LECTURE OUTLINE #1: Defense Mechanisms and the Immune System
I.
INTRODUCTION
Living
organisms are masses of organic matter that are under constant attack by
microorganisms.
We are only
aware of the phenomena that are detected by our sensory nervous system.
II. NON-SPECIFIC DEFENSE MECHANISMS
1.
First line of defense:
a. the
skin: collagen, sweat
glands, and lysozyme (for
pronunciation, click lysozyme).
b. mucose membranes: mucus secretions, nostril hairs, and ciliated epithelial
cells.
2.
Second line of defense:
a.
phagocytic white cells: neutrophils, monocytes, eosinophils, and natural killer cells.
b.
antimicrobial proteins: lysozyme, interferons (interferon),
and complement system.
c.
inflammatory responses: hyperemia (hyperemia)
and increase in blood flow.
III. THE
IMMUNE SYSTEM: SOME BASIC CONCEPTS
1. antigens
(antigen) are any foreign substances that elicit an immune
response:
a. they
include molecules of viruses, bacteria, fungi, protozoans,
and parasitic worms.
b. they
include surface molecules on pollen, insect venom, and transplanted
tissues.
2. antibodies
(antibody) are large proteins (IGs) produced by lymphocytes to
counter antigens (Fig. #1)
3. development of immunocompetence
of B-lymphocytes
and T-lymphocytes.
4. humoral immunity: the role of B-lymphocytes.
5. cell-mediated
immunity: the role of
T-lymphocytes.
IV.
EXAMPLE OF A TYPICAL (albeit complex) IMMUNE RESPONSE (Fig.
#2)
(NOTE: An immune response is any reaction of the immune system.)
1. Although
it is a basic humoral
response, it requires macrophages
and T cells, plus B cells.
2. First, a
macrophage phagocytozes
a virus and the viral antigens on its
surface.
3. The partially digested antigens are displayed
in association with class II MHC molecules
imbedded in plasma
membrane of a macrophage
(now called an antigen-presenting cell).
4. A T-helper cell recognizes
this self/non-self complex on the macrophage and binds to it.
5. This contact
stimulates the T-helper cell to form clones of T cells keyed to the
specific antigen.
6. At the same time, a limited number of B cells also become attached to
the virus, and incorporate the viral antigen into their cytoplasm.
7. the cloned
T cells actively seek out the B cells that display the same viral antigen.
8. When the T cells form a complex with the B
cells, they begin producing cytokines
(cytokine), a family of biochemicals that promote cell division,
or mitosis.
9. This stimulation of the B cells by cytokines causes
them to rapidly divide (clone) and develop into many plasma cells that
manufacture and secrete antibodies
against the original virus.
10. The plasma cells can secrete as many as 2000
antibody molecules per second for their 4-5 days of existence, i.e., as
many as 864,000,000 in a life-time.