Concepts of hypersensivity should be well versed to all medical personnel to understand its implications. I have made it very simple to all readers to understand the same

1. Type 1 hypersensitivity reaction
(allergy)
Dr. Prathyusha
PG in ENT Narayana Medical College
NELLORE

2. once upon a time………
• Menes, the first
Egyptian pharaoh ruled
about 3100 BC.
• The plate of his empty
tomb appears to show a
wasp or hornet
• suggest that Menes died
from a wasp sting ?.

3. 100 yrs ago…..
• An young paediatrician understood that the function of the immune
system should be rationalized
• NOT in terms of exemption of disease
• but in terms of change of reactivity.
• He coined a new word to represent such an idea….ALLERGY
(“unfortunately used as a slang in our day today life”)
• In his own words….
• “the first contact of the immune system with
an antigen changes the reactivity of the
individual on the second and subsequent
contacts, this change (or allergy) can induce a

4. • Clemens Peter von Pirquet
(May 12, 1874 – February 28, 1929)
• Austrian scientist and pediatrician
• Patients who were injected with horse serum or
smallpox vaccine had quicker, severe reactions
to second injections.
• The collection of symptoms resulting from
serum injections, he gave the name serum

5. He is none other than ….
Pirquet during those
days……

6. Meanwhile…..
• Two French scientists, Paul Portier and Charles Richet,
investigated the violent stings of jellyfish.
• concluded that the reaction was the result of toxins.
• Used isolated jellyfish toxins as vaccines and injected to
dogs.
• with subsequent booster doses dogs had asphyxia and
vomiting and diarrheas
• This overreaction was termed as anaphylaxis by them
• Anaphylaxis (opposite to prophylaxis )
• Richet was subsequently awarded the Nobel Prize in

10. First of all hypersensitivity
• Exaggerated or misdirected immune response
• Results in tissue injury or other pathophysiological
changes
• Occurs when an already sensitized individual is re-exposed
to the same foreign substance
• May be immediate or delayed

11. Gell and Coomb classification

12. Components of type 1
hypersensitivity
• Antigens
• Antibody IgE (Reagenic antibody)
• Antigen presenting cells
• Basophil
• Mast cell
• Eosinophil
• Helper 2 Th2Cells
• B cells
• Inflammatory molecules

13. Antigens

16. Characteristics of an antigen
• Small 15-40,000 MW proteins.
• Specific protein components
• Often enzymes.
• Low dose of allergen
• Mucosal exposure.
• Most allergens promote a Th2 immune response

17. Prior Sensitization
required…………..
• the allergen stimulates the production of allergen-
specific IgE antibodies by
plasma cells in susceptible individuals.
• The allergen-specific IgE attaches itself to the surface of
mast cells in various
tissues and basophils in the blood in a process known
as sensitization.

18. Macrophage and exposure of an
antigen• Antigen-presenting cells fall into two categories:
• professional
• non-professional.
• Those that express MHC class II molecules
Co-stimulatory molecules
Pattern recognition receptors are
• The non-professional APCs express MHC class I molecules.
Professional A

21. Activation of T helper cell
• T cells cannot recognize and DO NOT respond to, 'free' or
soluble antigen.
• The APC involved in activating T cells is usually a
macrophage
• the T cells recognize and respond to antigen that has been
processed and
presented by cells via carrier molecules like MHC
molecules.

24. Activated T cell
• Stimulate B cells and their proliferation to plasma
cells
• Stimulates other T helper cells

28. Isotype switching of plasma cell

30. Isotype switching requires
• B cell class switch to IgE requires T cell help:
• CD40L and IL-4 or IL-13 (Th2 cytokines)
• The propensity to make an IgE response to
• environmental antigens varies among individuals

31. After Ig E production
• IgE produced by plasma cells is rapidly taken up
• by FcεRI
• Tissue mast cells and
• Circulating basophils
• (serum τ½~2 days; compare to IgG~21 days)

33. IgE receptor
• The high-affinity IgE receptor, also known as FcεRI,
• FcεRI is a tetrameric receptor complex consisting of
• one alpha (FcεRIα - antibody binding site),
• one beta (FcεRIβ - which amplifies the downstream signal),
• and two gamma chains (FcεRIγ - the site where the
downstream signal initiates) connected by two disulfide
bridges.

