Download Self and Non Self The Underlying Principle of the Immune System

Self and Non Self
The Underlying Principle of the Immune System
Model 1
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4
5
There are twenty three (23) chromosomes in an egg cell, and 23 chromosomes in a sperm cell.
After fertilization, the resulting cell (the “zygote”), has 46 chromosomes. The zygote divides
into two cells, then those two cells divide to form four cells, then those four cells divide to form
eight, and so on.
Questions:
Question 1. In the above image, how many sperm are initially surrounding the egg? How many
eggs are present? Did every sperm “fertilize” the egg?
One egg and eight sperm. Only one egg fertilized the egg
Question 2. What happened to the other sperm?
The other sperm failed; they died without fertilizing an egg.
Question 3. What are “monozygotic twins?” Can all the cells in both individuals be linked to
one zygote?
Monozygotic twins originate from one zygote. Both individuals come from one zygote.
Is it possible to have monozygotic triplets?
Yes – all three individuals will come from one zygote.
Along with monozygotic twins, what other types of twins exist? In the space below, write one
sentence to explain how they are formed.
Two eggs and two sperm “fraternal” twins – or di-zygotic twins. Twins that result from
multiple fertilization.
Question 4. After the reader has read the following question, think about possible answers on
an individual basis for about 30 seconds, and then discuss your ideas with the group. Your
group should be able to derive the correct answer.
Humans are susceptible to having Streptococcus bacteria (commonly called “strep”) residing in
their respiratory systems. Can these bacteria be linked back to the human zygote? (Do they
originate from a human zygote?)
No – they do not originate from the human zygote. They are “outside” that cell line.
Question 5. Almost all humans have bacteria, specifically Escherichia coli (or E. coli), within
their large intestines. Can these bacteria be linked back to the individual’s zygote?
No – they do not originate from the human zygote. They are “outside” that cell line.
Given your answers in questions 4 and 5, as a group, revise your answer to question 2 above.
Question 6. It is estimated that an adult body is comprised of 50 trillion cells. Can all these cells
be linked back to the one original zygote?
Yes
Note – students may return to this question and then possibly change their answer to
“No” but students should also question “are bacteria a part of us? Or are they separate
from us?” Which leads to questions about types of relationships with other organisms –
commensalism, etc. Generally, bacteria that are on the body surfaces, or within the
lumen of our intestines, or in our respiratory tracts, are NOT considered a part of our
body. The latest information has the number at 100 trillion.
Question 7. After an egg is fertilized by a single sperm a number of scenarios can occur:
a. The fertilized egg develops into a zygote, then an embryo, then a fetus, and finally a
baby is born.
b. The fertilized egg can divide right after fertilization (zygote stage) and form twins.
c. The fertilized egg can divide later in the development of the zygote also forming
twins.
Would the time of the fertilized egg division impact how “identical” the twins would be in
scenarios b and c?
Not from a genetic standpoint, they would have the same DNA and be as identical as the
twins that resulted from the fertilized egg dividing shortly after fertilization.
There could however be issues with the developing fetuses resulting in co-joined twins.
Model 2:
When kidney transplants were beginning in the 1950s, “tissue rejection” often occurred and
death was quick. Then, by chance, a monozygotic twin who was suffering kidney failure
received a donor kidney from his twin, who had two healthy kidneys. Tissue rejection did not
ensue and both individuals went on to live for many more years.
Question 8. Between the two monozygotic twins there were a total of four kidneys. Can all
four kidneys be linked to one zygote?
Yes
Question 9. Think about the following question individually for 1 minute, then discuss your
ideas with your group for about 2 minutes, and finally have the “recorder” write one response
for the entire group.
What is “tissue rejection?” How does the body “reject” an organ?
Tissue rejection is when the immune system attacks, kills, or neutralizes a transplanted
organ due to being identified as “non-self.” Advanced students might mention autoimmune disease – when tissue from the zygote (self tissue) is mistakenly is identified as
non self tissue.
Question 10. Would the twin receiving the kidney from his identical twin need to take any
immune suppressing medication?
No, because the kidney is an identical match. Immune suppression medication is given
to prevent a person from rejecting a foreign tissue that has been put into their body.
Question 11. A key concept in tissue transplants is the notion of “self” vs. “non-self.” Using the
information above, what is the difference between “self” and “non-self” items?
Self-tissue comes from the same zygote. Non self-tissue comes from a different source
(not the zygote) Note: bacteria do not come from a zygote … so “a different source” is a
more accurate response. Bacteria typically come from “the environment” – e.g.,
interacting with an infected individual.
Question 12. Why do you think tissue rejection did not occur in the above case involving
monozygotic twins?
Because it is “self” tissue – it comes from the same zygote.
Question 13. Using your knowledge of the immune system identify the following items as “self”
or “non self”
Organ / Item
Your heart
Self or NonSelf
Self
Your brain
Self
A transplanted
heart from a
distant relative
A kidney from a
monozygotic twin
Non - Self
Self
Organ / Item
Self or Non-Self
Blood from a blood
Most likely nonbank (unknown donor)
self
Artificial knee made of
titanium.
Non - Self
E. coli found in the
lumen of the large
intestine
Transplanted heart
valve that originated
in a pig.
Non - Self
Non - Self
Question 14. Using the concept of “self and non-self,” what is the function of the immune
system?
The function of the immune system is to identify non-self items and destroy / kill /
neutralize non-self-items. Note: answers will vary
Question 15. The following question is quite difficult, and may require drawing a “pedigree” (a
chart showing father, mother, kids, etc.). After the reader has read the question, work on an
individual basis for 2 minutes to try to derive the correct answer, and then discuss your ideas
with the group. The recorder should write down one answer for the entire group.
(Hint: There is a correct answer, and that answer has one key word. Does anyone in the group
know the one key word?)
Two monozygotic males mate with two monozygotic females. Each pairing produces two more
sets (four total individuals) of identical twins (all boys). Are all four boys identical to each
other? Could all four share kidneys if necessary? Explain.
All four boys are NOT identical. The two individuals within each set are identical to each
other (each set of monozygotic twins) but there are differences between the two sets.
What is the one key word that provides the foundation to the correct answer?
The key word is MEIOSIS
Other words: independent assortment, crossing over
Question 16. The placenta provides the boundary that separates a fetus from the mother’s
immune system. Both the mother and developing fetus are involved in the suppression of her
immune system, ensuring survival of the fetus. There are however situations where the mother
can abort a fetus because of immune intolerance.
Take 1 minute to think of what situations could cause a mother to abort a fetus due to immune
intolerance and then confer with the other members of your group to generate a list of
scenarios.
Hemolytic disease of the newborn or Rh+ intolerance: mother rh(-), fetus/newborn Rh(+).
During all pregnancies a small amount of fetal blood can mix with the mother’s blood.
There is no noticeable problem during the first pregnancy although she would be making
antibodies to the Rh(+) antigen. In subsequent pregnancies where future fetuses are
also Rh(+) the mother will attempt to abort the fetus or at the very least the fetus or
newborn would need a blood transfusion. Note: Since 1968 rh(-) mothers have generally
been given Rh immune globulin, which will prevent the mother from producing Rh(+)
antibodies.