Type Iv Hypersensitivity

Type Iv Hypersensitivity


Introduction

  • Cell-Mediated) Reactions/Delayed-type hypersensitivity/antibody-independent
  • Involve reactions by memory cells.
  • First contact sensitizes person.
  • Subsequent contacts elicit a reaction.
  • Reactions are delayed by one or more days (delayed type hypersensitivity).
  • Delay is due to migration of macrophages and T cells to site of foreign antigens.
  • Reactions are frequently displayed on the skin:  itching, redness, swelling, pain.
  • Tuberculosis skin test
  • Poison ivy
  • Metals
  • Latex in gloves and condoms (3% of health care workers)

Peak action time

  • after 24 hours
  • Anaphylactic shock may occur 

Initiated by

  •  activated T-lymphocytes.

 Includes

  • Delayed type hypersensitivity – mediated by CD-4 T cells.
  • T-cell mediated cytotoxicity – mediated by CD8- T cells.

Delayed type hypersensitivity

 

  • CD-4 T cells and macrophages are primarily involved
  • Mechanism of defence against various intracellular pathogens
  • mycobacteria
  • fungi
  • certain parasites.
  • Pathophysiology
  • Characterized by formation of granuloma
  • a localized mass that contains activated macrophages (epitheloid) cells 
  • surrounded by collar of lymphocytes and giant cells.
  • It is also called granulomatous inflammation.
  • Antigen presenting cell comes in contact with naive CD-4 T cells
  • Naive CD-4 T cells recognize these peptide antigens in association with MHC – II and differentiate in to T4-1 cells.
  • Expression of delayed hypersensitivity largely depends on the cytokines secreted by T4-1 cells.

 T-cell mediated cytotoxicity

  • In this type of hypersensitivity, cytotoxic T cells kill virus infected or tumor cells.
Examples
  • Tuberculin test
  • Lepromin test
  • Fairleys (Schistosomiasis) test
  • Frie’s (LGV) test
  • Granulomatous inflammation
  • Contact dermatitis
  • Defence against intracellular pathogen
  • Type I lepra reaction
  • Graft rejection
  • Resistance to virus infection
  • Reaction  against tumour cells

Type IV hypersensitivity Test

  • Injection is given intradermally on the flexor aspect of the forearm.
  • The site is examined after 48-72 hours.
  • Induration of greater than 10 mm is considered as positive.
  • Examples → Tuberculin test, Lepromin test
Exam Question
 

Introduction

  • Cell-Mediated) Reactions/Delayed-type hypersensitivity/antibody-independent
  • Involve reactions by memory cells.
  • Reactions are delayed by one or more days (delayed type hypersensitivity).
  • Delay is due to migration of macrophages and T cells to site of foreign antigens.
  • Reactions are frequently displayed on the skin:  itching, redness, swelling, pain.

Peak action time

  • after 24 hours 

Initiated by

  • activated T-lymphocytes.

 Includes

  1. Delayed type hypersensitivity – mediated by CD-4 T cells.
  2. T-cell mediated cytotoxicity – mediated by CD8- T cells.
Examples
  • Tuberculin test
  • Lepromin test
  • Fairleys (Schistosomiasis) test
  • Frie’s (LGV) test
  • Granulomatousinflammation
  • Contact dermatitis
  • Defence against intracellular pathogen
  • Type I lepra reaction
  • Graft rejection
  • Resistance to virus infection
  • Reaction  against tumour cells

Type IV hypersensitivity Test

  • Injection is given intradermally on the flexor aspect of the forearm.
  • The site is examined after 48-72 hours.
  • Induration of greater than 10 mm is considered as positive.
  • Examples → Tuberculin test, Lepromin test
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