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Adaptive Immunity

Chapter 17

BIO 220

Adaptive Immunity

• Adaptive defenses acquired through infection or vaccination

• Specificity for particular pathogen

• Memory for most previously encountered antigens

• Ability to distinguish “self” from “not self”

B and T lymphocytes

Fig. 17.1

Immunocompetence

• This is the ability to carry out adaptive immune responses

• Selective process

• In an immunocompetent lymphocyte, specific proteins are inserted into the plasma membrane of that cell

• Antigen receptors (B & T)

• CD4 (T)

• CD8 (T)

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Role of cytokines in adaptive immunity

• Cytokines are chemical messengers composed

of proteins or glycoproteins

– Interleukins (communication between leukocytes)

– Chemokines (movement of leukocytes to areas of

injury or infection)

– Interferons

– Tumor necrosis factor (inflammatory reactions)

– Hematopoietic cytokines (controls formation of

formed elements from stem cells)

Antigens

• Substances that cause the production of antibodies

• Microbial antigens are typically proteins or large polysaccharides that are components of microbe capsules, cell walls, flagella, fimbriae, toxins, viral coats, or other microbial surfaces

• Complete antigens can induce an immune response leading to production of antibodies, which can then bind the antigen

• Usually antibodies recognize and interact with specific regions on antigens called epitopes(antigenic determinants)

Epitopes

Fig. 17.2

Remember PAMPs?

Haptens

• These are incomplete antigens

• Foreign substance with a low molecular weight (< 10,000) is not antigenic unless it is attached to a carrier molecule

• Once an antibody has been formed against a hapten, the antibody will react with the hapten regardless of whether or not the carrier protein is present

• i.e. Penicillin

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Hapten Example: Chemical in Poison Ivy

Antigen-Presenting Cells (APCs)

• B cells

• Dendritic cells

• Macrophages

Figs. 17.10, 17.11

Types of Adaptive Immunity

Cell-Mediated

• T cells

• Effective against

– Intracellular pathogens

like bacteria, viruses, or

fungi

– Cancer cells

– Foreign tissue implants

Antibody-Mediated

(Humoral)

• B & T cells

• Antibody production

• Effective against

– Extracellular pathogens

(mostly bacteria,

bacterial toxins, viruses)

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Cell-Mediated Immunity

Players in cell-mediated immunity

• Antigen-presenting cells

– Macrophages & dendritic cells

• Helper T cells

– TH1

• Cytotoxic T cells

• Infected body cells

• Pathogens entering the

GI tract are transported

through M cells to

Peyer’s patches.

• Within Peyer’s patches

the antigens will be

exposed to APCs and

lymphocytes.

Fig. 17.9

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APCs at work

Fig. 17.12 Fig. 17.13

The result of helper T

cell activation is clonal

expansion.

Activation of cytotoxic T cells

Fig. 17.14

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22_17 Apoptosis

Fig. 17.15

Fig. 17.20

Natural killer cells (NKCs)

• Can also destroy certain virus – infected cells

and tumor cells

– If MHC Type I molecules are missing on cell, NKCs

destroy cell

• Can also attack parasites

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Antibody - dependent

cell - mediated toxicity

• Large pathogens like

protozoa or helminthes

are coated with

antibodies

• Eosinophils, macrophages,

NK cells bind to antibodies

• Ultimately target cells are

lysed

Fig. 17.16

Antibody-Mediated Immunity

Players in Antibody-mediated immunity

• Antigen-presenting cells

• Helper T cells

– TH2

• B cells

• Plasma cells

APCs at work

Fig. 17.12

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Fig. 17.13

The result of helper T

cell activation is clonal

expansion.

Activation of B cells

• Binding of T-independent

antigens may activate B

cells, or

• B cells may process T-

dependent antigens

• Helper T cells co-

stimulation by interleukin-

2 or other cytokines

Antibody-mediated immunity(T dependent antigens)

Fig. 17.5

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The result of B cell

activation is clonal

expansion.

Fig. 17.20

Antibody structure

Fig. 17.4

Fig. 17.8

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Immunologic memory

Fig. 17.17

Types of adaptive immunity

Fig. 17.18