aspectos basicos inmun peru 2013

8/22/2019 Aspectos Basicos Inmun Peru 2013

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ASPECTOS BASICOS DELSISTEMA INMUNE

Dr Heraldo Povea PacciMD (Chile) MSc (Gran Bretaa) Fellow (EEUU) PhD (Australia)

Miembro Comit Inmunizaciones Ministerio Salud Chile

Profesor Asociado . Universidad Diego Portales Chile

Especialista en Inmunologia y Salud Sexual

Consultor en Educacion Superior


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Plan de la presentacion

Nomenclatura

Componentes del sistema de defensas Las respuestas defensivas

Control del sistema

Alteraciones del sistema


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Definitions

Immune system = cells, tissues, and moleculesthat mediate resistance to infections

Immunology = study of structure and function of

the immune system

Immunity = resistance of a host to pathogens and

their toxic effects

Immune response = collective and coordinated

response to the introduction of foreignsubstances in an individual mediated by the cells

and molecules of the immune system


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Role of the immunesystem Defense against microbes

Defense against the growth of tumor cells

kills the growth of tumor cells

Homeostasis

destruction of abnormal or dead cells

(e.g. dead red or white blood cells, antigen-

antibody complex)

Other unknown functions?


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ORGANOS CENTRALES

Mdula sea

Timo

ORGANOS PERIFRICOS

Adenoides

Amgdalas

Ganglios linfticos

Bazo

Apndice

Placas de Peyer

BALT (Tejido linftico asociado abronquios)

GALT (Tejido linftico asociado a intestino)

SALT (Tejido linftico asociado a la piel)

ORGANOS DEL SISTEMA INMUNE


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Clula tronco pluripotencial de la mdula sea

Progenitor linfoideProgenitor B Clula NK Progenitor T

Clula pre-B Pre-Timocito

Clula B inmadura Timocito inmaduro

Clula B madura Timocito maduroLinfocito B Linfocito T

Clula Plasmtica Linfocitos Th y Tc

Inmunoglobulinas Linfoquinas

IgM Th1 Th2

IgG IL-2 IL-3 IL-4

IgA INF-g GM-CSF IL-13

IgE TGF-b IL-5

IgD IL-9

FUNCIONES

Respuestainmune humoral

Memoria

Respuestainmune celular

Hipersensibilidad

retardada

Citotoxicidad

Memoria

prolongadaInmunidad

anti-tumoral y

anti-viral

Citotoxicidad NK

CLULAS DEL SISTEMA INMUNE


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LINFOCITOS T

Representan el 60-70% de los linfocitosperifricos.

Ubicados en regiones paracorticalesde ganglios linfticos y manguitosperiarteriolares del bazo.

Genticamente programados parareconocer un antgeno especfico pormedio de su receptor especfico (TCR).


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LINFOCITOS T

Marcadores comunes:

CD2, CD7, CD3, CD28

CD4+: linfocitos T cooperadores/inductores

CD8+: linfocitos T citotxicos/supresores

CD4 y CD8 son mutuamente excluyentes

Relacin CD4 : CD8 = 2 : 1


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LINFOCITOS TMolculas de Superficie de las Th y Tc

Linfocito T

ICAM-1 y LFA-1 sonmolculas deadhesin celular


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Chapter 21, Immune System 10

T Cell Selection in the Thymus

Figure 21.7


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LINFOCITOS TComplejo Receptor de las Clulas T (TCR)

Sitio de unin del antgeno

CD3cadenas gamma,

delta y epsilon

TCR

alfa - beta

CD3

cadenas theta


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LINFOCITOS B

Representan el 10- 20% de linfocitos circulantes

Ubicados en centros germinales y folculos

linfoides de ganglios, bazo, amgdalas y tejidolinfoide asociado a mucosas

Se transforman en clulas plasmticas para lasecrecin de inmunoglobulinas

Reconocen especficamente a los antgenosmediante su complejo receptor especfico BCRcompuesto por cadenas y cadenas Ig

Marcadores especficos: CD19, CD21.


