The Immune System

Page
8

Binding to a class I MHC complex on an infected cell activates a cytotoxic T cell and makes it an active killer.

The activated cytotoxic T cell secretes proteins that destroy the infected target cell.

Slide 47

The killing action of cytotoxic T cells

Cytotoxic T cell

Perforin

Granzymes

TCR

CD8

Class I MHC

molecule

Target

cell

Peptide

antigen

Pore

Released cytotoxic T cell

Dying target cell

1.

2.

3. lysis

Slide 48

B Cells: A Response to Extracellular Pathogens

The humoral response is characterized by secretion of antibodies by B cells.

Activation of B cells is aided by cytokines and antigen binding to helper T cells.

Clonal selection of B cells generates antibody-secreting plasma cells, the effector cells of humoral immunity. Positive Feedback …

Slide 49

B cell activation in the humoral immune response

Antigen-presenting cell

Endoplasmic

reticulum of

plasma cell

Secreted

antibody

molecules

Bacterium

B cell

Peptide

antigen

Class II MHC

molecule

TCR

CD4

Helper T cell

Activated

helper T cell

Cytokines

Clone of memory

B cells

Clone of plasma cells

2 µm

+

Slide 50

Antibody Classes

The five major classes of antibodies, or immunoglobulins, differ in distribution and function.

Polyclonal antibodies are the products of many different clones of B cells following exposure to a microbial antigen.

Monoclonal antibodies are prepared from a single clone of B cells grown in culture.

Slide 51

The five antibody, or immunoglobulin (Ig), classes

Class of Immuno-

globulin (Antibody)

IgG

(monomer)

IgM

(pentamer)

J chain

IgA

(dimer)

IgE

(monomer)

IgD

(monomer)

Trans-

membrane

region

J chain

Secretory

component

Distribution

Function

First Ig class

produced after

initial exposure to

antigen; then its

concentration in

the blood declines

Promotes neutraliza-

tion and cross-

linking of antigens;

very effective in

complement system

activation

Present in

secretions such

as tears, saliva,

mucus, and

breast milk

Only Ig class that

crosses placenta,

thus conferring

passive immunity

on fetus

Triggers release from

mast cells and

basophils of hista-

mine and other

chemicals that cause

allergic reactions

Present primarily