Notes on Type IV Hypersensitivity Reaction

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What is Type IV Hypersensitivity Reaction?

• Also known as cell mediated or delayed type hypersensitivity.

• Eg., tuberculin reaction (Mantoux skin test).

• Many disease are caused by Type 4 hypersensitivity: infectious diseases: tuberculosis, leprosy, blastomycosis, histoplasmosis, toxoplasmosis, leishmaniasis, etc.)

• Also causes granulomas due to foreign infections.

• Papular lesions as caused in contact dermatitis.

• There are three types of reactions: contact, tuberculin and granuloma.

• Damage is caused by T cells, monocytes and macrophages.

• Cytokines that recruit other inflammatory cells are secreted by Th1 cells.

• Diagnostic tests include: delayed cutaneous reaction ontoux test and patch test (for contact dermatitis).

• Corticosteroids and immunosuppressants unused un treatment.

• Some Type IV reactions require the presence of natural IgM antibody for initiation. Activating Th1 cells is responsible for propagating the response. It is possible that IgM-antigen complexes may recruit inflammatory cells including memory T cells.

• CD8 cytotoxic T cells and CD4 helper T cells recognize either intracellular or extracellular synthesized antigen when it is complexed with MHC I or MHC II molecules.

Additional Type IV Hypersensitivity Reaction Notes:

Macrophages function as antigen-presenting cells and release interleukin-1 which promotes the proliferation of helper T cells. Helper T cells release interferon-gamma and interleukin-2 which together regulate delayed hypersensitivity reactions centered around macrophage activation and T-cell mediated immunity. Activated cytotoxic T cells destroy target cells, such as allografts, on contact. Natural killer cells can kill target cells directly, in the absence of prior immunization and without MHC restriction, and by antibody-dependent cellular cytotoxicity (ADCC). Activated macrophages express increased phagocytic, bacteriocidal, and cytocidal activity and, when confronted with certain intracellular pathogens, undergo granulomatous transformation into epithelioid and multinucleated giant cells.

Contact Hypersensitivity:

This results from contact with certain elements like metal, salts and other reactive chemicals. The antigen must be a complex of the hapten and a self peptide.

Additional Readings:

Basic Immunology

1. Introduction to Immunology
2. Cells of Immunology
3. Selection of Lymphocytes
4. Primary Response to Antigen
5. Antigen Processing and Presentation
6. Humoral Effector Mechanism Generator
7. Cell-Mediated Effector Mechanism Generator
8. Vaccination and Immunotherapy
9. Immunodeficiency Diseases
10. Acquired Immunodeficiency Syndrome
11. Hypersensitivities and Autoimmunity Diseases
12. Immunology of Transplantation
13. Immunology of Cancer
14. Immunology Laboratory Technology
15. Acquired Immunity
16. Type II Hypersensitivity Reaction
17. Hypersensitivity Reactions
18. Primary Immunodeficiency
19. Secondary Immunodeficiency
20. Type III Hypersensitivity Reaction
21. Type IV Hypersensitivity Reaction
22. Type V Hypersensitivity Reaction
23. Tumor Immunology
24. Images of Antibodies
25. Th1 vs Th2 cells

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1. Histology of Lymphoid Tissue

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