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LINFOCITOS B

CLULA PLASMTICA

Marcadores desuperficie


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Display a unique type of receptor that responds to a distinctantigen

Become immunocompetent before they encounter antigensthey may later attack

Are exported to secondary lymphoid tissue whereencounters with antigens occur

Mature into fully functional antigen-activated cells uponbinding with their recognized antigen

It is genes, not antigens, that determine which foreignsubstances our immune system will recognize and resist

Immunocompetent B or T cells


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Red

bone marrow

1

2

3

Immunocompetent ,

but st i l l naive,

lymphocyte

migrates via blood

Mature (antigen-activated)immunocompetent lymphocytescirculate continuously in thebloodstream and lymph andthroughout the lymphoid organs ofthe body.

Key: = Site of lymphocyte origin

= Site of development of immunocompetenceas B or T cells; primary lymphoid organs

= Site of antigen challenge and finaldifferentiation to activated B and T cellsImmature

lymphocytesCirculation inblood

1

1 Lymphocytes destined to become Tcells migrate to the thymus and developimmunocompetence there. B cellsdevelop immunocompetence in redbone marrow.

Thymus

Bone

marrow

Lymph nodes ,

spleen, and other

lympho id t issues

2 2 After leaving the thymus or bonemarrow as naive immunocompetentcells, lymphocytes seed the lymph

nodes, spleen, and other lymphoidtissues where the antigen challengeoccurs.

3 3

ActivatedimmunocompetentB and T cellsrecirculate in bloodand lymph

Immunocompetent B or T cells

Figure 21.8


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CLULAS CITOLITICAS NATURALES(NK)

Representan el 5 a 10% de linfocitos perifricos

Marcadores: CD2, CD56 y CD16 (receptor para

Fc de IgG) No presentan receptores especficos para los

antgenos ni inmunoglobulinas de superficie

Capacidad de lisar de clulas neoplsicas,clulas infectadas por virus y algunas clulasnormales por citotoxicidad directa odependiente de anticuerpos que se fijan a sus

receptores para Fc de IgG (ADCC)


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Marcadores de superficie

CLULAS CITOLITICAS NATURALES(NK)

Reconocen las clulas propias a

travs de un receptor que se une a

molculas clase I (C) del MHC para

inhibir sus accin citoltica


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GRANULOCITOSFagocitos PMN

Primera respuesta inflamatoria

Secretan enzimas proteolticas (mieoloperoxidasa)

Migran de la sangre a los tejidos por factoresquimiotcticosSobrevida y proliferacin inducida por IL-5

Respuestas alrgicas y contra los parsitos(citotoxicidad)

Clulas circulante que, junto con los MASTOCITOStisulares, secretan mediadores qumicos (Histamina)en las reacciones alrgicas tipo I mediadas por elentrecruzamiento de molculas IgE adheridas a losreceptores de memebrana


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CLULAS PRESENTADORAS DEANTGENOS (CPA)

Se originan a partir de progenitores comunes degranulocitos-monocitos por accin de la IL-3, GM-CSF y M-CSF

Circulan por la sangre, migran a los tejidos y sediferencian en macrfagos

Fagocitos tisulares

Segregan citoquinas, enzimas proteolticas yfactores citotxicos

Presentadoras de antgenos profesionales

Se encuentran en superficies tisulares mucosos ycutneas. Captan los antgenos y migran a losganglios linfticos


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CLULAS PRESENTADORAS DE ANTGENOSMACRFAGOS

Sistema monocito-macrofgico

Procesan y presentan el antgeno a clulas T

Producen (IL-1 e IFN-alfa)

Secretan metabolitos

txicos y enzimas

Son clulas efectoras

en algunas formas deinmunidad celular,

tal como en las reacciones

de hipersensibilidad retardada.


