Allergy (1)

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ALLERGY
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ALLERGY

• An altered response (different from the normally
  seen) to an offending agent
• Atopy
• Hypersensitivity

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Manifestations

• Rhinitis
• Asthma
• Urticaria
• Eczematous (atopic dermatitis)
• Anaphylaxis
• (Alone or combinations)
• Systemic mastocytosis

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Anaphylactic materials

• Heterologous proteins
• Hormones (Ins, VP, PTH)
• Enzymes (Tryp, CT, Pnc, SK)
• Pollen extracts
• Non-pollen extracts
• Foods (milk, eggs, sea food)
• Antisera
• Occupation related proteins
• Hymenopetra venom

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• Polysaccharides
• Dextran
• Thiomerosal (vaccine preservative)
• Drugs Protamine
• Antibiotics
• Local anaesthetics
• Muscle relaxants
• Vitamins
• Diagnostic agents
• Occupation related chemicals
• Ethylene oxide

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Mechanism of Allergy

• Sensitization Childhood or early
  adolescence
• Activation on re-exposure
• Antigen specific

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Activation

• Antigen exposure (re)
• ?
• Sensitized key
• effector cells
• (Mst cells, basophils)
• ? ? IgE fixation
• Ag specific activation
• ?
• Mediator release
• Lipids LTB4 Secretory granule Cytokines
• LTC4, PAF, (preformed) IL-3, IL-4, IL-5,
• PGD2 Hist, Proteoglycans, IL-6, GM-CSF, IL-1,
• tryptase, chymase INFr, TNF ?

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Immune Reaction
Onset Immunological Allergen quantity Clinical features Immediate lt Minutes IgE dependent Preformed mediators Minute Pruritis rhinorrhoea bronchospasm wheal and flare bronchorrhoea Late 4-6 hours Cellular cytokines Greater Nasal block skin erythema induration ? PFT (BHR)
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Sensitization

• Antigen exposure
• ?
• Processing by Ag presenting cells
• ?
• Presentation via their MHC to
• T cell subsets
• ?
• Recognition response
• IL-4 TH2 response IN Fr TH1 type
• ?
• Activation of specific Allergen specific
• B cells ? Plasma
  cells ? IgE
• ?
• Sensitization of IgE Fc receptor bearing
  cells

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Characteristics

• Immediate/Late
• Sudden/Episodic
• Recurrent/Persistent
• Spontaneous remissions/recurrences
• Familial
• Variable

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ANAPHYLAXIS

• Life threatening response of a sensitized person,
  immediately after specific antigen exposure.
• Respiratory distress
• Vascular collapse

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Predisposing Factors

• Immunogen exposure
• No proven influence
• -Age, sex, race
• -Occupation, place
• -Atopy (for Penicillin
• therapy or insect bites)

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Diagnosis of Allergy

1. Circumstantial Onset antecedent admn.
2. Specific history e.g. recurrence
3. Skin tests
4. Specific tests disease directed/others

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Treatment of Allergy

• General Identifying allergenic agents
• Antihistaminics
• Glucocorticoids
• Topical
• Oral
• Parenteral
• Specific
• Immunotherapy

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Treatment of Anaphylaxis

• Early recognition
• Epinephrine
• - S/C 0.2 0.5 ml of 11000 ml
• Repeated doses.
• - In to the site/tourniquet
• - I.V infusion, 2.5 ml of 110,000 at
• 5 to 10 min
• Volume expanders N. saline
• Vasopressors dopamine
• Isoproterenol (1200) 0.5 ml

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Tmt. (contd.)

• Oxygen, Intermittent PPB
• Endotrach. Intubation/tracheostomy
• Ancillary agents
• Antihistaminics diphenyl hydramine
• (50-100 mg) I/M or I/V
• Aminophylline (0.25 0.5 gm), I/V
• Glucocorticoids I/V esp. for later recurrence

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Prevention of Anaphylaxis

• History of previous episodes
• Cross reactivity of agents
• Skin test scratch/I.D.
• Allergenic extracts
• Penicillins/other agents
• Desensitization slow vs rapid
• Resuscitation facilities

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Protection against venom induced anaphylaxis

• Immunotherapy Use of specific/cross reacting
  venom
• Modification of outdoor activities dress and
  habits
• Informational bracelet
• Epinephrine kit

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Manifestations

• Onsetwithin seconds
• Laryngeal oedema Lump, hoarseness, stridor
• Bronchospasm
• Cutaneous wheals, giant hives
• Schimitar syndrome
• Fatal cases Angio oedema (skin upper respir.
  tract, viscera) shock

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Diagnosis of Anaphylaxis

• Clinical picture
• Prausnitz-Kustner reaction Passive transfer of
  cutaneous hypersensitivity
• Passive sensitization of a human leukocyte
  suspension
• Radioimmunoassay for specific IgE antibodies
• Elevation of beta tryptase levels i.e. mast cell
  activation

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Antihistaminic agents

• H1 receptor antagonists
• Chlorphenirmine
• Diphenyl hydramine
• Astemizole, terfenatine
• Non sedating cetrizine, loratadine,
  fexofenadine
• Both H1 and H2 agents Doxepin
• Others Cyproheptadine, Hydroxyzine
• Alpha adrenergic agents Phenyl epherine
  (Topical)
• Mast cell stabilizers Cromolyn

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Systemic Mastocytosis

• Mast cell hyperplasia
• Indolent cutaneous
• features, vascular collapse,
• ulcer dis, hepatospleno, LN
• Concomitant haematological dis
• Aggressive
• Mastocytic leukaemia

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