This document provides an overview of hypersensitivity reactions. It discusses the classification of hypersensitivity into four main types based on the mechanism of pathogenesis: Type I mediated by IgE antibodies, Type II mediated by IgG antibodies, Type III involving immune complexes, and Type IV mediated by T-cells or delayed hypersensitivity. Key features of each type are outlined, including examples like allergic reactions, autoimmune diseases, serum sickness, and contact dermatitis. The roles of antibodies, antigens, T-cells, and macrophages in different hypersensitivity pathways are also summarized.

1. Presented by
MARIYA RAJU

2. HYPERSENSITIVITY

3. The term allergy is coined by VON PIRQUET
Clemens von Pirquet

4. Inducing Antigens are called ALLERGENS

5. Classification of Hypersensitivity
Reactions
I. Based on Time
1.Immediate type Hypersensitivity Reactions
2.Delay type Hypersensitivity Reactions

6. DIFFERENCE BETWEEN IMMEDIATE
AND DELAYED HYPERSENSITIVITY
Immediate type
Hypersensitivity Reactions
Delay type
Hypersensitivity Reactions
 It appears and disappears
rapidly.
 It appears slowly &last longer.
 It is induced by the intake of
antigen by any route.
 Only by skin contact
 It is antibody mediated B-cell
response.
 It is T-cell mediated response.
 Desensitisation easily but
short living.
 It is difficult but long living.

7. II Gel and Coomb’s classification:
(Based on mechanism of Pathogenesis)
a) Type I Hypersensitivity Reactions( Ig E mediated
Hypersensitivity Reactions)
b)Type II Hypersensitivity Reactions(Ab mediated
Hypersensitivity Reactions)
c)Type III Hypersensitivity Reactions(Ag-Ab mediated
Hypersensitivity Reactions)
d)Type IV Hypersensitivity Reactions(cell-mediated
Hypersensitivity Reactions or Delayed type Hypersensitivity
Reactions)

8. TYPE I- ANAPYLATIC REACTION
 IgE mediated hypersensitivity reaction
 The term ANAPHYLAXIS means ,
Ana- against
Phylaxis – protection
 Systemic anaphylaxis is a rare event in man but occasionally
observed in hypersensitive individuals by insect stings

9. MECHANISM

11. CHEMICAL MEDIATORS
MEDIATORS SOURCE BIOLOGICAL
EFFECTS
PRIMARY
MEDIATORS
1)Histamine Mast cells basophils Formed by
decarboxylation of
histidine, present
in granules of mast
cells,basophils
2)Eosinophilic
chemotatic factor of
anaphylaxis(ECF-A)
Mast cell granules Eosinophil
chemotaxis
SECONDARY
MEDIATORS
1)Prostaglandins and
thromboxanes
Distributed in
tissues, released
during anaphylaxis
Derived from
arachionic acid
2)Platelet activating
factor(PAF)
Mast cells ,
monocytes
Aggregation of
mast cells
Neutrophil
chemotaxis

12. FEATURES OF ANAPHYLAXIS
 Reaction occurs immediately within few seconds to minutes
 Symptoms results from constriction of smooth muscles
 Short duration
 Slight cellular damages
 Not a heritable diseases

13. 1)SYSTEMIC ANAPHYLAXIS
 Rarely occurs in man
 It includes active anaphylaxis,passive anaphylaxis,cutaneous
anaphylaxis
 It is a shock condition, which usually follows administration of
horse serum like ATS,ADS
 Lung is the principle shock organ in humans
 Liver is the target organ in dog

14. LOCALIZED ANAPHYLAXIS
 Two types
1)MUCOSAL ANAPHYLAXIS:Application of small dose of
antigen on mucosal surface like conjunctive , respiratory tract
leads to Rginorrhoea, Bronchospasm respectively
2)CUTANEOUS ANAPHYLAXIS:It is induced both by
cutaneous injection of antigen

