This document discusses different types of hypersensitivity reactions: Type I reactions are immediate allergic reactions mediated by IgE antibodies that cause mast cell and basophil degranulation within minutes. Common examples are allergies. Type II reactions involve cytotoxic antibodies binding to antigens on cell surfaces and tissues, leading to immune-mediated destruction of cells. Examples include hemolytic anemia and drug reactions. Type III reactions are immune complex-mediated and occur 2-6 hours after antigen exposure, examples being serum sickness and systemic lupus. Type IV delayed hypersensitivity reactions cause inflammation within 2-6 hours, peaking at 24-48 hours, with examples including poison ivy and chronic asthma.

1. HYPERSENSITIVITY
By,
Rajamehala M

3. What makes us sick?
“enemies” in the environment in the form of microbes and chemicals are
constantly attacking our bodies, disrupting homeostasis
sometimes immune system homeostasis is disrupted on its own
2
it may over-react to
antigens such as
with allergies
it may under-react as
with human
immunodeficiency
virus infection (HIV)
it may react to self
proteins as with
autoimmune disease

5. Hypersensitivity reaction
The immune system is an integral part of human protection against
disease, but the normally protective immune mechanisms can
sometimes cause detrimental reactions in the host.
Any immune response against a foreign antigen exaggerated beyond the
norm
Such reactions are known as hypersensitivity reactions, and the
study of these is termed immunopathology.

6. Gell & Coombs Classification
Type I:Immediate hypersensitivity
onset within minutes of antigen challenge
examples are allergies to molds, insect bites
Type II: Cytotoxic hypersensitivity
onset within minutes or a few hours of antigen challenge
examples are adult hemolytic anemia and drug allergies
Type III: Immune complex-mediated hypersensitivity
onset usually within 2-6 hours
examples include serum sickness and systemic lupus
Type IV: Delayed Hypersensitivity
inflammation by 2-6 hours; peaks by 24-48 hours
examples include poison ivy and chronic asthma

7. Type I (Anaphylactic) Reactions
Occur within minutes of exposure to antigen.
Antigens combine with IgE antibodies
IgE binds to mast cells and basophils, causing them to undergo
degranulation and release several mediators:
❖ Histamine:Dilates and increases permeability of blood vessels
(swelling and redness), increases mucus secretion (runny nose),
smooth muscle contraction (bronchi).
❖ Prostaglandins: Contraction of smooth muscle of respiratory
system and increased mucus secretion.
❖ Leukotrienes:Bronchial spasms.
Anaphylactic shock: Massive drop in blood pressure. Can be
fatal in minutes.

8. Biological basis of allergies
histamine

9. Type I hypersensitivity – sensitization to an inhaled allergen or bee sting
Antigens (red dots) from inhaled pollen are ingested and presented by
macrophages to T cells. Activated T cells produce cytokines leading to
the production of IgE, which binds to receptors on mast cells and causes
the release of histamine, which is responsible for allergy symptoms.
Onset is usually within minutes of contact with antigen.
Mast
cell
cytokines
→ →

10. Sensitization

15. •https://www.youtube.com/watch?v=uW96-mBFGag

16. Type II. Cytotoxic Type
Body makes special autoantibodies directed against self-cells
(antigens present on the surface of cells or other tissue
components)
antigen:
may be intrinsic to the cell membrane
may take the form of an exogenous antigen adsorbed on the
cell surface.
hypersensitivity results from the binding of antibodies to normal
or altered cell-surface antigens

22. Type II hypersensitivity – immune-mediated
destruction of red blood cells
Drug (p=penicillin) modified red blood
cells induce the production of
antibodies, because the bound drug
makes them look foreign to the immune
system. When these antibodies are
bound to them, the red blood cells are
more susceptible to lysis or
phagocytosis.
Onset is dependent on the presence of
specific antibodies.

24. Type II examples
1. Transfusion reactions
✔ cells from an incompatible donor react with the host’s antibody
2. Erythroblastosis fetalis
✔ there is an antigenic difference between the mother& the fetus, and
antibodies (IgG) cross the placenta & cause destruction of fetal red
cells.
3. Autoimmune hemolytic anemia, agranulocytosis, throbocytopenia
✔ individuals produce antibodies to their own blood cells, which are
then destroyed.
4. Drug reactions
✔ antibodies are produced that react with the drug.

26. https://www.youtube.com/watch?v=xllsDG2PXIk

27. Hypersensitivity Reactions