Transcript Document

Immune
System
Notes
I. Critical Vocabulary
A. Immune System: a set of glands, tissues, cells, and dissolved
proteins that combine to defend against “non-self” entities
B. Antigen: any “non-self” chemical that triggers an immune
system response. Antigens are often naturally occurring
molecules (protein, glycoprotein, or polysaccharide) on the
surface of cells and viruses
C. Pathogen: any antigen that causes a disruption in homeostasis a.k.a. normal, disease free, functions
D. Antibody: a protein produced specifically in response to the
presence of an antigen - neutralizes antigen by bonding to the
antigen
E. White Blood Cells (wbc’s): a set of cells called lymphocytes, that
free-float in the blood and lymph fluid - active in the immune
system
II. Immune System Response Overview
Antigen
("non-self" entity)
celluar, viral, other
Specific Response
(humoral)
via the production
of antibodies
Memory
Response
Non-Specific Response
Specific Response
(cell mediated)
via the destruction
of infected cells
Memory
Response
III. Non-Specific Response
(first line of defense)
A.
The Skin
1. pH: 3-5
2. normal bacterial flora
B.
Mucous Membranes
ex: respiratory and digestive tracts
C.
Specialized phagocytic white blood cells (wbc’s) that perform
phagocytosis = “cell eating”
ex: Macrophages: large amoeboid cells, that consume “nonself” cellular or non-cellular material
D.
Antimicrobial Protein
ex: complement proteins: cell lysing activity
E.
Inflammatory Response
1. vasodialation: blood vessels become more permeable
2. complement proteins attract phagocytes
3. macrophages consume pathogens and related debris
4. high fever triggered by chemicals released by wbc’s
IV. Cell Surface Molecular Markers
A. Major Histocompatibility Complex (MHC)
1. recognition mechanism
a. distinguish self from non-self
2. set of 20 genes w/100 alleles for each gene
3. MHC genes code for glycoproteins embedded in the plasma
membrane
a. cells use to detect the immediate environment
4. virtually impossible for two individuals to have the
matching set of MHC markers, except identical twins
5. two classes of MHC molecules
a. class I MHC: all nucleated cells
b. class II MHC: lymphocytes (macrophages, B and T cells)
V. Humoral Response (specific)
A. Specificity
ex: produces antibodies in response to non-self entities such as
toxins, free bacteria and viruses
B. Cells Involved (lymphocytes - active form called effector cells)
1. B-cells
a. originate and mature in bone marrow
b. activated B-cells become plasma cells and secrete
antibodies  the point of the humoral response!
c. humoral response only
2. T-cells
a. originate in bone marrow - mature in the Thymus gland
b. of the three types, only helper (TH) T-cells participate in
the humoral response
C. Activation of B-cells (two types of activation)
1. Clonal selection
a. B-cells directly stimulated to secrete antibodies
b. large number of different B-cells
1. pre-determined during embryonic development
c. antigen receptors (in the form of antibodies) on the surface
of B-cells bind to free-floating antigens
1. based on antigen-receptor specificity
d. once the antigen is bound to the receptor, the B-cell is
stimulated to clone itself (millions of times over)
* activated immune system cells are called effector cells
1. first type of clone: plasma cells: secrete antibodies
2. second type of clone: memory B-cells (details later)
e. antibodies secreted into the blood and lymph bind to the
original antigen *tagging the antigen for consumption by
a phagocyte
Clonal
Selection
Figure
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
43.6
Pg. 905
special note: the captions in the textbook for this graphic are important to review
Clonal Selection
click here for video
animation
2. T-dependent
a. antigen binds to specific antigen-receptor on a macrophage
1. t-dependent antigen (cannot directly stimulate B-cells)
b. involves macrophages and TH cells
c. macrophage consumes the pathogen
1. in the dermis and in mucous membranes the most
prevalent macrophage is a dendritic cell
d. antigen fragments bind to MHC II proteins and are
presented on the surface of the macrophage
e. CD4 receptors on TH cell bind to antigen/MHC II complex
f. Th are activated, become effector cells and form clones
g. activated TH secrete cytokines which stimulate B-cells
h. effector B-cells form clones: antibody secreting plasma cells
i. most antigens are T-dependent
Fig 43.13 - pg. 911
B-Cell Activation
Due to
T-Cell Dependent
antigen
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
special note: the captions in the textbook for this graphic are important to review
VI. Molecular Basis of Antigen-Antibody
Specificity
A. Antibodies do not generally recognize antigens as a whole
1. epitope: small, specific regions of the antigen’s structure
that fit into the antigen-binding site of the antibody
B. A given antigen may have multiple epitopes on its surface
 multiple antibodies may bind to the same antigen
C. Antibodies are proteins called immunoglobulins (Igs)
1. Y-shaped w/4 polypeptide chains
2. do not directly destroy pathogens
3. antibodies block viral attachment site, or bacterial toxin
4. antigen-antibody complex tags pathogen for destruction by
a macrophage
Humoral and Antibody-Antigen Graphics
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Fig. 43.14
Fig. 43.15
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
click here for
video
Fig. 43.16
VII. Cell Mediated Response (specific)
A. Specificity
1. produces cytotoxic T-cells (TC) which attack and destroy
infected cells and cancer cells
a. many pathogens, including ALL viruses, are obligate
intracellular parasites
B. Activation of TC cells
1. intracellular parasites are consumed by macrophage
2. MHC II-Antigen complex is recognized by CD4 TH cell
3. TH cell secretes a cytokine called Interleukin-2 which activates TC and Bcells
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Fig. 43.11
C. Active TC cells (effector cell - following stimulation by Interl-2)
1. effector TC cells are called CD8 cells - named for the CD8
protein associated with the T-cell receptor protein
2. infected host cells present pathogenic antigens embedded in a
MHC I protein on its surface (recall all nucleated cells have)
3. T-cell receptor binds with MHC I-Antigen complex with help
from the CD8 protein
4. TC cell secretes the protein perforin which lyses the infected
cell -or- the cancer cell
5. effector TC can bind to and destroy multiple cells.
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Fig.
43.12(a)
A cytotoxic
T-cell (Tc)
that has
already lysed a
cancer cell
Figure
43.12
Quic kTime™ and a
TIFF ( LZW) dec ompres s or
are needed to s ee this pic ture.
VIII. Secondary Immune Response/Memory
A. Result of exposure to previously encountered antigen
1. 3-5 day response time vs. 5-10 day primary response
2. immunity lasts longer
3. antibodies produced are more effective
B. Performed by memory cells
1. produced during 1˚ response
2. not active during 1˚ response
3. activated by the original antigen
4. when activated - rapid proliferation to form newly cloned
effector cells and, in some cases, more memory cells.
Fig. 43.7 Immunological Memory
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
IX. Suppressor T cells (TS)
A. Function to suppress the immune system when the antigen in
question is no longer present
B. TS are not well understood.
C. May be effective in stopping a immune response through
hormonal secretions.
X. Acquired Immunity
A. Active Acquired Immunity
1. dependent on person’s own immune system
2. based on non-disease causing antigens that stimulate an
immune response
3. acquired via vaccines or blood transfusions (rare)
B. Passive Acquired Immunity
1. transferred from one person to another
a. mother to fetus
b. mother to baby via mothers milk
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Fig. 43.10 Summary of the Immune Responses