The Adaptive Immune System - An Overview

8/10/2019 The Adaptive Immune System - An Overview

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Dr. Fang-Ping Huang

Department of Pathology,

Immunology Division, Room 216Tel. 2855 4864

Email: [email protected]


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The immune system - an overview (basic concepts, features)

Developmental biology of the immune system (Dr. L. Lu)

Recent advances in lymphocyte lineage commitment (Dr. L. Lu) Apoptosis & the molecular cell death pathways (Dr. L. Lu)

Antigen recognition by T cells & its MHC restrictions

Pathways of antigen processing, presentation & co-stimulations Dendritic cells & the initiation of immune responses

Immune regulation & dys-regulation in health & in diseases

Essence and dvances in Contemporary Immunobiology


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Basic concepts in immunology Vaccination & the history of immunology

Types of immunity The adaptive immune system

Immunological specificity & memory B cells & humoral immune response T cells & cell-mediated immune response

The concepts of self/non-self & self -tolerance

The immune systeman overview


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Basic concepts in Immunology

Organisms and microorganisms Bacteria, viruses, fungi & parasites

Infections and diseasesInfection == disease

Mechanisms of defense The immune system

Cells & soluble factors

Immunity and Immunology


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Immunity

Original meaning: exemption from taxes

Other extended meaning: diplomatic immunity

In the context of Immunology: collective mechanisms against diseases


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Edward Jenner(1749-1823)

&The Discovery of

Vaccination (1796)

Vaccinia (cowpox)&

human smallpox


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Eradication of smallpox (1979, WHO)


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Vaccination

A process of induction of immunity to a pathogen by

deliberate injection of a weaken, modified or related form ofthe pathogen which is no longer pathogenic.


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Other historic events & important findings:

L. Pasteur (1880s) Vaccines against cholera, and rabies R. Kock (late 19th century)

Infections caused by microorganisms

P. Ehrlich et al. (1890s) Serum factors transfer of immunity

Behring & Kitasato (1890s) Antibodies in serum bound to pathogens

Porter & Edelman (1960s) Antibody structure

J. Gowans (1960s) Immunological importance of lymphocytes


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Size of the immune system?


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Dendritic cell(sentinel)


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Lymph Node


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The bursa of Fabricius in birds


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Cells, tissues and organs ofthe immune system

Immune cells are bone marrow-derived, & distributed through outthe body

Primary lymphoid organs: Thymus: T cell maturation Bone marrow (bursa of Fabricius in birds): B cell maturation

Secondary lymphoid organs: Lymph nodes Spleen Mucosal lymphoid tissues (lung, gut)


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Questions:

How may vaccines protect us from infections?

What may actually occur in our immune systemfollowing a vaccination?


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Types of immunity

Innate (natural) immunity Phagocytes etc.

Early, rapid responses, but limited &non-specifc

Adaptive (acquired) immunity Lymphocytes (B & T cells) Take time but powerful - specificity + memory


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Measles attacks & immunological memory


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Memory in adaptive immunity

1st infection memory 2nd infectionslow response fast response

pathogen proliferate pathogen killeddisease no diseasesymptoms no symptom


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Memory & specificity key features of the adaptive immunity


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Immunological memory & vaccination

Natural infections:1st infection memory 2nd infectionslow response fast response

pathogens multiply pathogens disposedSymptoms/disease no disease

Vaccination memory nature infectionsno disease fast response pathogens disposedno disease


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Vaccination protects us from infection byinducing the adaptive immune response, butbypassing the need for a primary infection


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Theoretical basis for immunologicalspecificity and memory

Theory of Clonal Selection Establishment of lymphocyte memory pool

Eh li h Sid h i H h i


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1 2

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Ehrlichs Side -chain Hypothesis (1900)


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Burnets Clonal Selection Theory Each lymphocyte produces one type of Ag receptors only, antigen selects and

stimulates cells carrying receptors specific for the antigen

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Immunological memory

The ability of the immune system to respond morerapidly and effectively to specific pathogens that havebeen encountered previously.

Reflection of the pre-existence of a clonally expandedpopulation (pool) of antigen specific lymphocytes.


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Humoral immune responses

B cells and antibodies

Cell mediated immune responses Cytotoxic T cell (Tc) Helper T cells (TH)

The adaptive immune mechanisms


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The Immune Recognition Molecules

of the Adaptive Immune System

1. Immunoglobulin (Ig)- B Cell Receptor (BCR)- Antibody (Ab)

2. T Cell Receptor (TCR)

3. Major Histocompatibility Complex (MHC)


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B Cellswork chiefly by secretingsoluble substances knownas antibodies (Ab)


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Ab basic structure

domains


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Ab V and C regions


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Neutralization: e.g. toxins, viruses

Opsonization: bind pathogens forrecognition by other immune cells

(e.g. phagocytes)

Antibody functions


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Tc

TargetTc


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TH cells play a central role in the immune system


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TH cells play a central role in the immune system


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CD4 + T cells in HIV infection


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Immunological tolerance

A state of unresponsiveness to a particular Ag - Ag specific

to Ags derived from bodys own tissues/cells- self tolerance to pathogen-derived/foreign Ags


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The concepts ofimmunological self & non-self

Immune system does not attack self tissues or cellsunder normal condition, but how?

Central tolerance thymic education

Peripheral tolerance failed-safe mechanisms


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Early in life (foetal stage)

T cells are important, which develop in the thymus

TCR specificities: randomly generated many auto-reactive

T cells recognize self components (Ag) in the thymus removed

Non-self reactive cells selected, matured & exported

Central tolerance thymic education


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Post- thymic continuing education not all self Ags present in the thymus

some auto-reactive cells can escape

Mechanisms: Deletion

Inactivation (anergy) Suppression

Peripheral tolerance


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Does the immune system mount responsessimply to anything that is non-self?

A question for thoughts:

Summary


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Immunity: Innate (natural) Adaptive (acquired)

Humoral (B cells, Abs) Cellular (T, NK, MQ)

The adaptive immunity: Key features: specificity & memory Types: humoral & cell-mediated responses Key players: T & B lymphocytes TH cells play a central role in the induction & maintenance of immune responses

Principle of vaccination: Vaccination protects us from infection by inducing protective immunity, through

establishment of specific immunological memory but bypassing the need forprimary infection

Immunological tolerance: Tolerance induction is Ag specific Central & peripheral mechanisms

Summary

The Adaptive Immune System - An Overview

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