Immunity
Chapter 39
Innate vs Acquired
-All animals have innate systems, only vertebrates
have acquired (we will look at mammal aquired)
-acquired develops over a lifetime and is specific
Three Lines of Defense
• Barriers at body surfaces (which technically
is nonspecific)
• Nonspecific responses
• Immune responses - specific
I. Surface Barriers – 1st line of defense
A. skin i. pathogens can’t get through, not good conditions for
growth of pathogens (low moisture, low pH and thick layer
of dead cells) and harmless bacteria present - pathogens
can’t compete
B. Mucous membranes
i. Sticky, helpful bacteria found here, chemicals (like
lysozyme that digest cell wall of bacteria) are present
C. lungs
i. air rushes in and flings pathogens into mucus coated
walls, chemicals (like lysozyme, digest cell wall of
bacteria), and cilia to move pathogens out
D. flushing effect – most of these fluids also contain chemical like
lysozyme or have a non-neutral pH
i. tears, saliva, gastric fluid, urine, etc
The first line of defense in
the respriratory tract
(trachea). The orange cells
produce mucus that that
traps micro-organisms that
enter. The yellow cells are
cilliated which beat in
unison to expel mucus and
trapped microorganisms
upward to pharynx.
Nonspecific Responses
• Lymph nodes trap and kill
pathogens
• Natural killer cells attack a
range of targets
• Inflammation
• Complement proteins
Acute Inflammation
• Nonspecific response to foreign invasion, tissue
damage, or both
• Destroys invaders, removes debris, and prepares
area for healing
• Characterized by redness, swelling, warmth, and
pain (see chart, page 690)
– Caused by the release of histamine from mast cells
which triggers vasodilation and capillary permeability
Inflammation
•
•
•
•
Mast cells and basophils release histamine
Capillaries dilate and leak
Complement proteins attack bacteria
White cells attack invaders and clean up
Figure 39.5
Page 691
The Inflammatory Response
Complement System
• Plasma proteins that take part in both specific and
nonspecific response
• Activation of one triggers cascade of reactions that
activate others
• some insert into plasma membranes of pathogens and
initiate lysis
• some promote inflammation
• some form concentration gradients that phagocytic white
blood cells follow
• some bind to the surface of invaders, marking them for
phagocytosis
3. Complement proteins(approx. 20-30 proteins)
a.) Directly- form protein rings on bacteria membranes
forming pores, water rushes in, bursts cells
b.) Indirectly- The complement protein
coats the surface bacteria. There are
recognition sites on the phaggocytes that
bind with proteins coating the bacteria.
The phagocytes engulf the bacteria in a
process called opsonization-
Features of Specific Immune Responses
• self/nonself recognition – B and T cells
ignore the bodies own cells, self markers on
the organisms own cells
• specificity – B and T cells attack specific
foreign agents
• diversity - B and T cell receptors have the
potential to respond to a billion specific
threats
• memory – a portion of B and T cells are set
aside for future battles with specific agent
Cells of the Immune System
• B-lymphocytes
– Carry out the humoral
immune response
– Circulate in body fluids
– Mature in the bone marrow
• T-lymphocytes
– Carry out the cell-mediated
immune response
– Guards against invaders
within the cell
– Mature in the thymus
Antigens
• “Nonself” markers on foreign agents and
altered body cells such as tumors
• Trigger division of B and T cells
• When a B or T cell is stimulated to divide, it
produces more than one cell type
• Memory cells - set aside for future use
• Effector cells - engage and destroy the
current threat
Steps in Immune Response
• Recognition of an antigen
• Rounds of cell division that form huge populations of
lymphocytes
• Specialization of lymphocytes into effector and memory
cells that have receptors for one kind of antigen
• 2 types of responses
– Antibody mediated – extracellular targets, B cell
– Cell mediated – intracellular or altered body cell targets,
cytotoxic T cells
• Both are triggered by helper T cells
Lymphocyte Battlegrounds
• Lymph nodes filter antigens from
body fluids
• Macrophages, dendritic cells, B
and T cells in nodes and spleen
mount a defense
Humoral and Cell-Mediated Immunity
• Humoral Immunity
– Antibodies circulate as soluble proteins in
blood plasma and lymph
– Defend against toxins, free bacteria, viruses
in body fluids
• Cell-mediated Immunity
– White blood cells are active against bacteria
and viruses inside the host’s cells and
against fungi, protozoa, and worms
Antibody-Mediated Response
• Carried out by B cells
• Targets are extracellular pathogens and
toxins
• Antibodies bind to target and mark it for
destruction by phagocytes and
complement
Antibody-Mediated Response
• B cell becomes
antigen-presenting
cell
• Helper T cell binds
to antigen-MHC
complex
• Interleukins
stimulate B cell
division and
differentiation
• Effector cells
secrete antibodies
antigen
naïve
B cell
Figure 39.14
Page 697
MHC molecule
antigenMHC
complex
helper
T cell
antigenpresenting
B cell
interleukins
memory
B cell
antibody
effector
B cell
Antibodies are proteins made of 4 polypeptides. 2 identical, heavy, polypeptide
chains and 2 identical, light polypeptide
chains. A light chain is bonded to a
heavy chain by disulfide bonds.
Five Different Classes of
AB
-IgG- monomer- found
late in response crosses
placenta
-IgA- Dimer and
monomer form
-IgM- pentamermonomer form helps
with virgin B cells
-IgD- monomers found
surface B cells
-IgE- monomer found
in area with connective
tissue helps with
release histamine
Cell-Mediated
Response
one
macrophage
another
macrophage
• Carried out by T cells
• Stimulated by antigenpresenting
macrophages
• Main target is antigenpresenting body cells
(cells with intracellular
pathogens) or tumor
cells
interleukins
cytotoxic interleukins
T cell
helper T
cell
infected
body cell
Figure 39.15
Page 698
Recognition
Each of us are unique because of
differences on surface proteins.
