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Characteristics of Adaptive Immunity

Antigenic specificity.

Diversity- can recognize > billion different antigens.

Specificity & Response increases & improves as it is being mounted.

Immunological Memory

Self vs nonself recognition.

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Specificity is achieved by Ig & the TCR.

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Functional gene composed to two or more gene segments joined together.

The diversity of the Ig & TCR is generated

by gene rearrangement.

A lymphocyte prior to development:

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B cells stimulated by antigen will have increased diversity through

somatic mutations.

Provides diversity & increases specificity of Ig!

Point mutations

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How does the immune response amplify & remain specific towards a pathogen?

Early theories:

Friedrich Breinl & Felix Haurowitz, 1930sInstructional Theory-

Paul Ehrlich, early 1900s:Selective theory: “Cells in the blood express side chain receptors that will react with infectious agents and inactivate them.” Kuby, Immunology

Macfarlane Burnet, 1950s:Further defined Ehrlichs selective theory into the clonal slection theory

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Clonal Selection Theory

Memory is achieved by the “memory cells”

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Fig. 1.15, Janeway (p. 16): The 4 basic principles of the clonal selection theory.

?

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How does the immune system prevent

recognition of self?

Tolerance: occurs in the primary lymphoid tissue by positive* & negative selection of lymphocytes.

Clonal DeletionAnergy

* Not shown

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Apoptosis:Protease (caspases)

are activated.

DNA degradation.

Nuclear membrane integrity compromised.

Organelle/cell shrinking.

Blebbing

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Kuby, Immunology

Apoptotic lymphocyteHealthy lymphocyte

How do B cells & T cells recognize & bind to antigen?

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bacterium

B cell

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APC

Antigen must be presented

to T-cells.

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Antigen Presentation to T-cells

MHC class I Expressed on all nucleated cells.

MHC class IIExpressed on Professional Antigen Presenting Cells (APCs):

MφDCB cells

Other cells types can be induced to express MHC II.

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Antigen must be processed to be displayed on MHC.

alpha betaalpha

B-2 microglobulin

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The Endogenous Pathway:MHC class IEndogenous Ag:

derived from pathogens that multiply intracellularly.

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Exogenous Pathway

MHC class IIExogenous antigen:

derived from pathogens that multiply outside of host cells or inside the phagolysosome.