Type IV Hypersensitivity - Delayed type hypersensitivity
#immunology #hypersensitivity #pathology Type IV hypersensitivity reaction is a T-cell mediated response primarily caused by CD4+ T cells, though these reactions can also be caused by CD 8+ T cells. Watch other videos of the Hypersensitivity series: 💡Type I Hypersensitivity - https://youtu.be/uW96-mBFGag 💡Type II Hypersensitivity - https://youtu.be/xllsDG2PXIk 💡Type III Hypersensitivity - https://youtu.be/iY57dq7oU2U 💻Website: https://www.hackdentistry.com/ 📰Blog: https://hackdentistry.substack.com/ 📝Purchase: https://www.hackdentistry.com/pages/pricing Study resources on our website 📖All Access Bundle - https://www.hackdentistry.com/bundles/all-access-premium 📖Oral pathology Revision Ninja (Notes, Videos & MCQs) - https://www.hackdentistry.com/bundles/oral-pathology-revision-ninja 📖Oral Histology Revision Ninja (Notes, Videos & MCQs) - https://www.hackdentistry.com/bundles/revision-ninja-oral-histology 📖Periodontics Revision Ninja (Notes & MCQs) - https://www.hackdentistry.com/bundles/perio-rn 📖Question Bank - https://www.hackdentistry.com/bundles/question-bank References and further reading: 💡Kumar V, Abbas AK, Fausto N, Aster JC. Robbins Basic Pathology. 10th ed. Elsevier; 2018. 💡Kumar V, Abbas AK, Fausto N, Aster JC. Robbins and Cotran – Pathologic Basis of Disease. 8th Edition. Saunders Elsevier; 2010. 💡Abbas AK, Litchman AH, Pillai S. Cellular and Molecular Immunology. 8th Edition. Saunders Elsevier; 2015. 💡Kindt TJ, Goldsby RA, Osborne BA, Kuby J. Kuby immunology. 6th ed. New York: W.H. Freeman; 2007. Log in to https://www.hackdentistry.com and get access to: I) Numerous Notes/Cheatsheets and Videos II) Thousands of quiz questions from our vast Question Bank! HackDentistry is an edtech company that aims make learning dentistry fun,engaging and light hearted. 1) It focuses on helping students understand and retain core concepts in dentistry through highly visual sketch/whiteboard style video animations. 2) The platform helps improve exam performance by providing Revision Bundles and allowing students to test themselves using thousands of Practice Questions from a vast Question Bank. (multiple choice format). 3) It also provides for a community platform where students can come together, and engage with fellow dental students and dentists across the globe! Facebook: https://www.facebook.com/hackdentistry Instagram: https://www.instagram.com/hack.dentistry/ Twitter: https://twitter.com/hckdentistry
Type IV Hypersensitivity - Delayed type hypersensitivity
New Section
The immune system and hypersensitivity reactions.
The Immune System
- The immune system protects the human body against disease by dispatching immune cells when encountering foreign material or antigens.
- These immune cells elicit an inflammatory response to remove the foreign antigen without causing much damage to the host.
Hypersensitivity Reactions
- Under certain conditions, the host may have an exaggerated or inappropriate immune response to a foreign antigen, causing damage to host tissues.
- Hypersensitivity reactions are categorized into four types: Type I, Type II, Type III, and Type IV hypersensitivity.
- Type IV hypersensitivity is a T-cell mediated response primarily caused by CD4+ T cells but can also be caused by CD8+ T cells.
- It is also known as delayed type hypersensitivity due to its delayed onset of reaction.
Type IV Hypersensitivity Reaction
- Type IV hypersensitivity starts with a sensitization phase where an individual is first sensitized to an external agent or antigen.
- During this phase, the antigen presenting cell (APC), usually Langerhans cell or dendritic cell, presents the antigen to a CD4+ T cell via MHC II molecule.
- On presentation of the antigen, the CD4+ T cell recognizes it through its T cell receptor and differentiates into different T helper cell subtypes depending on certain cytokines present in the environment.
- In type IV hypersensitivity reactions, differentiation is usually skewed towards TH1 subset of CD4+ T cells.
Effector Phase of Type IV Hypersensitivity
- Subsequent exposure to the antigen forms the effector phase of the reaction with manifestations peaking at around 48-72 hours after second exposure.
- The antigen is picked up by the APC and presented to the TH1 cell, which triggers a cascade of reactions.
- The TH1 cell produces cytokine IFN-γ, which activates macrophages, making them super active and alert.
- Activated macrophages have better antigen presenting abilities, increased MHC II expressions, and improved phagocytosing capabilities.
- Activated macrophages produce pro-inflammatory cytokines like IL-1 and TNF-α, causing leukocytes to leak out of nearby blood vessels.
Granulomatous Infections
- In chronic granulomatous infections like tuberculosis and sarcoidosis, the persisting antigen causes a continuous loop of TH1 cells activating macrophages via IFN-γ and macrophages activating TH1 cells via IL-12.
- Constant activation of macrophages by IFN-γ causes them to transform into epithelioid cells and may form multinucleate giant cells.
- The accumulation of these cells surrounded by lymphocytes and fibrosis forms a granuloma.
CD8+ T Cell Mediated Hypersensitivity
- CD8+ T cells mediate hypersensitivity reactions in autoimmune diseases like Type I diabetes and rheumatoid arthritis, graft rejections, and viral infections.
- CD8+ T cells damage cells expressing the offending antigen through their cytotoxic activity.
Conclusion
The immune system protects the body against disease through various mechanisms. Hypersensitivity reactions can occur when there is an exaggerated or inappropriate immune response to foreign antigens. Type IV hypersensitivity is a T-cell mediated response primarily involving CD4+ T cells. It starts with sensitization followed by an effector phase where activated macrophages play a crucial role. Granulomatous infections involve persistent antigens leading to the formation of granulomas. CD8+ T cells mediate hypersensitivity in certain conditions.