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CLULAS PRESENTADORAS DE ANTGENOSCLULAS DENDRTICAS y de LANGERHENAS

Presentan prolongaciones citoplasmticas

dendrticas y gran cantidad de molculas

MHC tipo II

Son excelentes

presentadores de

antgenos

Poca o ninguna capacidad fagoctica.


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CITOQUINAS

Molculas que inducen y regulan la respuestainmunitaria mediante el establecimiento deinteracciones con receptores especficos

presentes en linfocitos, monocitos, clulasinflamatorias y clulas endoteliales.

Son producidas por distintos tipos de clulas.

Efecto pleiotrpico (actan sobre muchos tiposcelulares) con accin autocrina, paracrina yendocrina.


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Epithelial Chemical Barriers

Epithelial membranes produce protective

chemicals that destroy microorganisms

Skin acidity (pH of 3 to 5) inhibits bacterial

growth

Sebum contains chemicals toxic to bacteria

Stomach mucosae secrete concentrated HCl

and protein-digesting enzymes Saliva and lacrimal fluid contain lysozyme

Mucus traps microorganisms that enter the

digestive and respiratory systems


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Surface Barriers (First Line of

Defense) Skin, mucous membranes, and their

secretions make up the first line of

defense

Keratin in the skin:

Presents a formidable physical barrier to most

microorganisms

Is resistant to weak acids and bases, bacterialenzymes, and toxins

Mucosae provide similar mechanical

barriers


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Innate immunity

Based on genetic make-up

Relies on already formed components

Rapid response: within minutes of infection

Not specific

same molecules / cells respond to a range of

pathogens

Has no memory

same response after repeated exposure

Does not lead to clonal expansion


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Innate immunity: mechanisms Mechanical barriers / surface secretion

skin, acidic pH in stomach, cilia

Humoral mechanisms

lysozymes, basic proteins, complement, interferons

Cellular defense mechanisms natural killer cells neutrophils, macrophages,, mast cells,

basophils, eosinophils

Neutrophil NK Cell MonocyteMacrophage

Basophils &Mast cells

Eosinophils


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Mechanism of Phagocytosis

Microbes adhere to the phagocyte

Pseudopods engulf the particle (antigen)

into a phagosome

Phagosomes fuse with a lysosome to form

a phagolysosome

Invaders in the phagolysosome are

digested by proteolytic enzymes

Indigestible and residual material is

removed by exocytosis


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Mechanism of Phagocytosis

Figure 21.1a, b


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3. Inflammation: Tissue

Response to Injury The inflammatory response is triggered

whenever body tissues are injured

Prevents the spread of damaging agents to

nearby tissues

Disposes of cell debris and pathogens

Sets the stage for repair processes

The four cardinal signs of acuteinflammation are redness, heat, swelling,

and pain


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Neutrophilsenter bloodfrom bonemarrow

1

2

3

4

Margination

Diapedesis

Positivechemotaxis

Capillary wallEndothelium

Basal lamina

Inflammatorychemicalsdiffusing fromthe inflamedsite act aschemotacticagents

Inflammatory Response: Phagocytic Mobilization

Figure 21.3


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4. Antimicrobial Proteins

Enhance the innate defenses by:

Attacking microorganisms directly

Hindering microorganisms ability to

reproduce

The most important antimicrobial proteins

are:

Interferon

Complement proteins


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Interferon Family

Interferons are a family of related proteins each with slightlydifferent physiological effects

Lymphocytes secrete gamma () interferon, but most other

WBCs secrete alpha () interferon

Fibroblasts secrete beta () interferon

Interferons also activate macrophages and mobilize NKs

FDA-approved alpha IFN is used:

As an antiviral drug against hepatitis C virus

To treat genital warts caused by the herpes virus


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20 or so proteins that circulate in the blood

in an inactive form

Proteins include C1 through C9, factors B,

D, and P, and regulatory proteins

Provides a major mechanism for

destroying foreign substances in the body

4 b. Complement

C l t P th


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Complement Pathways

Figure 21.5


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Toll-like Receptors (TLRs)

