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Immune system
Haixu Tang
School of Informatics
Human lymphoid organs
Lymphocytes are required for
adaptive immune responses to
foreign antigens
Innate immune system helps
activate the adaptive immune
system
The development and activation of
T and B cells
The clonal selection theory
Primary and secondary antibody
responses
Cellular basis of immunological
memory
Induction of immunological
tolerance
B cell activation
Innate and adaptive immune
responses
An antibody molecule
Antibody-antigen interactions
The hinge region of an antibody
molecule
A pentameric IgM molecule
Antibody-activated phagocytosis
There Are Five Classes of Heavy
Chains
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IgM, which has μ heavy chains, is always the first class of
antibody made by a developing B cell;
After leaving the bone marrow, the B cell starts to produce cellsurface IgD molecules as well, with the same antigen-binding site
as the IgM molecules.
The major class of immunoglobulin in the blood is IgG, which is a
four-chain monomer produced in large quantities during
secondary immune responses;
IgA is the principal class of antibody in secretions, including
saliva, tears, milk, and respiratory and intestinal secretions;
The tail region of IgE molecules, which are four-chain monomers,
binds with unusually high affinity (Ka ~ 1010 liters/mole) to yet
another class of Fc receptors;
Antigen binding to antibody
Constant and variable regions
The gene of an antibody heavy
chain
3D structure of antibody
Antigen-binding sites of antibodies
DNA is rearranged during B cell
development
The V-J joining process
The human heavy-chain genesegment pool
The four main mechanisms of
antibody diversification
Antibody gene-pool selection in B
cell development
The two main classes of adaptive
immune responses
DNA rearrangement that occurs in
class switch recombination
T cell responses differ from B cell
responses in two crucial ways
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T cells are activated by foreign antigen to proliferate and
differentiate into effector cells only when the antigen is
displayed on the surface of antigen-presenting cells in
peripheral lymphoid organs. Whereas B cells recognize
intact antigen, T cells recognize fragments of protein
antigens that have been partly degraded inside the antigenpresenting cell. The peptide fragments are then carried to
the surface of the presenting cell on special molecules
called MHC proteins;
The second difference is that, once activated, effector T
cells act only at short range, either within a secondary
lymphoid organ or after they have migrated into a site of
infection. They interact directly with another cell in the body,
which they either kill or signal in some way. Activated B
Two main classes of T cells
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Effector cytotoxic T cells directly kill cells that
are infected with a virus or some other
intracellular pathogen.
Effector helper T cells, by contrast, help
stimulate the responses of other cellsmainly
macrophages, B cells, and cytotoxic T cells
T cell receptor heterodimer
Activation of a T cell
Cytotoxic T cells kill their target
cells
Differentiation of naïve helper T cells into
either TH1 or TH2 effector helper cells
Recognition by T cells of foreign
peptides bound to MHC proteins
Class I and class II MHC proteins
Human MHC genes
A peptide bound in the groove of a
class I MHC protein
A peptide bound in the groove of a
class II MHC protein
The interaction of a T cell receptor with a
viral peptide bound to a class I MHC
protein
CD4 and CD8 co-receptors on the
surface of T cells
An effector cytotoxic T cell recognizes
some aspect of the surface of the host
target cell
The processing of a viral protein
for presentation to cytotoxic T cells
The processing of an extracellular protein
antigen for presentation to a helper T cell
Positive and negative selection in
the thymus
The two signals that activate a
helper T cell
The signaling events initiated by the
binding of peptide-MHC complexes to T
cell receptors
The stimulation of T cells by IL-2 in culture
The activation of TH1 and TH2
cells
Signaling events activated by the
binding of antigen to B cell receptors
(signal I)
The influence of B cell coreceptors on the effectiveness of
signal I
Comparison of the signals
required to activate a helper T cell
and a B cell