Chromosome 6 (Major
Histocompata-bility Complex or
MHC genes) has several hundred
genes that code for these surface
proteins or MHC proteins (classes I
&II)
There are 3 major groups of MHC
proteins
Class I, II, and III:
Class I MHC proteins are on all cells
Class II MHC proteins are found on
1. macrophages, 2. B cells ,3. T cells
Class III MHC proteins form the
complement proteins
During fetal development cells will be
labeled Class I and/or Class II proteinsthe MHC proteins act like a badge to
identify you as you. These MHC
proteins makes sure that your immune
system does not attack you.
Role of T cells
T- have two receptor sites one for the
MHC protein and one for an AG
During development T-cells get their MHC
recognition site- must match the body's
own MHC proteins. If they do not make a
match they die. If they do, they become
MHC restricted.
Now, if recognition site matches a Class I
protein (found on all cells) the T- cell
becomes cytotoxic (killer) cell.
If recognition site matches a Class II
protein (T cells or macrophage), the Tcell will become a helper-T-cell.
These cells are MHC restricted and are
called virgin-T-cells.
Clonal Selection
• Each antigen, by binding to specific
receptors, selectively activates a tiny
fraction of cells from the body’s diverse
pool of lymphocytes
• This relatively small number of selected
cells gives rise to a clone of millions of
effector cells, all dedicated to
eliminating the specific antigen that
stimulated the immune response
Clonal Selection
Colonal selection works 2 ways
I. Arousal of T cells
II. Direct arousal of B cells by AG
I. Arousal of T cells
1. Macrophages(have both MHCI and MCHII
proteins)
2. Macrophage goes to the site of infection
3. The macrophage devours virus, AG, or
bacteria and the macrophage then puts bits and
pieces of invader on cell membrane(assoc.
w/MHCI and MHCII proteins)
Now the macrophage goes to the virgin Tcells looking for a match between the the
MHC receptor and antigen receptor on the Tcell and the MCH protein and antigen on the
macrophage.
When the macrophage binds with virgin Tcell a substance called interluken is secreted.
Interluken causes T-cells to reproduce
making either cytotoxic T-cells, T-memory
cells, or helper T-cells.
Activated cytotoxic cells go
around frisking cells with its
dual receptor site. If cell is
healthy, then it will only have
MHCI protein on surface, and
the cytotoxic cell will ignore it,
going on its way. However, if
cell is infected, the cell will
have bits of AG on its surface
with the MHCI receptor site.
The cytotoxic T cell
will put holes in
infected cells water
rushes in and kills the
cell. The cell dies and
phagocytes appear to
clean up mess.
*Cytotoxic cells also kill cancer
cells because cancer cells
change and have new surface
proteins. Every once in a while
the cells will escape the
cytotoxic-T-cell because the
MHCI protein has also changed
*There is no longer a dual
match and cells replicate or
metastisize
A cytotoxic cell (orange)
destroying a cancer cell
(purple).
II. Arousal of B cells and antibody formation.
Activated helper-T- cells act much like the
macrophage did in activating virgin B cells
1. Virgin B cells has AB on surface. It captures
free floating AG.
2. The B-cell puts AG next to MHCII protein.
3. Helper-T-cell with its MCH II recognition site and
antigen recognition site finds B-cell with AG and
MHCII protein
4. The two join and the helper-T-cell
secretes interleuken. This causes the
B-cell to reproduce.
5. The B-cells fall into 2 types
a. Memory-B-cells for the
secondary immune response
b. Plasma cells which will produce
REMEMBER WHAT ANTIBODIES
CAN DO!!!!!!!!!!!!!!!!!!!!!!!!!! They
are AG specific.
*AB 1. Bind to several AG
2. Can trigger complement
holes in the cell
3. Opsonization - to increase
the susceptibility of (bacteria) to
ingestion by phagocytes.
monoclonal antibody
antibody produced by a laboratory-grown cell
clone, either of a hybridoma (a hybrid cell made
in the laboratory by fusing a normal cell with a
cancer cell) or a virus-transformed lymphocyte,
that is more abundant and uniform than natural
antibody and is able to bind specifically to a
single site on almost any chosen antigen or
reveal previously unknown antigen sites: used
as an analytic tool in scientific research and
medical diagnosis and potentially important in
the treatment of certain diseases. Abbreviation:
Mab
Immunization
• Process that promotes immunity
• Active immunization – Antigen-containing material is injected
– Confers long-lasting immunity
• Passive -
– Purified antibody is injected
– Protection is short lived
•Allergies
A. a normally harmless substances provoke inflammation,
excess mucus secretion and sometimes and immune reponse
•Disorders
A. Autoimmune – self-recognition fails and the immune
system attacks it own body components
B. Deficient Immune Response – loss of immune function
i. primary – present at birth, due to altered genes or
abnormal development
ii. secondary – loss of immune function following
exposure to outside agents (AIDS)
-AIDS/HIV – attacks helper T cells
A T-cell
being
infected by
the aids
virus (blue
particles)
-nonspecific
-Barriers movie
-2nd line of defense (part a)
-2nd line of defense (part b)
-specific defense
-3rd line part a
-3rd line part b
-3rd line part c
-3rd line part d
-cell mediated response animation
-humoral (antibody) response