Ch 6 Adaptive Immune

8/3/2019 Ch 6 Adaptive Immune

1/24

Chapter 6


2/24

The Adaptive ImmuneThe Adaptive ImmuneResponseResponse

In adaptive immunity, nonspecific

phagocytes present antigen to specific Tcells, triggering the production of effector

T cells and antibodies. Immune T cells

and antibodies react directly or indirectlyto neutralize or destroy the antigen.


3/24

The adaptive immune response is characterized byspecificityfor the antigen,

the ability to respond more vigorously when reexposed to thesame antigen (memory),

the ability to discriminate self antigens from nonself antigens(tolerance).


4/24


5/24


6/24


7/24

Acquired/Adaptive/Specific ImmunityFeatures

Specificity

Memory

Specialization

Self/Nonself recognition


8/24

Innate vs. adaptive immunityInnate vs. adaptive immunity Innate immunity

First line of defense (present in all individuals at alltimes)

Immediate (0 4 hours)

Non-specific

Does not generate lasting protective immunity

Adaptive (acquired) immune response(late: > 96 hours)

Is initiated if innate immune response is not adequate (>4 days)

Antigen-specific immunity

Generates lasting protective immunity (e.g. Antibodies,memory T-cells)

Humoral and cell-mediated


9/24

Immune system cellsImmune system cells

Innate immunityGranulocytes(i.e.neutrophils)

Macrophages

Dendritic cells

Natural killer (NK) cells

Adaptive immunity

LymphocyteB cells

T cells Cytotoxic T cells (CTLs)

Helper T cells (Th)

Memory cells

www.gcarlson.com/cellular_active_neutrophils.htmhttp://


10/24

Cells of the adaptive immune

systemDendritic cells (most importantAPC cell)

B-cells

Humoral immune responseProduce antibodies

APC cells

T- cells

Cell-mediated immune responseCytotoxic T cells (CD8)

Helper T cells (CD4)

Memory cellshttp://www.biology.arizona.edu/immunology/tutorials/immunology/graphics/T_helper_act.gif


11/24

Induction of the adaptiveInduction of the adaptive

immune responseimmune response

Pathogen ingested byPathogen ingested by

immature dendritic cellimmature dendritic cell

Migrate to the lymphMigrate to the lymph

nodesnodes

Interact with nave TInteract with nave T

lymphocyteslymphocytes

Activates

TH1

MHC II

Macrophage

Dead intracellular bacteria


12/24

Lymphocytes (effector cells ofLymphocytes (effector cells of

the adaptive immune system)the adaptive immune system)

Lymphocytes (effector cells ofLymphocytes (effector cells of

the adaptive immune system)the adaptive immune system) Antigen receptors with single specificity (T and B cells)

GeneGene rere--arrangementarrangement

Clonal selection

InteractionInteraction ofof antigenantigen andand lymphocytelymphocyte receptorreceptor ActivationActivation ofof lymphocytelymphocyte

DifferentiationDifferentiation (progeny(progeny withwith identicalidentical specificity)specificity)

T and B cells have 2 distinct recognition systems for detectingpathogens

TT cellscells -- recognizerecognize intracellularintracellular pathogenspathogens (T(T cellcell receptors,receptors,TCR)TCR)

BB cellscells recognizerecognize extracellularextracellular pathogenspathogens(Immunoglobins,(Immunoglobins, BCRBCR

Antigen receptors with single specificity (T and B cells)

GeneGene rere--arrangementarrangement

Clonal selection

InteractionInteraction ofof antigenantigen andand lymphocytelymphocyte receptorreceptor ActivationActivation ofof lymphocytelymphocyte

DifferentiationDifferentiation (progeny(progeny withwith identicalidentical specificity)specificity)

T and B cells have 2 distinct recognition systems for detectingpathogens

TT cellscells -- recognizerecognize intracellularintracellular pathogenspathogens (T(T cellcell receptors,receptors,TCR)TCR)

BB cellscells recognizerecognize extracellularextracellular pathogenspathogens(Immunoglobins,(Immunoglobins, BCRBCR