15. Bronchospasm

16. Rginorrhoea

17. CUTANEOUS ANAPHYLAXIS

18. ATOPY
 Type I hypersensitivity reaction that occurs spontaneously in response
to substance encountered in the environment in everyday life
FEATURES
 Reaction occurs at the site of entry of the exciting
 Routes of entry:Inhalation of pollens affect lungs
 It is IgE mediated hypersensitivity
 Eg :Hay fever – air borne disease,infection in conjunctiva and nasal
mucosa, sneezing, Respiratory tract irritation
 Atopic Dermatitis – Inflammatory disease in skin .mainly occur in
children’s
 Asthma – Allergic asthma and intrinsic asthma are air born diseases

19. Hay fever

20. Atopic Dermatitis

22. TESTS FOR ANAPHYLAXIS
1) SKIN TEST
 Amount of 0.1 ml of diluted serum or antigen is injected
intradermally on forearm, flare appears in a few minutes
in positive reaction
2)CONJUNCTIVAL TEST
 One drop diluted antigen when placed in conjunctival sac of
one eye , redness of the eye with itching

23. SKIN TEST

24. CONJUNCTIVAL TEST

25. ANAPHYLACTOID REACTION

26. Type II Hypersensitivity Reactions
(Ab mediated: CYTOTOXIC AND CYTOLYTIC)
 These reaction involve a combination of IgG antibody with the
the antigenic determinants on the surface of cells leads to
cytotoxic or cytolytic effects
 Eg:Lysis of red cells by antierythrocyte antibody in
autoimmune anemias and hemolytic disease of the newborn
 Mainly Ig G mediated Response

27.  2 types of mechanisms
a) Complement mediated lysis (Opsonisation)
b) Cytotoxic action of NK cells and Neutrophil (ADCC-
Antibody dependent cell mediated cytotoxicity)
 If Ag size is smaller, opsonisation and if the size is longer
ADCC mechanism
 When the phagocytic cell is unable to phagocytise the longer
particle release lysosome which may induce cell damage

29. Eg: for Type II Reactions
1. Drug Induced Reactions
Drugs like Pencillin, Streptomycin, etc may bound on the surface of
erythrocyte leads into the formation of hapten-carrier complex which induce
complement activation and cause complement mediated lysis

30. 2.ABO Blood group reactions

31. 3.Auto Immune Diseases

32. 4.ErythroblastosisFoetalis

33. TYPE III(IMMUNE COMPLEX REACTION)
Ag-Ab mediated
 It is a type of humoral antibody mediated hypersensitivity
 It is characterized by deposition of Ag-Ab complexes in
tissues,that leads to tissue damage

34. PRINCIPLE

35. 1) ARTHUS REACTION
 Discovered by Arthus in 1903
Nicolas Maurice Arthus

36. CONT….
 It is a localized infection occurs after 2-8 hours after infection
 Very high level of Ig G in serum and high concentration of Ag in
tissue space
 Symptoms: Tissue necrosis, Oedema, Hemorrhage, etc..

38. Eg : Arthus Reactions
a) Farmer’s Lung disease

39. b)Pigeon Fanciers Disease

40. 2.Serum Sickness

41. TYPE IV REACTIONS:
DELAYED HYPERSENSITIVITY
 Occurs after 72 hours
 Ab has no role
 This is due to the action of sensitised T-cell mechanism
 When an Ag is exposed to a sensitised T-cell,it produce proteins like
lymphokinins
 These proteins activate Macrophage
 Activated Macrophages release lytic enzyme which induce tissue damage

43.  TWO TYPES OF DELAYED HYPERSENSITIVITY
ARE RECOGNISED
1) TUBERCULIN(INFECTION ) TYPE
2) CONTACT DERMATITIS

44. 1)TUBERCULIN(INFECTION ) TYPE

45. tuberculin Protein is injected
responses may occur with in 30-
48 hours

46. 2) Contact dermatitis

47. Overview of the DTH response.

49. HYPERSENSITIVITY REACTIONS OVERVIEW