Macrophages and cells lining the

gastrointestinal and respiratory tracts bear

TLRs

TLRs recognize specific classes of

infecting microbes

Activated TLRs trigger the release of

cytokines that promote inflammation


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Immunity: Two Intrinsic Defense

Systems Innate (nonspecific) system responds

quickly and consists of:

First line of defense intact skin and mucosae prevent entry of

microorganisms

Second line of defense antimicrobial proteins, phagocytes, and

other cells Inhibit spread of invaders throughout the body

Inflammation is its hallmark and most important mechanism


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Internal Defenses (Second Line

of Defense) The body uses nonspecific cellular and chemical

devices to protect itself

1. Phagocytes

2. natural killer (NK) cells

3. Inflammatory response enlists macrophages, mast

cells, WBCs, and chemicals

4. Antimicrobial proteins in blood and tissue fluid

Harmful substances are identified by surface

carbohydrates unique to infectious organisms


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Adaptive immunity:

second line of response Based upon resistance acquired during life

Relies on genetic events and cellular growth

Responds more slowly, over few days

Is specific

each cell responds to a single epitope on an antigen

Has anamnestic memory

repeated exposure leads to faster, stronger response

Leads to clonal expansion


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Adaptive Immunity: Anatomy of the response

Nave T cells and B cells recirculate between lymph

nodes, spleen, and the blood.

Antigen is taken from site of infection to the lymph node

either by the flow of lymph or is carried by a maturing

dendritic cell that migrates along the lymphatics.

The dendritic cell presents antigen to nave T cells in the

lymph node to initiate the T cell immune response.

Activated T cells, after they have expanded in number,

leave the lymph node and go via the blood to sites of

inflammation, where they look for their antigen to

mediate cell-mediated immunity.

I i T I i i D f


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Immunity: Two Intrinsic Defense

Systems

Adaptive (specific) defense system

Third line of defense mounts attack against

particular foreign substances

Takes longer to react than the innate system

Works in conjunction with the innate system

Ad ti (S ifi ) D f (Thi d Li


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The adaptive immune system is a

functional system that:

Recognizes specific foreign substances

Acts to immobilize, neutralize, or destroy

foreign substances

Amplifies inflammatory response and

activates complement

Adaptive (Specific) Defenses (Third Line

of Defense)

Adaptive Immune Defenses


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The adaptive immune system is antigen-

specific, systemic, and has memory

It has two separate but overlapping arms

Humoral, or antibody-mediated (B Cell)

immunity

Cellular, or cell-mediated (T Cell) immunity

Adaptive Immune Defenses

Adaptive Immunity:


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Adaptive Immunity:

active and passive

Active Immunity Passive Immunity

Natural clinical, sub-clinical

infection

via breast milk,

placenta

Artificial Vaccination:

Live, killed, purified

antigen vaccine

immune serum,

immune cells


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Adaptive immunity: mechanisms

Cell-mediated immune response (CMIR)

T-lymphocytes

eliminate intracellular microbes that survive

within phagocytes or other infected cells

Humoral immune response (HIR)

B-lymphocytes

mediated by antibodies eliminate extra-cellular

microbes and their toxins Plasma cell(Derived from B-lymphocyte,produces antibodies)


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Adaptive Immunity: Antibodies I

We can make millions or billions of different

antibodies, each highly specific for a singlemolecule (ideally a pathogen molecule)

As it develops, each B lymphocyte alters its DNA

so it makes ONE antibody; each B lymphocyte isan individual, its antibody is unique

A molecule that induces the production of an

antibody is called an antigen

In a normal immune response, several B cellsthat make antibodies that recognize the infectious

agent become activated, each multiply to form a

clone. These progeny then become antibody-secretin factories.