35. Secondary exposure to allergen
• Mast cells are primed with IgE on surface.
• Allergen binds IgE and cross-links to activate
• signal with tyrosine phosphorylation,
• Ca++ influx,
• degranulation
• release of mediators

40. • Secondary mediators
• Mediators formed after activation
• Leukotrienes
• Prostaglandins
• Th2 cytokines- IL-4, IL-5, IL-13, GM-CSF

41. LOCAL ANAPHYLAXIS
• Two phases:
• Initial response
• Vasodilation, vascular leakage, smooth
muscle spasm or glandular secretions
• 5-30 min. after exposure
• subside in 60 minutes

42. • Late-phase reaction
• 2-8 hrs. later without additional exposure to
antigen
• More intense infiltration of tissues with
• eosinophils,
• neutrophils,
• Basophils,
• monocytes &
• CD4+ T cells

43. SYSTEMIC ANAPHYLAXIS
• Occur after administration of
• heterologous proteins (e.g. antisera),
• hormones,
• enzymes,
• polysaccharides & drugs
• itching, hives & skin erythema
• contraction of resp. bronchioles + resp. distress
laryngeal edema

45. • Continuation of sensitization cycle
• Mast cells control the immediate response.
• Eosinophils and neutrophils drive late or chronic
response.
• More IgE production further driven by
• Activated Mast cells, Basophils, Eosinophils.

46. Role of eosinophils
• Continuation of sensitization cycle
• Eosinophils
• Eosinophils play key role in late phase reaction.
• Eosinophils make – enzymes,
• cytokines (IL-3, IL-5, GM-CSF),
• Lipid mediators (LTC4, LTD4, PAF)
• Eosinophils can provide CD40L and IL-4 for B cell
activation.

48. To summarize……………..

50. Atopy
• Preponderance of certain individuals for
allergies

51. genetic mapping of atopy individuals
• One locus, on chromosome 5q,
• linked to a region that encodes a variety of
cytokines, including IL-3, IL-4, IL-5, IL-9, IL-13,
and GM-CSF.
• A second locus, on chromosome 11q
• linked to a region that encodes the chain of the
high-affinity IgE receptor.
• atopy is multigenic
• other loci to be identified

52. Lab Diagnosis of Allergy
• Skin Prick Test
• Liquid with allergen are
injected with tiny needle
either directly or by affixing
a patch
• after 24 to 72 hours to see
if a reaction occurs.
• If the skin reacts, a red,
raised area (called a wheal)
can be observed, indicating
sensitization to that allergen.

55. • The panel chosen should be based on the patient's clinical
history, as with skin testing.

56. Ig E blood levels
• IgE Blood Test
• specific immunoglobulin E (IgE) antibodies in the blood
that are produced by the body’s immune system when an
allergen is present

57. In Vitro Testing
• patients with affected skin, such as dermatographism or
atopic dermatitis.
• safer option if the patient is at risk for anaphylaxis
• Immunoassays are often referred to as radioallergosorbent
(RAST) testing, but that term is outdated because radiation
is rarely used today.
• Current methods include enzyme-linked immunosorbent
assay (ELISA)
• fluorescent enzyme immunoassays (FEIA)
• Chemiluminescent immunoassays,

58. A solid-phase immunoassay
• allergen bound to a matrix. The patient’s serum is added
and the antibodies bind to the allergen.
• All serotypes (IgG, IgM, IgA, and IgE) will bind if they
recognize the allergen.
• A secondary anti-IgE antibody is used to identify if IgE is
bound.
• The report is a quantitative value in kIUA/L or in arbitrary
divisions into classes I-VI. Asymptomatic sensitization is
common below class III (< 3.5 kIUA/L).[7]

59. • The accuracy of immunoassays varies
with the system used and the quality of
the allergen.
• There is good predictive value (>90%) for
pollens of grass, trees, dust mites, and
cats, whereas
• less accurate results may be obtained from
venoms, weeds, latex, dogs, and molds
• If results are equivocal, further evaluation
can be done by means of skin testing and,
if indicated, a challenge to the allergen.

60. Patch Testing
• chronic eczematous conditions contributing to a delayed-
type hypersensitivity reaction.
• contact dermatitis to jewelry containing nickel.
• food allergies in eosinophilic esophagitis and some drug
allergies
• The most common patch techniques are the individual Finn
chamber or the thin-layer rapid-use epicutaneous (TRUE)
test.

61. Other tests with no clinical significance
• cytotoxic tests,
• provocation-neutralization,
• electrodermal testing,
• applied kinesiology,
• iridology, and hair analysis.

62. Bibliography
• The Pathophysiology, Diagnosis and Treatment of
Allergic Rhinitis Allergy Asthma Immunol Res.
2010 April;2(2):65-76.
• The history of the idea of allergy J. M. Igea Allergy
2013; 68: 966–973.
• Hypersensitivity Mechanisms: An Overview
www.columbia.edu/itc/hs/medical/pathophys/immun

63. Thank you