Allergic responses are abnormal immune reactions to substances that are harmless to most people. There are four main types of allergic responses: 1. Type I reactions are IgE-mediated and involve mast cell degranulation, causing symptoms like asthma. 2. Type II reactions are antibody-mediated and cytotoxic, destroying cells through complement activation or antibody-dependent cellular cytotoxicity. 3. Type III reactions involve immune complex formation, activating the complement system and causing inflammation. 4. Type IV reactions are T cell-mediated, where sensitized T cells secrete cytokines triggering delayed inflammatory responses.

1. Allergic Responses
Presented by: Kiran Hanif

2. Allergic Responses
 Also called Hypersensitive responses
 Hypersensitive immune reaction to a substance harmless for
healthy individuals.
 A type of abnormal immune reaction
 Substances induces abnormal immune responses are called
Allergen.

3. Atopy
 A genetic trait to have a predisposition for localized
anaphylaxis.
 Atopic individuals have higher levels of IgE and
eosinophils.

4. Genetic Predisposition
 Candidate polymorphic genes include:
 IL-4 Receptor
 IL-4 cytokine (promoter region)
 FceRI
 Class II MHC (present peptides promoting Th2 response)

5. Types of Allergic Reactions
1. Type I or IgE-mediated Hypersensitivity
2. Type II or IgG or IgM-mediated cytotoxic
Hypersensitivity
3. Type III or Complex-mediated Hypersensitivity
4. Type IV or Cell-Mediated Hypersensitivity

6. Type I or IgE-mediated Hypersensitivity
 Commonly called Allergy
 Allergen presented by antigen presenting cells
 TH2 cells activate the B cells
 B cells give clonal cells
 Plasma cells
 Memory cells

7. Cont……
 Plasma cells secreted IgE antibody
 Secreted IgE bind to the Fc Receptors
 Receptors present on Mast cells & Basophills
 Degranulation is induced
 Mediators (Histamine) releases
 Results in clinical manifestations

8. General mechanism showing type I hypersensitivity reaction

9. Allergens
 Nonparasitic antigens responses capable of
stimulating type I hypersensitivity
 Stimulate inappropriate IgE production
 Binds to IgE and induces degranulation of cells

10. Proteins
• Foreign serum
• Vaccines
Plant pollens
• Rye grass
• Ragweed
• Timothy grass
• Birch trees
Drugs
• Penicillin
• Sulfonamides
• Local anesthetics
• Salicylates

11. Foods
• Milk
• Sea Food
• Nuts
Insect products
• Bee venome
• Wasp venom
• Drugs Ant venom
• Cockroach calyx
• Dust mites
Animal hair and dander

12. Fc Receptors
 Receptors present on the surface of the Mast cells
and Basophills
 Two types of Fc receptors are found
 High affinity receptor (FcɛRI)
 Low-affinity receptor (FcɛRII)
 Binding of IgE to receptors induces degranulation

13. Structure of high affinity receptor FcɛRI

14. Structure of low affinity receptor FcɛRII

15. Biochemical events in mast-cell activation and degranulation

16. Mediators releases after Degranulation
of Mast cells
 Mediators are the molecules mediate clinical
menifestations
 Pharmacologically active agents act on local tissues
 Mediators release induced by allergens results in:
 Increase in Vascular permeability
 Inflamation

17. Classification of Mediators
 Classified as:
 Primary mediators
 Secondary mediators

18. Primary Mediators
Histamine
 Constriction of smooth muscles.
Bronchiole constriction = wheezing.
Constriction of intestine = cramps-diarrhea.
 Vasodilation with increased fluid into tissues causing
increased swelling or fluid in mucosa.
 Activates enzymes for tissue breakdown

19. Secondary Mediators
Leukotrienes
Prostaglandins
Cytokines

20. Effect of mediators

21. Phases of type I Hypersensivity reactions
Immediate phase
 Involves LTC4 and PGD2
Late phase
 Involves IL-4, IL-5, ECF, PAF

22. Type I reactions
 Type I reactions may be systemic or localized
 Systemic anaphylaxis
 Localized hypersensitivity reactions
 Allergic rhinitis
 Food allergies
 Asthma

23. Asthma
 Triggering of disease involve exposure to airborne
& blood-borne allergens such as pollens, dust,
fumes, insects products etc.
 Asthematic response can also be divided into:
 Early response
 Late response

24. Early and late responses in asthema

25. Effect of degranulation of mast cells in asthema

26. Regulation of Type I response
 Many factors are responsible for regulating the type
I response which include:
 IL-4
 IL-5
 IL-9
 IL-13

27. Medical control of Hypersensitivity
 Antihistamines
 Cromolyn sodium
 Theophylline
 Epinephrine

29. Type II or IgG or IgM-mediated
cytotoxic Hypersensitivity
 Also called Antibody-mediated cytotoxic
hypersensitivity
 Involve antibody-mediated destruction of cells
 Antibody bound to a cell surface antigen can
activate complement system
 Cell destruction by ADCC

30. Type II Reactions
Transfusion reactions
Drug-induced Hemolytic Anemia
Hemolytic disease of Newborn

31. Hemolytic disease of the newborn
 Also called Erythroblastosis fetalis
 Develops when maternal IgG antibodies specific for
fetal blood- group antigens cross the placenta
 Destroy fetal red blood cells
 Commonly develops when an Rh+ fetus expresses
an Rh antigen on its blood cells

32. Type III or Complex-mediated
Hypersensitivity
 Reaction of antibody with antigen generates
immune complexes
 Complexing facilitates the clearance of antigen by
phagocytic cells.

33. Effector mechanism
 Immune complexes activate the complement system
 Anaphylatoxins C3a, C4a, and C5a cause localized
mast-cell degranulation.
 C3a, C5a, and C5b67 are also chemotactic factors
for neutrophils
 Release of lytic enzymes by neutrophils

34. Development of localized type III hypersensitivity

35. Type III reactions
Poststreptococcal glomerulonephritis
Rheumatoid arthritis

36. Type IV or T Cell-Mediated
Hypersensitivity
TH cells encounter certain types of antigens
Secrete cytokines induces localized inflammatory
reaction
Reactions are delayed by one or more days

37. Phases of DTH response
Sensitization phase
 begins with an initial contact with an antigen.
Effector phase
 subsequent exposure to the antigen
 TH1 cells secrete a variety of cytokines
 Activate the macrophages

38. Phases of type IV hypersensitivity

39. Contact dermatitis is type of DTH
response
Molecules complex with skin proteins
Complex internalized by skin cells
Processed & presented with MHC II
Results in activation of sensitized TH1 cells

40. Development of DTH response after second exposure to
poison oak

41. Four types of Allergic responses