inoculation
42
Smallpox Since at least the 10th century AD, inoculation
was practiced in China:
! Powdered wound crusts from smallpox victims
were scratched into the skin.
! Smallpox is normally contracted by inhalation
of viral particles in droplets: mortality rate is 2025%
! Inoculation through the skin leads only to
localized infection but the immune system gets
activated and immunological memory is
established.
! The inoculated person will be immune to future
smallpox inhalation.
42
During 1776, George
Washingtons revolutionary army
lost 1,000 men in battle and
10,000 men to smallpox.
On January 6th, 1777, George
Washington ordered his troops to
be inoculated.
The death rate due to smallpox
plummeted afterwards.
In 1783, the American
Revolutionary War was won (by
America).
Today, smallpox is considered
eradicated.
Smallpox inoculation
42
Immunization and vaccination today
Antigens used for immunization or
vaccination must be processed so that they
will provoke an immune response but not
cause disease. There are three principle
ways to do this:
! Attenuation involves reducing the
toxicity of the antigenic molecule or
organism (e.g. adaptation of a virus for
growth in nonhuman cells)
! Biotechnology can produce
recombinant antigenic fragments of
pathogens that activate lymphocytes
but are harmless by themselves.
! DNA vaccines are being developed
that will introduce a gene encoding an
antigen into the body.
42
Polio vaccine
Poliomyelitis, often called polio or infantile paralysis
! Acute viral infectious disease (poliovirus).
! Spread from person-to-person via the fecal-oral route.
! The majority of polio infections are asymptomatic.
! In ~1% of cases the virus enters the central nervous
system. There, the poliovirus infects and destroys
motor neurons. This leads to muscle weakness or
paralysis.
! Polio predominantly affects children.
42
Polio vaccine
In the earlier 20th
century, the USA was
plagued by polio
epidemics.
From 1916 onward, a
polio epidemic appeared
each summer.
The 1952 polio epidemic
was the worst outbreak:
! 58,000 cases
! 3,145 died
! 21,269 were left with
mild to disabling
paralysis.
Iron Lung ward at Rancho Los Amigos Hospital,
Downey, California, ca. 1953
42
Polio vaccine
42
Polio vaccine
42
Polio vaccine
The first effective polio vaccine was developed in 1952 by Jonas Salk at the
University of Pittsburgh.
The Salk vaccine, or inactivated poliovirus vaccine (IPV), is based on
poliovirus grown in a monkey kidney cell line (Vero cell line), which are then
killed with formalin.
The Salk vaccine is injected in the skin.
The Salk vaccine was tested in the largest medical
experiment in history, starting in 1954.
!
!
!
!
!
1.8 million children, in 44 states
440,000 received the vaccine
210,000 children received a placebo (culture media)
1.2 million children received no vaccination
The vaccine was highly effective
42
Polio vaccine
Eight years after Salk's success, Albert Sabin
developed the oral polio vaccine (OPV).
The OPV is a live-attenuated vaccine.
The virus is attenuated because of a random
mutation located in the virus! internal ribosome
entry site.
The attenuated poliovirus replicates efciently in
the gut, the primary site of infection and
replication, but is unable to replicate efciently
within nervous system tissue.
The OPV proved to be superior in
administration, and also provided longer lasting
immunity than the Salk vaccine.
Albert Sabin (1906 - 1993)
Cincinnati Children's Hospital, Ohio
42
Polio vaccine
After the rst vaccine became available, polio cases in the
U.S. dropped by 85-90% in only two years.
The last cases of paralytic polio caused by endemic
transmission of wild virus in the United States were in 1979,
when an outbreak occurred among the Amish in several
Midwest states.
The disease was entirely eradicated in the Americas by
1994.
Movie on polio vaccine
1 min
polio.mov
42
Self Tolerance
The body is tolerant of its own molecules.
Failure to do so results in autoimmune disease.
This self tolerance is based in part on clonal
deletion.
