Download Immune System Notes: Part I

Immune System Notes: Part I
The body protects itself by using three lines of defense…
I. 1st Line of Defense: Non-specific body defenses
A. Surface membrane barriers
 Skin has keratin filled cells used as barriers
 Sweat and vaginal secretions are acidic(pH of 3-5)
 Saliva and tears have an enzyme called lysozyme
which kills bacteria by breaking down the cell walls of
bacteria
 Sticky mucous in nose and throat trap invaders and
cilia sweeps them up to be coughed or sneezed out
 Gastric juice of the stomach kills most microbes
II.2nd Line of Defense: Cells and Chemical Defenses
A. Non-specific cells
 Phagocytes are white blood cells (leukocytes) that
engulf pathogens by phagocytosis. Monocytes (which
become macrophages) and neutrophils wander
through the circulatory system using amoeboid motion
 As they wander, they engulf viruses and bacteria,
produce vacuoles to hold the viruses and bacteria, and
then fuse the vacuoles with a lysosome (a sac of
enzymes that kills bacteria).
 Cells called Natural Killer cells also wander around
and attack foreign cells by producing a toxin that
disintegrates the invader’s cell membrane and causes
the cell to lyse (These cells are not specific to their
targets)
B. Inflammation
 Injured cells release inflammatory chemicals such as
histamine (vasodilator, except in the lungs). This
creates heat and redness because of increased blood
flow
 Kinins are chemicals that are also released
and they activate pain receptors to cause pain and
swelling
 Chemotaxis then occurs which attracts phagocytes to
the area
Steps involved in inflammation:
1. Neutrophils enter the area and engulf pathogens and
cell debris
2. Monocytes follow and become macrophages within 812 hours (they engulf many more cells than
neutrophils)
3. Clotting proteins (fibrinogen and thromboplastin)
leak into the area and build a wall of fibrin around the
inflamed area so pathogens don’t spread
4. Sometimes the third line of defense comes into play (I’ll
talk about that later.)
5. Sometimes, macrophages don’t fully cleanse the area
and an abscess of pus is formed. This pus must be
drained before healing can occur. Pus = pathogens,
dead or dying neutrophils, and broken down tissues
C. Chemicals
 Complement – a group of 20 or more plasma proteins
that are activated when an antigen enters the body
a. complement attaches to the antigen when it
enters the body
b. complement forms holes in the invader
c. water leaks out of the invader and the cell lyses
d. this may initiate inflammation because
activation of complement causes release of
vasodilators and chemotaxis chemicals
 Interferon – (viruses must enter cells to do their work)
a protein produced by a viral infected cell to be released
and bind to nearby cell receptors to prevent infection
even further
 Fever – when macrophages attack invaders, they
release pyrogens in the process and this “turns up” the
body heat
a. excessive fever may denature enzymes
b. mild fevers denature bacterial enzymes, and
deprive them of iron because the liver gathers up
iron during a fever
c. fever speeds up cell repair activities
III.3rd line of defense: Developing immunity through the use of
antigens and antibodies
See Handout on Humoral (Antibody-mediated) immunity!
Proteins of the Immune System
Antibodies – (aka Immunoglobulins or Igs)
 Produced naturally in our bodies and are found on
the surface of B Cells (lymphocytes)
 Y shaped protein
 Each has a specific receptor site on it’s surface called
a combining site (concave shape)
 Each antibody has a complimentary antigen that fits
like a lock and key with the antibody
 Produced in response to only one antigen
Antigens – (Ag) Foreign substances such as proteins, pollen, bacteria
or viruses
 Usually found on the cell surfaces of invading cells
 Have a specific receptor site, called an epitope, that
fits with the antibody
 Self antigens are normally present in our bodies and
lymphocytes do not recognize these
 Foreign antigens are called non-self antigens
Major Histocompatability Complex (MHC) Collection of glycoproteins (protein and
carbohydrate) that exist on the membrane of all
body cells
 Only identical twins carry the same set of MHC
molecules
White Blood Cells of the Immune System
Lymphocytes –
B-lymphocytes – known as the antibody producers
 Lymphoid stem cells produce immature lymphocytes
(occurs before birth and is completed a few months
after birth)
 Immature B cells produce antibodies while still in the
bone marrow and insert these antibodies into their
cell membranes (genes determine this)
 Antibody bearing B cells enter the blood stream and
travel to the lymph nodes, spleen and liver
 They are now immunocompetent
T-lymphocytes – known as the cell mediators
 Lymphoid stem cells produce lymphocytes and send
them to the thymus gland
 In the thymus gland, T cells develop antibodies over
a period of 2-3 days, and display them on their cell
surface (These antibodies fit with only one type of
antigen)
 The cells are now immunocompetent, before they
even meet the antigen (genetic)
 T cells travel to the lymph nodes, liver, and spleen to
live and fight antigens
 T cells take on different roles
o Killer T cells (aka cytotoxic T cells) inject toxins
into the foreign cells and the cell ruptures
o Helper T cells produce interleukins
(communication chemicals between
leukocytes) to stimulate killer T cells and tell B
cells to divide and form antibodies
o Suppressor T cells suppress the helper T cells
and the killer T cells to prevent unnecessary
immune activity
Phagocytes - Neutrophils
Monocytes (which become macrophages)
(These are non-specific)