Biology 2108
Lecture
Physiology:
Immune System
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A very powerful set
of weapons that hence require very sophisticated,
complex
regulation.
Three
lines of defense:
First Line of
Defense - External Defenses of the Innate Immunity:
Barriers
preventing disease-causing organisms (DCO) from entering the body
What
is the most obvious barrier and why is this insufficient?
Secretion such as sweat also have low pH and contain the enzyme
lysozyme.
What aspects of the digestive and respiratory systems might serve as a
first line of defense?
The pH of the female reproductive tract is also slightly
acidic.
How do sperm survive
there?
Second Line of
Defense- Internal Defenses
of the Innate Immunity: Responses to cells that are not
recognized as self
Examples:
Histamine release and temperature response. Are runny noses and fever, in themselves, a bad thing?
Phagocytes (leukocytes
including neutrophils, monocytes, and
eosinophils) destroy foriegn cells in
various ways including engulfing and by secreting lysosomal enzymes.
Leukocytes in general must be able to distinguish cells of the body
(self) from cells of disease-causing organisms. Why?
Immune cells repond to any cells WITHOUT the set of surface proteins
(major histocompatibility markers) on the
cell
membrane unique to all cells of the body in each individual.
i.e. These proteins
mark cells of the body as SELF,
analogous
to a military uniform used to identify one's own countryman.
There are over 100 different forms (alleles) of MHC in the human
population.
Why is it
likely that a transplanted tissue is will be rejected unless the donor
and recipient are closely related?
What would be a
more effective weapon: one that is designed to combat anything that is
recognized as foreign, or one that is designed to combat a specific
invading threat?
Third
Line of Defense- Acquired Immunity: Specific responses to specific threats
Lymphocytes (another type of
leukocyte) - B cells and
T cells
What to understand about the
diagram above:
- A specific antigen (the
macromolecule, typically part of the DCO, that elicits an immune
response) can only activate specific B
and T cells. Of millions of B and T
cells types produced by the body, one type
that
is specific for destroying a particular type of disease causing
organism is rapidly produced in the presence of that
specific antigen of the DCO. The race is on.
- The antigen must be exposed to a helper
T cell before the
specific type of B cell or cytotoxic T cell (both of which must also be
exposed to the antigen) can begin to multiple rapidly (i.e.
is stimulated). This provides a 'check' prior to initiating a
major immune response. What
cell type is critical in this response and what disease disables this
cell type?
- There are two general responses: antibody-mediated
B cell response and cell-mediated
T cell response (see descriptions at bottom of the above
diagram).
- Memory cells are produced
that are specific to that antigen and result in a much faster response
to the disease in the event of future infections (i.e. immunity to that disease is
conferred). Why faster?
What if only the antigen of a
disease-causing organism were presented to the immune system?
When Europeans colonized the
America's, European diseases devastated Native American populations,
but few if any major diseases crossed the Altantic in the opposite
directions. Why was the transfer of
diseases so one-sided?
The Big
Picture: The body
must use immune
weapons carefully, balancing power with caution.
Ability to
recognize
abnormal cells:
if poor,
then
-slow response to disease-causing organisms
-cancer (the
bodies own cells dividing out of control)
if too efficient,
then
-allergies (immune
response to non-dangerous substance) Why
are allergies more common in developed
nations?
-autoimmune diseases
(the
immune system attacks cells of the body)
-reproductive failures
(sperm
and fetal tissue can be recognized by the immune system as non-self; Why? How is rejection prevented?)
