Type IV Hypersensitivity |T- Cell mediated Hypersensitivity |Mechanism | Examples

Summary

This tutorial delves into type four hypersensitivity reactions, focusing on cell-mediated immunity. It explains how CD4+ T cells produce cytokines leading to chronic inflammation. The video outlines the pathogenesis of delayed-type hypersensitivity, highlighting T helper 1 and T helper 17 responses. It also covers clinical examples like tuberculin reactions and contact dermatitis, and discusses T cell-mediated cytotoxicity in diseases like type 1 diabetes and rheumatoid arthritis. The tutorial encourages active learning through practice tests on Visia, an engaging platform for medical knowledge.

Takeaways

• 🧬 Type Four Hypersensitivity, also known as cell-mediated hypersensitivity, is primarily caused by inflammation resulting from cytotoxic T cells.
• 🔬 CD4 positive T cells produce cytokines that lead to chronic inflammation, often in response to environmental or self-antigens.
• 🌟 Delayed Type Hypersensitivity (DTH) is a prototype of T-cell mediated inflammation, detectable within 24 to 48 hours post-antigen exposure.
• 🔍 T helper 1 (Th1) and T helper 17 (Th17) cells are key contributors to DTH, with Th1 promoting macrophage activation and Th17 recruiting neutrophils.
• 🛡 The pathogenesis of DTH involves the activation of CD4 positive T cells, differentiation into effector T cells, and resulting inflammation and tissue injury.
• 🔄 Upon re-exposure to an antigen, memory T cells, which are long-lived, respond quickly to prevent further inflammation.
• 💉 Clinical examples of CD4 positive T cell-mediated inflammation include tuberculin reactions and contact dermatitis.
• 🛑 In persistent antigen scenarios, such as with Mycobacterium tuberculosis, T helper one cells can lead to granuloma formation, a hallmark of granulomatous inflammation.
• 🚨 CD8 positive cytotoxic T lymphocytes kill antigen-expressing target cells through apoptosis, a key mechanism in cell-mediated immunity.
• 🏥 Diseases mediated by T cell cytotoxicity include type 1 diabetes, graft rejection, and responses against viruses and tumor cells.
• 📚 The script concludes with a summary of type four hypersensitivity, its mechanisms, and examples, encouraging active learning through practice tests and feedback on the Visia platform.

Q & A

What is type four hypersensitivity?

Type four hypersensitivity, also known as cell-mediated hypersensitivity, is primarily caused by inflammation resulting from cytotoxic T cells, which are produced by CD4 positive T cells.

What are the main cells involved in type four hypersensitivity reactions?

The main cells involved in type four hypersensitivity reactions are CD4 positive T cells, which produce cytokines leading to inflammation.

What type of inflammation is typically associated with type four hypersensitivity?

Type four hypersensitivity is most often associated with chronic inflammation.

Which T helper cells contribute to delayed type hypersensitivity?

T helper 1 (Th1) and T helper 17 (Th17) cells contribute to delayed type hypersensitivity.

What is the role of interferon gamma in T helper 1 cells?

Interferon gamma, produced by T helper 1 cells, promotes further helper cell development and activates other immune cells, such as macrophages.

How do T helper 17 cells respond to extracellular pathogens?

T helper 17 cells produce interleukin-17 and other cytokines and chemokines, which recruit more neutrophils and monocytes to promote inflammation against extracellular pathogens.

What happens to effector T cells after the inflammation is cleared?

After the inflammation is cleared, effector T cells transform into memory T cells, which are long-lived and respond quickly to the same antigen if encountered again.

What are the clinical examples of CD4 positive T cell-mediated inflammatory reactions?

Clinical examples of CD4 positive T cell-mediated inflammatory reactions include tuberculin reaction and contact dermatitis.

What is the difference between T helper 1 and T helper 17 in terms of the pathogens they target?

T helper 1 cells target intracellular pathogens, such as some bacteria and viruses, while T helper 17 cells handle extracellular bacteria and fungi.

How do activated CD8 positive cytotoxic T lymphocytes kill target cells?

Activated CD8 positive cytotoxic T lymphocytes kill target cells by inducing apoptosis, either through the Fas ligand and Fas receptor interaction or by forming a perforin and granzyme complex.

What are some diseases associated with T cell-mediated cytotoxicity?

Diseases associated with T cell-mediated cytotoxicity include type 1 diabetes, graft rejection, reactions against various viruses, and destruction of some tumor cells.