42
Clonal Deletion
Clonal deletion eliminates B or T cells from the
immune system during their differentiation.
In the bone marrow, about 90% of all B cells made are
removed because they react against self antigens.
The same is true for T cells, but the selection occurs
in the thymus.
Elimination is accomplished by means of apoptosis.
42
B Cells: The Humoral Immune Response
B cells are the basic component of the humoral
immune system.
For a B cell to differentiate into a plasma cell, it
must bind an antigenic determinant.
A helper T cell (TH) must also bind the same
determinant as it is presented by an antigenpresenting cell.
Cellular division and differentiation of the B cell is
stimulated by a signal from the activated TH cell.
Activated B cells become plasma cells and
memory cells.
Figure 42.9 Structure of Immunoglobulins (Part 1)
42
Antibodies
Antibody molecules are proteins called
immunoglobulins.
Two identical light chains and two identical heavy chains
make up the tetrameric units.
Disulfide bonds hold the chains together.
Both the light and heavy chains on each peptide have
variable and constant regions.
The constant regions are similar among the
immunoglobulins and determine the class of the
antibody.
42
B Cells: The Humoral Immune Response
The variable regions differ in their amino acid
sequences and are responsible for the diversity of
antibody specificity.
The heavy and light chain variable regions align and
form the binding sites.
Each tetramer has two identical antigen-binding
sites, making the antibody bivalent.
Table 42.3 Antibody Classes (Part 1)
...next slide
Table 42.3 Antibody Classes (Part 2)
Figure 18.11 IgG Antibodies Promote Phagocytosis
Macrophages have Fc
receptors which help
phagocytosis
42
T Cell Receptors
T cells, like B cells, possess specific surface
receptors: T cell receptors
The genes that code for T cell receptors are similar to
those for immunoglobulins.
T cell receptors also have constant and variable
regions.
A major difference between antibodies and T cell
receptors is that T cell receptors bind only to an
antigenic that determinant is displayed on the surface
of an antigen-presenting cell.
Figure 42.11 A T Cell Receptor
42
T Cells: The Cellular Immune Response
Activated T cells give rise to two types of effector cells.
Cytotoxic cells, or TC, (killer T cells) recognize
virus-infected cells and kill them by causing them to
lyse.
Helper T cells, or TH cells, assist both the cellular and
humoral immune systems.
Activated helper T cells proliferate and stimulate both B
and TC cells to divide.
42
Specific / Adaptive Immunity
APC
42
Figure 42.6
The specific immune system
42
T Cell receptors bind only to antigens that are presented by
MHC molecules
What are MHC molecules?
42
The major histocompatibility complex (MHC)
The major histocompatibility complex
(MHC) gene products are plasma membrane
glycoproteins.
MHC proteins display antigens.
There are three classes of MHC proteins (but
well only talk about two): MHC I and MHC II
42
MHC I proteins
Class I MHC proteins are present on the surface of
every nucleated cell in animals.
When cellular proteins are degraded in the proteasome,
an MHC I protein may bind a fragment and travel to the
plasma membrane to present it outside on the cells
plasma membrane surface.
MHC I is a kill me protein.
Figure 18.16 The Interaction between T Cells and Antigen-Presenting Cells (Part 2)
Virus infected
or cancer
cell
42
Cytotoxic T Cells
Foreign protein fragments from proteosome degradation
are bound by class I MHC molecules and carried to the
plasma membrane, where TC cells can check them.
If a cell has been infected by a virus, or has mutated, it
may present protein fragments that are not normally found
in the body.
If a TC cell binds to the MHC Iantigen complex, the TC
cell is activated to proliferate and differentiate (activation
phase).
42
Cytotoxic T Cells
In the effector phase, TC cells once again bind to the
cells bearing MHC Iantigen complex and secrete
molecules that lyse the cell.
TC cells can also bind to a specific target cell receptor
(called Fas).
This binding initiates apoptosis in the target (for
example, virus-infected) cell.
