathogensVaccination – deliberate exposure to pathogensMolecular specificityDiscriminates between self and foreignTolerance – ability to ignore given moleculesInformed by innate immune system
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Strategies of the Adaptive Immune System
Primary response – 1st response to an antigenrequires 1-2 weeksgenerates “memory” of effective mechanism
Secondary response – enhanced, antigen-specific“anamnistic response”consequence of memory
Two basic strategieshumoral immunity – extracellular antigenscellular immunity – intracellular antigens
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Humoral immunity
B lymphocytes (B cells)develop in bone marrowproliferate, differentiate into:
Plasma cellsantibody factoriesshort livedantibodies bind antigens, provide protection
Memory cells produced from some B cellslong livedrespond quickly upon reexposure to Ag
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Antibodies
Y – shaped molecules, two functional regionstwo identical arms bind antigen
highly specificaa sequences differ
stem recognized by other components
Protect by:direct mechanisms
coating inhibits pathogen bindingindirect mechanisms
stem facilitates phagocytosisAg-Ab stimulates complement
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B cell receptor
Membrane form of AbDifferent on different B cellsBinding to Ag causes B cell to multiplyB cell clones become plasma cells
secrete large amounts of specific Abrequires second signal from T helper cells
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Cellular Immunity
T lymphocytesT-cytotoxic cells – intracellular pathogensT-helper cells – orchestrate responses
T lymphocytes have T cell receptorfunctionally analogous to B cell receptorpermits recognition of specific antigen recognizes Ag presented on surface
of host cellsT cell clones differentiate into effector T cells
second signal provided by dendritic cellssome T cells form memory cells
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Lymphoid system
Lymphatic vessels carry lymphfluid extruded from oxygentated bloodprovides oxygen to tissuesmost reenters capillariesremainder enters lymphatics as lymph
Lymph may contain antigens from tissuestravels to lymph nodeslymph nodes remove protein and cellsprocessed lymph reenters circulation
Inflammation increase fluids, increasing lymphcarrying antigen from tissues
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Secondary Lymphoid OrgansSites where lymphocytes gather to contact AgLocated at strategic positions in bodyInclude:
lymph nodes – Ag from lymphaticsspleen – Ag from bloodtonsils – Ag from throatadenoids – Ag from throatappendix – Ag from intestine
Secondary lymphoid anatomy facilitates: cell interactionsinformation exchange via cytokinesmeeting place for lymphocytes,
dendritic cells and macrophagesswelling indicative of lymphocyte proliferation
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Other secondary lymphoid organs
Less organizedPeyer’s patches in small intestine
contain M cellscollect intestinal materialtransfer to lymphoid tissue below mucosa
MALT – mucosal-associated lymphoid tissueincludes Peyer’s patchesprovides “mucosal” immunityprevents organisms from entering
mucosal membranesSALT – skin-associated lymphoid tissue
collections of lymphocytes under the skin