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Hypersensitivity Reactions | Medical Science Optional Notes for UPSC PDF Download

Introduction

  • The protective immune responses can, at times, lead to tissue damage.
  • Hypersensitivity encompasses immune reactions causing injury, resulting in hypersensitivity diseases.
  • Traditionally, hypersensitivity reactions are categorized into four types, each associated with the principal immune mechanism causing injury. Three involve variations in antibody-mediated injury, while the fourth is T cell-mediated.

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Type I Hypersensitivity

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Question for Hypersensitivity Reactions
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Which type of hypersensitivity reaction is associated with antibody-mediated injury?
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Type II Hypersensitivity

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Type III Hypersensitivity

Immune Complex Formation

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Immune Complex Deposition

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Immune Complex-Mediated Inflammation and Tissue Injury

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Type IV Hypersensitivity

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Gell and Coombs classification of hypersensitivity reactions

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Type V/VI Hypersensitivity

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Natural Killer Cells

  • 10-15% of peripheral lymphocytes
  • Lack TCR/Cell surface Ig
  • Contain abundant azurophilic granules (Large granular lymphocytes)
  • Constituent of the innate immune system (No prior sensitization required)
  • CD16/CD56+ (Specific to NK cells)
  • Capable of lysing IgG-coated target cells through ADCC
  • NK cells possess two types of receptors— inhibitory and activating.
  • Inhibitory receptors recognize self class I MHC molecules present on all healthy cells, while activating receptors identify molecules expressed or upregulated on stressed, infected, or DNA-damaged cells.
  • Typically, the inhibitory receptors outweigh the activating ones, preventing NK cell activation.

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

Question for Hypersensitivity Reactions
Try yourself:
What is the main function of natural killer (NK) cells in the immune system?
View Solution

ADCC

Hypersensitivity Reactions | Medical Science Optional Notes for UPSC

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FAQs on Hypersensitivity Reactions - Medical Science Optional Notes for UPSC

1. What are natural killer cells?
Ans. Natural killer (NK) cells are a type of immune cell that plays a crucial role in the body's defense against infections and cancer. They are part of the innate immune system and are capable of recognizing and killing infected cells or cancer cells without the need for prior exposure or activation.
2. How do natural killer cells work?
Ans. Natural killer cells work by recognizing the presence of abnormal cells, such as infected cells or cancer cells, through a process called "missing-self recognition." They have receptors that can detect changes in the surface proteins of these abnormal cells, allowing the NK cells to directly kill them or release molecules that trigger other immune responses against them.
3. What is the role of natural killer cells in hypersensitivity reactions?
Ans. In hypersensitivity reactions, such as allergic reactions, natural killer cells play a regulatory role. They can modulate the immune response by producing cytokines that either enhance or suppress the allergic reaction. Additionally, NK cells have been implicated in certain types of hypersensitivity reactions, such as drug-induced hypersensitivity.
4. How are natural killer cells activated?
Ans. Natural killer cells can be activated through various mechanisms. They can be directly activated by the recognition of specific surface proteins on target cells, which triggers their cytotoxic activity. They can also be indirectly activated by cytokines released by other immune cells, such as interferons or interleukins, which enhance their killing capacity.
5. Can natural killer cells be targeted for therapeutic interventions?
Ans. Yes, natural killer cells can be targeted for therapeutic interventions. Researchers are exploring various strategies to enhance the activity of NK cells against cancer cells, such as using immunotherapies that boost NK cell function or genetically engineering NK cells to express chimeric antigen receptors (CAR-NK cells). These approaches show promising results in preclinical and clinical studies and hold potential for future cancer treatment options.
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