This system helps rid the body of virus-infected cells.
It also helps to destroy some cancer tumors.
Figure 42.13 (b) Phases of the Humoral and Cellular Immune Responses (Part 1)
Figure 42.13 (b) Phases of the Humoral and Cellular Immune Responses (Part 2)
...run animation in Safari: Animation-42-04.swf
Movie:
Cytotoxic T cell
42
MHC-II proteins on professional antigen-presenting cells
Class II MHC proteins are found mostly on the
surface of B cells, macrophages, and other
professional antigen-presenting cells.
When an antigen is phagocytosed by a professional
antigen-presenting cell, it is broken down and
fragments are presented at the cell surface by class II
MHC proteins.
Figure 42.12 Macrophages Are Antigen-Presenting Cells
42
MHC proteins: SUMMARY
42
Activation of the auto-destruct sequence...
Antibody production (humoral response) requires that a
TH cell and a B cell concur.
Activation phase + effector phase
42
The activation phase
A TH cell containing a specific T-cell receptor can
bind to an antigen presented by an antigenpresenting macrophage.
This activates the TH cell: it will proliferate to
produce a clonal population of identical TH cells.
Figure 42.13 (a) Phases of the Humoral and Cellular Immune Responses (Part 1)
42
The effector stage
An antigen of the same sort must also be recognized
by a specific IgM receptor on the surface of a B cell.
The B cell ingests and degrades the antigen and
presents a piece of processed antigen in a class II
MHC protein on its cell surface.
One of the TH cells created in the activation stage
recognizes the processed antigen on the surface of
the B cell.
The TH cell releases cytokines, which activate B cell
proliferation and differentiation into plasma cells and
memory cells.
The plasma cells secrete antibodies.
Figure 42.13 (a) Phases of the Humoral and Cellular Immune Responses (Part 2)
Watch Humoral Response movie
42
The Genetic Basis of Antibody Diversity
Wait a second !
Proteins are encoded by genes.
There are millions of different antibodies but the
human genome has only ~30,000 genes.
It does not compute!!!
42
The Genetic Basis of Antibody Diversity
Here is the trick:
There are only a few antibody genes in the
genome.
But B cells can shuffle (recombine) them which
can generate millions of new combinations.
42
The Genetic Basis of Antibody Diversity
Each gene encoding an immunoglobin is in reality a
supergene assembled from several clusters of smaller
genes located along part of a chromosome.
During B cell development, these variable regions
rearrange and join.
Pieces of DNA are deleted, and DNA segments formerly
distant from one another are joined together.
Immunoglobulin genes are assembled from randomly
selected pieces of DNA.
42
Heavy chain genes
42
The Genetic Basis of Antibody Diversity
There are multiple genes coding for each of the four
kinds of segments in the polypeptide chain for the
heavy chain in mice: 100 V, 30 D, 6 J, and 8 C regions.
Each B cell randomly selects one gene for each of the
V, D, J, and C regions.
A similar process occurs for the light chain.
Theoretically, there are 144,000 x 144,000 possible
combinations of light and heavy chains, i.e, 21 billion
possibilities.
Watch Antibody Formation movie
42
The Genetic Basis of Antibody Diversity
Additional diversity is possible because the
recombinations do not occur at precise segments.
Imprecise recombinations can create new codons at
the junctions.
After DNA fragments are cut out and before they are
joined, an enzyme, terminal transferase, adds some
nucleotides to the free end. This adds even more
variability by causing frame shifts and new codons.
Finally, the relatively high mutation rate in
immunoglobulin genes leads to even more diversity.
42
Autoimmune diseases
If clonal deletion fails, forbidden clones of B and T
cells directed against self-antigens are sometimes
made.
Examples of autoimmune diseases include:
! Systemic lupus erythematosis
! Rheumatoid arthritis
! Multiple sclerosis
! Insulin-dependent (Type 1) diabetes mellitus