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Topics

Immunity

Lymphoid system

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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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Figure 16.1 – Humoral and cellular immunity

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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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Figure 16.2 – Anatomy of the lymphoid system

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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

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Primary Lymphoid Organs

Bone marrow – hematopoiesisboth B and T cells originateB cells mature in bone marrow

Thymusimmature T cells migrate to thymusT cells mature in thymus

Mature lymphocytes migrate to secondary lymphoid organswait to encounter antigen