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ADAPTIVE IMMUNITY

• IMMUNITY CAN BE ACQUIRED IN TWO WAYS

1. ACTIVE IMMUNITY RESULTS FROM ACTIVATION OF AN

INDIVIDUAL’S OWN LYMPHOCYTES

• PATHOGEN INFECTION OR VACCINATION

2. PASSIVE IMMUNITY RESULTS FROM OBTAINING ANOTHER

INDIVIDUAL’S ANTIBODIES

• TRANSFER OF MATERNAL ANTIBODIES ACROSS PLACENTA

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ADAPTIVE IMMUNITY

• ORGANS OF THE IMMUNE SYSTEM

• PRIMARY LYMPHOID ORGANS

• BONE MARROW AND THYMUS

• SECONDARY LYMPHOID ORGANS

• LYMPH NODES, SPLEEN, AND MUCOSAL-ASSOCIATED

LYMPHOID TISSUE (MALT)

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• Organs of the immune system

• Primary lymphoid organs

• Bone marrow

• Thymus

• Secondary lymphoid organs

• Lymph nodes

• Spleen

• Mucosa-associated

lymphoid tissue or MALT

Thymus

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Spleen

Tonsils

Cervical lymph nodes

Axillary

lymph nodes

Mucosa-

associated

lymphatic

tissue

(MALT) (in

small intestine)

Inguinal

lymph

nodes

Lymphatic vessels

Red bone marrow

CELL-MEDIATED IMMUNITY

• T LYMPHOCYTES ARE OF TWO TYPES

• CYTOTOXIC T CELLS (TC)

• CD8+ CELLS

• HELPER T CELLS (TH)

• CD4+ CELLS

• DISTINGUISHED BY TYPE OF MHC MARKERS RECOGNIZED AND

ROLES AFTER ACTIVATION

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CELL-MEDIATED IMMUNITY

• CYTOTOXIC T CELLS

• RECOGNIZE “ALTERED-SELF”CELLS, PARTICULARLY THOSE THAT ARE

VIRALLY INFECTED OR TUMOR CELLS

• RECOGNIZE FOREIGN PEPTIDES BOUND TO SELF-MHC CLASS I PROTEINS

• CLONAL EXPANSION AND DIFFERENTIATION INTO ACTIVATED CELLS AND

MEMORY CELLS

• ACTIVATED CELLS INDUCE APOPTOSIS IN CELLS WITH SAME SPECIFICITY

AS FIRST CELL

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Cytotoxic T cells induce apoptosis

of “altered-self” cells. And destroy

tumors

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Dendritic cell

CD8CytokinesCytokines

Virus

MHC class I

Viral peptide

TCR specific for this

MHC–peptide complex

Naive cytotoxic T cell

Memory cytotoxic T cells Activated cytotoxic T cells

Clonal

expansion

Destroys

altered cell

Persists after

alter ed cells

are destroyed

Infected cell

Apoptosis of infected cell

a. 2500× b. 2500×

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a-b: © Dr.Andrejs Liepins/Photo Researchers, Inc.

CELL-MEDIATED IMMUNITY

• HELPER T CELLS

• SECRETE CYTOKINES THAT PROMOTE ACTIVATION OR DIFFERENTIATION

OF IMMUNE SYSTEM CELLS

• TH CELLS RESPOND TO EXOGENOUS ANTIGEN THAT IS TAKEN UP BY AN

ANTIGEN PRESENTING CELL

• ANTIGEN IS PARTIALLY DIGESTED, THEN COMPLEXED WITH MHC CLASS II

PROTEINS

• COMPLEX IS TRANSPORTED TO AND DISPLAYED ON THE CELL SURFACE

• ACTIVATED TH CELLS GIVE RISE TO EFFECTOR CELLS AND MEMORY CELLS

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Dendritic cell

CD4

B7

CD28

Bacterial peptide

Cytokines (IL-2)

Cytokines (IL-4)

Antigen

(such as a

bacterium) MHC class II

TCR specific for this MHC–peptide complex

Clonal

expansion

Memory helper T cell

Activated

helper T cell

Memory B cell

Naive B cell

Clonal

expansion

Plasma cells secreting antibody specific to this antigen

Humoral Response Cellular Response

Macrophage that can

better destroy invading

antigens

Cytokines (IFN-)

Activated

helper T cell

Memory helper T cell

Naive

helper T cell

Cytokines (IL-12)

Macrophage

HUMORAL IMMUNITY• BEGINS WHEN NAIVE B CELLS IN SECONDARY LYMPH ORGANS

MEET ANTIGENS

• B CELLS ARE ACTIVATED WHEN THEIR SURFACE IGS BIND TO A

SPECIFIC EPITOPE ON AN ANTIGEN

• TH CYTOKINES MAY ALSO BE REQUIRED

• ACTIVATION RESULTS IN CLONAL EXPANSION AND

DIFFERENTIATION INTO PLASMA AND MEMORY CELLS

• PLASMA CELLS PRODUCE SOLUBLE ANTIBODIES AGAINST THE

SAME EPITOPE

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IMMUNE RESPONSES

• THE FIRST ENCOUNTER WITH A FOREIGN ANTIGEN IS CALLED THE

PRIMARY IMMUNE RESPONSE

• ONLY FEW B OR T CELLS CAN RECOGNIZE ANTIGEN AND MOUNT RESPONSE

• CLONAL EXPANSION OCCURS – MEMORY CELLS

• SECOND ENCOUNTER IS CALLED THE SECONDARY IMMUNE RESPONSE

• THIS TIME THERE IS A LARGE CLONE OF MEMORY CELLS THAT CAN

RECOGNIZE THE ANTIGEN

• IMMUNE RESPONSE IS FASTER AND MORE EFFECTIVE

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11Development of active immunity to smallpox