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Adaptive Immunity: Antibodies II

Often, B cells are helped by T lymphocytes which alsorecognize the pathogen, these B cells take longer to makeantibodies, but make higher quality antibodies (bind morestrongly). Some of these high quality-producing B cellsturn into antibody-secreting factories that go to the bone

marrow and last a very long time (years). The antibodythey produce can protect us immediately when thatinfectious agent returns and prevent noticeable illness

This type of high quality/long lasting immune response(germinal center response) is the mechanism behindalmost all successful vaccines; understanding thisprinciple was used to greatly improve a class of vaccinesagainst bacterial pathogens, resulting in the conjugate

vaccines (starting in the 1990s)


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Adaptive Immunity: Cell-mediated immunity I

T lymphocytes recognize small pieces of proteins (peptides)

associated with our own cells. They do this with the T cell antigen receptor orTCR which is like

an antibody, but always on the surface of the T cell, neversecreted.

Therefore the T cell only functions locally next to cells that that

have its antigen. As with B cells, T cells alter their DNA such that each T cell makesa unique TCR and different T cells recognize different antigens

There are two types of T cells: helper T cells and killer (orcytotoxic) T cells

Helper T cells express a molecule called CD4 and are the cells thatare infected by HIV-1; their depletion leads to theimmunodeficiency of AIDS

Cytotoxic T cells express a similar molecule called CD8

Antigens


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Substances that can mobilize the immune

system and provoke an immune response

The ultimate targets of all immune

responses are mostly large, complex

molecules not normally found in the body

(nonself)

Antigens

Complete Antigens


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Important functional properties:

Immunogenicity the ability to stimulate

proliferation of specific lymphocytes and

antibody production Reactivity the ability to react with the

products of the activated lymphocytes and the

antibodies released in response to them

Complete antigens include foreign protein,

nucleic acid, some lipids, and large

polysaccharides

Complete Antigens

Haptens (Incomplete Antigens)


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Small molecules, such as peptides,

nucleotides, and many hormones,

not immunogenic (does not stimulate a response)

reactive when attached to protein carrier.

If they link up with the bodys proteins, the

adaptive immune system may recognizethem as foreign and mount a harmful

attack (allergy)

Haptens (Incomplete Antigens)

Antigenic Determinants


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Only certain parts of an entire antigen are immunogenic

Antibodies and activated lymphocytes bind to theseantigenic determinants

Most naturally occurring antigens have numerousantigenic determinants that:

Mobilize several different lymphocyte populations

Form different kinds of antibodies against it

Large, chemically simple molecules (e.g., plastics) havelittle or no immunogenicity




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Figure 21.6

Self-Antigens: MHC Proteins


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Our cells are dotted with protein molecules (self-

antigens) that are not antigenic to us but are strongly

antigenic to others (reason for transplant rejection)

One type of these, MHC proteins, mark a cell as self

The two classes of MHC proteins are:

Class I MHC proteins found on virtually all bodycells

Class II MHC proteins found on certain cells in the

immune response

Self-Antigens: MHC Proteins

MOLCULAS DE


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MOLCULAS DEHISTOCOMPATIBILIDAD

Molculas glucoproteicas de la superficie de lasclulas que se unen a fragmentos peptdicos, afin de presentarlos a las clulas T especficas

Son importantes en el rechazo de transplantes yen la predisposicin a enfermedades

Varios genes codifican antgenos de

histocompatibilidad, pero los principales seubican en el brazo corto del cromosoma 6 en elComplejo mayor de histocompatibilidad (MHC)

CATEGORIAS DEL COMPLEJO MAYOR


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CATEGORIAS DEL COMPLEJO MAYORDE HISTOCOMPATIBILIDAD (MHC)

Genes clase I (HLA-A, HLA-B y HLA-C) yII (HLA-DR, HLA-DQ y HLA-DP) codificanglucoprotenas de superficie celular.

Genes clase III codifican componentesdel sistema del complemento.

CLASE II CLASE III CLASE ICITO-QUINAS

B C ATNFComplemento

DP DQ DR


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CITOQUINAS

Molculas que inducen y regulan la respuestainmunitaria mediante el establecimiento deinteracciones con receptores especficos

presentes en linfocitos, monocitos, clulasinflamatorias y clulas endoteliales.

