Type IV Hypersensitivity

Type 4 hypersensitivity is often called delayed type hypersensitivity as the reaction takes two to three days to develop. Unlike the other types, it is not antibody mediated but rather is a type of cell-mediated response.

CD4+ helper T cells recognize antigen in a complex with MHC II major histocompatibility complex on the surface of antigen-presenting cells. These can be macrophages that secrete IL-12, which stimulates the proliferation of further CD4+ Th1 cells. CD4+ T cells secrete IL-2 and interferon gamma, inducing the further release of other Th1 cytokines, thus mediating the immune response. Activated CD8+ T cells destroy target cells on contact, whereas activated macrophages produce hydrolytic enzymes and, on presentation with certain intracellular pathogens, transform into multinucleated giant cells.
Source Wikipedia

[kipling]

This only part of the story. There is another type IV hypersensitivity subtype that does not involve T-helper cells (CD4+), MHC-II or professional APCs such as dendritic cells or macrophages. Instead this pathway utilizes MHC-I on tissue cells that have absorbed a hapten and present the antigen directly to CD8+ cytotoxic T-cells. The cytotoxic T cells are activated and release cytokines, performs and granzymes to kill the cell directly. This is sometimes called direct T-cell mediated cytotoxicity.

[laibazahidlaibazahid]

very well explained Sir
Finally found the right video after searching a lot

[poppins]

Thank you soo much doctor, your way of explaining makes us feel the subject light, your use of colours, and your writing is really helpful.
Thank you sir

[MsSimsima]

Thank you soo much for your effort
Ireaalllly needed to understand it ..
☘🌸 جزاك الله عنا خير الجزاء

[inimitableleader]

شكرا أستاذ كثيرا على المجهود ونتمنى لو كانت الترجمة بالعربية لمساعدتنا أكثر 😊

[vishaldey]

You gave some wrong information to us, at 2:45-2 :50 u said haptens are bound to antigen and formed a immunogenic particle, but hapters are also antigens but unable to induce immune response, so they are abtigens but not immunogenic. To be immunogenic they bound to carrier protein present in affected tissues and formed conjugate protein, which acts as a immunogenic particle, and engulfed by tissue macrophages or dendritic cell... So foreign particle due to small size they act as hapten.

[sadafshakeel]

**There is a correction:**

5:12 pr jo aapne " activated macrophage secretes" btaya hai wo sb activated macrophage nhi TH1 secrete kryega

TH1 secretes: IFN gamma, TNF beta, IL-2, 3, 8.

Effects of macrophage activation:
Increase class II MHC Molecules
Increase TNF receptors
Increase oxygen radicals
Increase nitric oxide

Please correct this part, so tht students Exms m Sahi likh kr aye.

[satishdarlz]

Neat diagrams and presentation sir very easy to understand

[cosmictickle]

i know that this is an old video. I see a lot of people in the comments with vast knowledge. I believe that I have this condition with a hypersensitivity to some chemical. I have documented exposures to TCE, PCE, benzene, and vinyl chloride. I cannot find anyone with the knowledge or tools to diagnose me. I am in Alabama, but will travel and pay for someone with expertise

[evamadaan]

Isn't adjuvants increase the immnunogenicity of antigens

[-yourhydrogencyanide-]

Hello sir, so does that mean effector phase is like re-exposure of the same antigen? Thank you.