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Am

ou

nt

of

an

tib

od

y

Exposure

to cowpoxTime

Exposure

to cowpox

Primary response

Secondary response

This interval

may be years

IgM

IgG

AUTOIMMUNITY

• IMMUNOLOGICAL TOLERANCE

• ACCEPTANCE OF SELF CELLS

• AUTOIMMUNE DISEASES ARE CAUSED BY THE FAILURE OF IMMUNE

TOLERANCE

• RESULT IN ACTIVATION OF AUTOREACTIVE T CELLS, AND PRODUCTION

OF AUTOANTIBODIES BY B CELLS

• CAUSE INFLAMMATION AND ORGAN DAMAGE

• ALLEVIATED BY CORTICOSTEROIDS AND NSAIDS, INCLUDING ASPIRIN

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ALLERGY

• REFERS TO A GREATLY HEIGHTENED RESPONSE TO A FOREIGN ANTIGEN, OR

ALLERGEN

• MOST COMMON TYPE IS KNOWN AS IMMEDIATE HYPERSENSITIVITY

• RESULTS FROM EXCESSIVE IGE PRODUCTION

• SEASONAL HAY FEVER

• SYSTEMIC ANAPHYLAXIS – SEVERE AND LIFE-THREATENING

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Allergen

Dendritic cell

Helper T cell

Allergen

Helper T cell

B cell

Cytokines (IL-4)

Plasma cell

Mast cell

Allergen

Initial Exposure

Subsequent Exposure

Memory B cell

Receptor for IgEAllergen-

specific IgE

Histamine and

other mediators

of inflammation

are released

Sequence of an

allergic response

ALLERGY

• DELAYED-TYPE HYPERSENSITIVITY PRODUCES SYMPTOMS WITHIN ABOUT 48

HOURS OF A SECOND EXPOSURE TO AN ALLERGEN

• MEDIATED BY TH CELLS AND MACROPHAGES

• CONTACT DERMATITIS

•CAUSED BY VARIED MATERIALS, SUCH AS

POISON IVY, NICKEL IN JEWELRY, AND

COSMETICS

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ANTIBODIES IN MEDICINE

• BLOOD TYPE

• DETERMINED BY ANTIGENS FOUND ON SURFACE OF RED BLOOD CELLS

• ABO BLOOD TYPES – TYPES A, B, AB, AND O

• RH FACTOR – RH POSITIVE AND RH NEGATIVE

• IMMUNE SYSTEM IS TOLERANT OF ITS OWN RBC ANTIGENS, BUT MAKES

ANTIBODIES THAT BIND TO THOSE THAT DIFFER (AGGLUTINATION)

• FOR EXAMPLE, PEOPLE WITH TYPE A BLOOD MAKE ANTIBODIES AGAINST THE B

ANTIGEN

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ANTIBODIES IN MEDICINE

• IN BLOOD TRANSFUSIONS, THE ANTIGENS OF THE DONOR HAVE TO BE

MATCHED TO THE ANTIBODIES OF THE RECIPIENT

• FOR INSTANCE, A TYPE A PERSON CANNOT DONATE TO A TYPE B OR TYPE O

• THESE WOULD HAVE ANTI-A ANTIBODIES

• BLOOD IS TYPED BY AGGLUTINATION REACTIONS, USING CIRCULATING IGM

ANTIBODIES

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EVADING THE IMMUNE SYSTEM

•SOME PATHOGENS CAN ALTER THEIR SURFACE ANTIGENS TO

AVOID IMMUNE SYSTEM DETECTION

• INFLUENZA VIRUS EXPRESSES 2 SURFACE PROTEINS:

HEMAGLUTININ (HA) AND NEURAMINIDASE (NA)

• ANTIGENIC DRIFT – POINT MUTATIONS TO THE HA AND NA GENES

• ANTIGENIC SHIFT – SUDDEN APPEARANCE OF A NEW VIRUS

SUBTYPE WHERE HA AND/OR NA PROTEINS ARE COMPLETELY

DIFFERENT

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EVADING THE IMMUNE SYSTEM

•HIV – HUMAN IMMUNODEFICIENCY VIRUS

•MOUNTS A DIRECT ATTACK ON TH CELLS

• BINDS TO CD4 PROTEINS AND IS ENDOCYTOSED

• AN INDIVIDUAL IS CONSIDERED TO HAVE AIDS WHEN THEIR

TH CELL LEVEL HAS DROPPED SIGNIFICANTLY

• IMMUNOSUPPRESSION RESULTS IN AN INCREASE IN

OPPORTUNISTIC INFECTIONS AND CANCERS

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7600×

© CDC/Science Source/Photo Researchers, Inc.