1.  Describe the 4 different types of hypersensitivity reactions and give an example of each. (8 points)

Hypersensitivity reactions are classified into four types:

i) Type I – Immediate hypersensitivity reactions

This is an allergic reaction induced by a specific antigen called an allergen usually provoked by reexposure to the same antigen and meditated by IgE antibodies. This result into an immediate local reaction called anaphylaxis.

Example: Anaphylaxis Atopic disorder
ii). Type II – Cytotoxic antibody reactions

In type II hypersensitivity, the antibodies produced during the immune response recognize and bind the antigens which form complexes that activate “classical pathway” generating mediators of acute inflammation at the site resulting to the creation of a membrane defect.

Example: autoimmune hemolytic anemia, Hemolytic disease of the new born.
iii). Type III – Immune complex reactions

In type II hypersensitivity, soluble immune complexes form in the circulation and deposit in various tissues and may trigger the classical pathway of complement activation. Mediators of acute inflammation are generated at the site of immune complex disposition.

Example: Serum sickness
iv). Type IV – Delayed hypersensitivity reaction

In type IV, helper T cells and CD8 cytotoxic cells are able to recognize extracellular and intracellular synthesized antigen when it is complexed with either class I or II MHC molecules.

Example: Hashimoto’s thyroiditis



2. Which cells are responsible for the release of histamine during a hypersensitivity reaction? (2 points)

They are the mast cells. The mast cells are scattered throughout the connective tissues of the body and store a number of different chemical mediators and upon stimulation by allergen, they release contents of their granules to surrounding places.




3. What does atopic mean in relation to patients with allergies? ( 2 points)

Atopic is a kind of allergy that is hereditary in nature and is characterized by an individual being able to produce high quantities of IgE histamines in response to allergens in the environment including cat dander, foods, pollen, dust, etc. The allergy becomes apparent only minutes after exposure.



4. What are the symptoms of a type 1 hypersensitivity reaction- name 4? Which two are of the most concern?(6 points)

1. Allergic rhinitis which is associated with hay fever

2. Allergic asthma

3. Atopic

4. Systematic anaphylaxis


The two of concern are;

1. Asthma that may induce a life threatening impaired breathing leading to anaphylactic shock.

2. Atopic


5. Describe desensitization therapy used to treat type 1 hypersensitivity reactions. ( 4 points)

Desensitization therapy refers to the treatment that is suggested to hypersensitive people. Desensitization therefore is a procedure that alters the immune response to a drug and results in temporary tolerance allowing the allergic patient to receive uninterrupted medication safely.  Desensitization for type I hypersensitivity reactions in penicillin allergic patients is usually recommended. Monoclonal antibodies (mAbs) are also important therapeutic tools with type I hypersensitivity. The mAbs target specific proteins and provide an efficient means of exploiting understanding of the disease mechanism to maximize therapeutic efficacy.


6. Describe the hypersensitivity reaction between a mother and her unborn fetus. (2 points)

This is an allergic reaction to the mother that stems from her unborn baby. It is a rare condition whereby the mother gets allergic to hormones that get produced in the growing baby, a condition called Polymorphic Eruption of Pregnancy.


7. What is Graves’ disease? (2 points)

Graves’ disease is an autoimmune disease in which a person’s own immune system attacks the thyroid gland and causing it to produce too much thyroxine causing the thyroid to expand twice its size and becomes more overactive leading to increased muscle weakness, heartbeat, and irritability.


8. What is alloimmunity? (2 points)

Alloimmunity is defined as the development of reactions to antigens that are produced by members of the same species as the body will recognize them as foreign and attack them as they would do if it were exposed to antigens from other organisms. Therefore, Alloimmunity is an immune response to antigens from members of the same species.


9. Why is type O blood referred to commonly as a “universal donor?” (2 points)

Blood group O is a universal donor because it lacks antigens and so when transferred to any other blood group, the antibody of the receiver will not react because blood group O has no antigens and hence there will be no clumping as result of the donated blood.


10. What happens when a patient receives the wrong blood type? (2 points)

If a patient receives the wrong blood type, then antibodies that the patient already has in his/her body will attack the donor blood’s red cells and destroy them resulting to allergic reactions, fever, back pain, chills, bleeding and may even result to death.


11. What type of antigens are present on type A blood? Type B blood? Type AB blood? Type O blood? (4 points)

Type A blood – antigen A

Type B blood – antigen B

Type AB blood – both A and B antigens

Type O blood – neither A or B antigen

12. What is the difference between primary and secondary immunodeficiencies? (2 points)

The differences between primary and secondary immunodeficiencies are basically based on the causes. Primary immunodeficiency is inherited (hereditary immunodeficiency) and therefore present at birth while secondary immunodeficiency is acquired or triggered after birth and therefore it is due to an underlying condition.


13. What cells do the HIV virus infect? (2 points)

The helper T cells


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