13/24

A single progenitor cellgives rise to a large

number of lymphocytes,each with a different

specificity

Clonal selection

Pool of navelymphocytes

Selfantigen

Selfantigen

Removal of potentially

self-reactive immaturelymphocytes by clonal

deletion

Foreign antigenProliferation anddifferentiation ofactivated specific

lymphocytes to forma clone of effector

cellsEffector cellseliminate antigen


14/24

Membrane-bound form of the

antibody

V-region (variable) Antigen-binding specificity

Fc-region (constant)

Determines how the

antibody disposes of thebound pathogen

Fc region

V region; At binding


15/24

Single antigenrecognition site

Always a cell surfacemolecule


16/24

Effector cellsActive-duty cells

Die off during or just

afterbattle

Memory cellsReserve cellsCalled up to the

front for later battles

Antigen

T cellor

B cell

Active duty?

Reserves?

cloneclonefamily of cellsfamily of cells

descended from onedescended from one

ancestor cellancestor cell

cloneclonefamily of cellsfamily of cells

descended from onedescended from one

ancestor cellancestor cellNaveActiveChemicalsignal


17/24


18/24

Humoral immune responseHumoral immune response

Cell-surface immunoglobulin receptors

(BCR) detect extracellular pathogens

Once activated, secrete immunoglobulins as

soluble antibodies

Antibodies

Variable region (2 identical antigen-binding

sites) Constant region (determines how antibody

disposes of the pathogen once it is bound)

Cell-surface immunoglobulin receptors

(BCR) detect extracellular pathogens

Once activated, secrete immunoglobulins as

soluble antibodies

Antibodies

Variable region (2 identical antigen-binding

sites) Constant region (determines how antibody

disposes of the pathogen once it is bound)


19/24


20/24

Generation of Antibody Diversity: Production

of Unique Fab Sites through Gene

Translocation

the immune system of the body has no idea as to whatantigens it may eventually encounter.

Therefore, it has evolved a system that possesses thecapability of responding to any conceivable antigen.

The immune system can do this because both B-

lymphocytes and T-lymphocytes have evolved aunique system of gene-splicing called genetranslocation , a type ofgene-shuffling process wherevarious different genes along a chromosome are cutout of one location and joined with other genes

along the chromosome.


21/24

Clonal Selection and Clonal

Expansion

Clonal Selection and Clonal

Expansion

During its development, each B-lymphocytebecomes genetically programmed, through aprocess called gene translocation, to make aunique antibody molecule that will functionas a B-cell receptor.

Molecules of that antibody are then placedon the cell's surface where it can react withepitopes of an antigen.

Cytokines from an activated T4-lymphocytenow enable the activated B-lymphocyte toproliferate into a large clone of identical B-lymphocytes.

The B-lymphocytes now differentiate intoantibody-secreting B-lymphocytes andplasma cells that secrete large quantities ofantibodies "fitting" the original epitope.Some B-lymphocytes differentiate into B-memory cells capable of anamnesticresponse .


22/24

Antibody interactions

Antibodies can participate in host defenses in 3 mainways:

Neutralization

Ab bind and neutralize bacterial toxins, bacteria andvirus particles preventing interaction with host cells

Ingestion by macrophages

Opsonization Allows recognition by phagocytes or NK cells (antibody-

dependent cell mediated cytotoxicity, ADCC)

Ingestion or killing

Complement activation Activation of complement system

Ingestion by phagocytes


23/24

Antigen recognition by T-cells

T cells detect presence of intracellular

pathogens

T cells receptors

Peptide fragments

Major histocompatibility complex (MHC)

MHC I (cytotoxic T cells /CD+8)

MHC II (T helper (1 and 2)/ CD+4)

Cell death


24/24

Antigen recognition by T-cells

Cytotoxic T cells (CD8)recognize antigen

presented by MHC I

and kills thecell

Kills

CytotoxicT cell

MHC I

TH1 cells (CD4)recognize antigen

presented by MHC II

and activatesmacrophages

TH2 cells (CD4)recognize antigen

presented by MHC II

and activates B cells

Activates

TH1

MHCII

Macrophage

Virus-infected cell

Apoptoticcell

Dead intracellularbacteria

Activates

TH2

MHCII

B cell

Anti-toxin antibodies

Ch 6 Adaptive Immune

Documents