Transcript Immunology Review

Immunology Review
Part One
Immune Responses
Innate Immunity
• First line of defense
in preventing foreign
substances from
entering body.
• Available at birth
(innate or natural).
• Generalized,
nonspecific reaction.
Innate Immunity
• No prior exposure to foreign substance
required.
• Response doesn’t change with further
exposure.
• Influenced by:
– Age
– Stress
– Fatigue
– Nutritional status
Elements Of Innate Immunity
• Skin
• Tears, saliva,
secretions
• Mucus
• Chemicals
• pH
•
•
•
•
•
•
Normal flora
Temperature
Cough Reflex
Toll-like receptors
Phagocytes
Inflammation
Phagocytosis
• Monocyte, macrophage, eosinophil or neutrophil drawn
in to area by chemotactic factors such as complement or
cytokines.
• Receptors on phagocyte make contact with foreign
material.
– May be enhanced by CRP, complement or antibodies.
(Opsonins)
• Phagocyte engulfs foreign material to form phagosome.
• Phagosome merges with granules in cytoplasm.
Granules contain chemicals that digest foreign material.
• Waste material is expelled from phagocyte (exocytosis).
Inflammation
• Capillaries dilate and blood accumulates in
the affected area, leading to redness and
increased temperature.
• Fluid accumulates, causing edema.
• Phagocytes migrate into the tissue and
destroy foreign invaders.
Cells Alive!
• To see the interaction between elements
of innate immunity, please go to
http://www.cellsalive.com/ouch1.htm
• View “Anatomy of a Splinter”.
Acquired (Adaptive) Immunity
• Forms only after exposure to foreign
substance.
• Response is specific to the foreign
stimulus.
• Recognizes self vs. non-self.
• Displays memory.
• 2 forms:
– Cell mediated
– Humoral
Cell Mediated Immunity
Cell Mediated Immunity
• Controlled by T lymphocytes.
– Influence other parts of the immune system
(including the humoral response) through the
release of cytokines.
• Responsible for such processes as
delayed hypersensitivity, transplant
immunity, and tumor rejection.
Cell Mediated Process
• Foreign matter is broken down into
smaller peptides.
• Peptides combine with the Major
Histocompatibility Complex (MCH)
antigens.
Major Histocompatibility Complex
• Found on the membrane of every nucleated cell.
• Three classes:
– I (A, B, C loci)
– II (DR, DQ, DP loci)
– III (complement , Tumor Necrosis Factor [TNF])
• MHC Class I and II antigens each have an
antigen binding groove which carries foreign
peptides.
Major Histocompatibility Complex
Class II
Class I
Antigen
Binding
Groove
Antigen
Binding
Groove
Pathogen Recognition
• MHC Class I antigens are found on
almost every nucleated cell in the body
• These antigens bind peptides that are
produced within the cell
– Tumors, viruses, intracellular bacteria
– These peptides are termed endogenous
antigens
Pathogen Recognition
• MHC Class II molecules are found on
monocytes, macrophages, dendritic cells, and
B lymphocytes.
– Termed Antigen Presenting Cells (APC)
• Class II molecules bind foreign peptides that
come from bacteria, virus, or parasites that
have been ingested by the APC.
– Termed exogenous antigens
Pathogen Recognition
• T cells possess receptors (TCR) that recognize
foreign antigen when it is bound to MHC antigen.
– T cytotoxic lymphocytes (Tc cells) interact with Class I antigens.
– T helper lymphocytes (TH cells) interact with Class II antigens.
• TCR is coupled to CD3.
• CD3 signals the interior of the T cell that antigen is
present.
• T cell then secretes cytokines that effect
surrounding cells.
• Some T cells mature into memory T cells. These
assist with rapid recognition of the foreign antigen
the next time it is encountered, thus speeding up the
immune response.
T Lymphocyte Subsets
• T helper cells (TH)
–
–
–
–
Make up 2/3’s of the T lymphocyte population
CD4 positive
React with MHC class II proteins
Stimulate both the cytotoxic and the humoral
responses
• T cytotoxic cells (TC)
– CD8 positive
– React with MHC class I proteins
Cytotoxic T Cells
• TC cell recognizes the foreign peptides
associated with the Class I MHC antigen.
– Recognition via the TCR and CD8.
• TC produces perforin, a protein that causes
disruption of the membrane of the affected cell.
• The affected cell dies by apoptosis.
– Cell fragments into smaller particles.
– Fragments are engulfed by phagocytes.
• Cytokines TNF and interferon are released by
the TC to prevent spread of virus.
– May injure healthy tissue.
Cells Alive!
• Please go to
http://www.cellsalive.com/ctl.htm
• View “The Cytotoxic T Lymphocyte”.
Humoral Immunity
Humoral Immunity
• Major cell involved is the B cell.
• Develops into plasma cells and memory
cells.
• Influenced by T helper cells.
The Humoral Process
• Foreign antigen is introduced to host.
• Antigen Presenting Cells (APCs) process
antigen into peptide fragments, then present it
to the TH lymphocyte.
– Dendritic cells and macrophages function as APCs
– Foreign peptides bind to MHC Class II antigens
• The TH recognizes the foreign antigen through
its T Cell Receptor (TCR) and CD4.
The Humoral Process
• The B cell has also recognized the foreign
antigen via the B cell receptor (BCR), and
processed the foreign antigen.
– Foreign peptide is then expressed on the
surface MHC class II molecules.
• TH recognizes that the peptide seen by its
TCR and the peptide presented by the B
cell are the same.
• TH releases cytokines to stimulate B cell.
The Humoral Process
• B cells divide into plasma cells or memory cells.
– Plasma cells produce and secrete antibody.
– The antibody produced is specific for one
antigenic determinant!
– Memory cells recall previous encounter with foreign
antigen. Persist in circulating lymphocyte pool for
months up to years.
Cells Alive!
• Please go to
http://www.cellsalive.com/antibody.htm
• View “Making Antibodies”.
The Humoral Process
• Signals from the TH influence the class of
antibody produced by the B cell and the ability to
switch immunoglobulin classes.
– Interleukins
– Transforming growth factor
• IgM is the first immunoglobulin produced.
• Most B cells switch from IgM production to IgG,
the most prevalent immunoglobulin.
Primary vs. Secondary Humoral
Response
IgG
IgM
IgM
IgG
First
exposure
to antigen
Second & subsequent
exposures to the same
antigen
Primary Response
• First time the host encounters the
foreign antigen.
• Latency period: Lag time between
exposure to antigen and production of
antibodies.
• IgM is the main class of antibody
(immunoglobulin) produced.
– Some IgG is made.
Primary Response
• Concentration of antibody (titer) is
relatively low.
• Antibody titer drops off quickly.
Secondary Response
• Also called the anamnestic or memory
response.
• A repeat encounter with the same
foreign antigen.
• Usually takes a smaller dose of antigen
to stimulate the response.
• Memory cells hasten the immune
response.
Secondary Response
• IgG is the primary immunoglobulin
produced.
– Some IgM is also made.
• Response is faster.
• Antibody titer is higher.
• Antibody detectable for a longer
period of time.
Secondary Response
Faster, Higher, Stronger, Longer
This concludes “Immunology Review,
Part One: Immune Responses”
Please
complete the
exercise
“Comparing
Immune
Response
Mechanisms”