Son producidas por distintos tipos de clulas.

Efecto pleiotrpico (actan sobre muchos tiposcelulares) con accin autocrina, paracrina yendocrina.

CITOQUINAS


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Citoquinas pro-inflamatorias que median lainmunidad natural:

(IL-1, TNF-alfa, IFN-gamma, IL-8).

Citoquinas que regulan el crecimiento,activacin y diferenciacin de los linfocitos(IL-2, IL-4, IL-10, IL-12 y TGF-beta).

Ciroquinas que estimulan a otras clulas(IL-13 a linfocitos B, IL-5 a eosinfilos)

Citoquinas que estimulan la hematopoyesis

(GM-CSF, M-CSF, IL-3).

CITOQUINASClasificacin

Humoral Immunity Response


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Antigen challenge first encounter

between an antigen and a naive

immunocompetent cell

Takes place in the spleen or otherlymphoid organ

If the lymphocyte is a B cell:

The challenging antigen provokes a humoral

immune response

Antibodies are produced against the challenger

Humoral Immunity Response

Clonal Selection


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Clonal Selection

Figure 21.9

Fate of the Clones


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Most clone cells become antibody-

secreting plasma cells

Plasma cells secrete specific antibody at

the rate of 2000 molecules per second

Fate of the Clones

Fate of the Clones


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Secreted antibodies:

Bind to free antigens

Mark the antigens for destruction by specific

or nonspecific mechanisms

Clones that do not become plasma cells

become memory cells that can mount an

immediate response to subsequentexposures of the same antigen

Fate of the Clones

Immunological Memory


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Primary immune response cellular

differentiation and proliferation, which

occurs on the first exposure to a specific

antigen Lag period: 3 to 6 days after antigen

challenge

Peak levels of plasma antibody are achievedin 10 days

Antibody levels then decline




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Secondary immune response re-

exposure to the same antigen

Sensitized memory cells respond within hours

Antibody levels peak in 2 to 3 days at muchhigher levels than in the primary response

Antibodies bind with greater affinity, and their

levels in the blood can remain high for weeksto months


Summary of the Primary Immune Response


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Summary of the Primary Immune Response

Figure 21.19

P i d S d H l R


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Primary and Secondary Humoral Responses

Figure 21.10

Active Humoral Immunity


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B cells encounter antigens and produce

antibodies against them

Naturally acquired response to a bacterial or

viral infectionArtificially acquired response to a vaccine of

dead or attenuated pathogens

Vaccines spare us the symptoms of disease, and

their weakened antigens provide antigenic

determinants that are immunogenic and reactive

Active Humoral Immunity

Passive Humoral Immunity


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Differs from active immunity in the antibody source andthe degree of protection

B cells are not challenged by antigens

Immunological memory does not occur

Protection ends when antigens naturally degrade inthe body

Naturally acquired from the mother to her fetus via theplacenta

Artificially acquired from the injection of serum, such asgamma globulin

Passive Humoral Immunity

Types of Acquired Immunity


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Types of Acquired Immunity

Figure 21.11

RESPUESTA INMUNE


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RESPUESTA INMUNERECONOCIMIENTO DE ANTGENOS

Presentacin delpptido antignicoen la fosa o canalde la molculaMHC clase I a un

linfocito T CD8+ ocitotxico

CLULA PRESENTADORA DE ANTGENOSMolcula Clase II del MHC


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RESPUESTAINMUNEPRESENTACINDEL ANTGENO

Molcula Clase II del MHC

CLULA T CD4*

Presentacin del pptidoantignico por molculasMHC clase II a las clulas

T CD4+ (helper).Importancia de lasmolculas co-estimulatoriasCD28 y B7

RESPUESTA INMUNE


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RESPUESTA INMUNEINDUCCIN

Alergeno

Th 0

Th 1

Th 2


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Sntesis de las Inmunoglobulinas

El tipo de anticuerpo resultante depende del perfil de citoquinas

secretado por las clulas Th en respuesta a la presentacin del Ag

Antibodies


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Also called immunoglobulins

Constitute the gamma globulin portion of blood

proteins

Are soluble proteins secreted by activated B cells and

plasma cells in response to an antigen

Are capable of binding specifically with that antigen

There are five classes of antibodies: IgD, IgM, IgG, IgA,

and IgE

I l b li


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Inmunoglobulinas

Cada monmero se forma por la

unin no covalente de dos cadenaslivianas (kappa o lambda) y dos

cadenas pesadas especficas de

cada isotipo de inmunoglobulina:

IgM cadenas

IgG cadenas

IgA cadenas

IgE cadenas

IgD cadenas

Sus funciones biolgicas dependen

del fragmento Fc:

Fijacin de complemento (IgM eIgG)

Unin a receptores celulares (IgG,

IgM, IgE)

Pasaje placentario (IgG)

Pasaje a mucosas (IgA)

Antibody Targets


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Antibodies themselves do not destroy

antigen; they inactivate and tag it for

destruction

All antibodies form an antigen-antibody(immune) complex

Defensive mechanisms used by antibodies

are neutralization, agglutination,precipitation, and complement fixation

y g

Mechanisms of Antibody Action


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y

Figure 21.13

Funcin de las Inmunoglobulinas


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IgAPredominante en secreciones seromucosas(saliva, secreciones traqueo-bronquiales,vaginales, etc.)Se presenta como dmero (impide protelisis

por enzimas digestivas).IgG Principal anticuerpo de respuesta secundaria

(memoria).

Actividad anti-virus, bacterias, parsitos yalgunos hongosCruzan placenta (inmunidad pasiva trans-placentaria, 3-6 meses post-parto)

Activa complemento por va clsica.




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IgM Principal anticuerpo de respuesta inmuneinmediata y primariaSe presenta como pentmero en asociacincon cadena "J

Activa complemento por va csicaIgE Se une a receptores de alta afinidad en

basofilos y mastocitos

Participa en respuestas anti-helmintos ehipersensibilidad inmediata (anafilaxia)

IgD Se encuentra circulante y en la superficie delas clulas B maduras


Cell-Mediated Immune Response


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Since antibodies are useless against intracellularantigens, cell-mediated immunity is needed

Two major populations of T cells mediate cellularimmunity

CD4 cells (T4 cells) are primarily helper T cells (TH) CD8 cells (T8 cells) are cytotoxic T cells (TC) that

destroy cells harboring foreign antigens

Other types of T cells are:

Suppressor T cells (TS) Memory T cells

p

Major Types of T Cells


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j yp

Figure 21.14

Importance of Humoral Response


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Soluble antibodies

The simplest ammunition of the immune

response

Interact in extracellular environments such asbody secretions, tissue fluid, blood, and lymph

p p

Importance of Cellular Response


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T cells recognize and respond only toprocessed fragments of antigen displayed

on the surface of body cells

T cells are best suited for cell-to-cellinteractions, and target:

Cells infected with viruses, bacteria, or

intracellular parasitesAbnormal or cancerous cells

Cells of infused or transplanted foreign tissue

p p

Class I MHC Proteins


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Chapter 21, Immune System 83Figure 21.15a

Class II MHC Proteins


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Figure 21.15b

T Cell Activation: Step One Antigen Binding


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Chapter 21, Immune System 85Figure 21.16

Helper T Cells (TH)


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H

Figure 21.17a

Helper T Cells


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Chapter 21, Immune System 87Figure 21.17b

Cytotoxic T Cell (Tc)


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TC cells, or killer T cells, are the only T cells that candirectly attack and kill other cells

They circulate throughout the body in search ofbody cells that display the antigen to which they

have been sensitized Their targets include:

Virus-infected cells

Cells with intracellular bacteria or parasites

Cancer cells Foreign cells from blood transfusions or transplants

Mechanisms of Tc Action


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aspectos basicos inmun peru 2013

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