MHC new

Summary

This lecture discusses the Major Histocompatibility Complex (MHC) and its role in the immune system. MHC helps the immune system distinguish between 'self' and 'non-self' antigens. It introduces two classes of MHC: Class I, which interacts with CD8 cytotoxic T cells, and Class II, which interacts with CD4 helper T cells. The lecture also covers how MHC proteins are activated in response to foreign antigens, playing a crucial role in immune responses such as organ transplant rejection and pathogen elimination. The importance of MHC in both recognizing foreign substances and regulating immune responses is emphasized.

Takeaways

• 📜 The Major Histocompatibility Complex (MHC) is crucial for immune system recognition and helps distinguish self from non-self molecules.
• 🛡️ The immune system uses MHC proteins to present antigens and neutralize foreign bodies, eliminating harmful invaders.
• 🔍 MHC helps immune cells recognize antigens, and cytotoxic T cells (CD8) are crucial in destroying infected cells.
• 🧬 MHC is classified into two types: MHC Class I (presents antigens to CD8 cells) and MHC Class II (presents antigens to CD4 cells or helper T cells).
• 🧠 The immune system can distinguish between self-cells and non-self cells due to the unique markers of MHC proteins.
• 🔬 MHC Class I molecules present antigens from intracellular pathogens (e.g., viruses), leading to the activation of cytotoxic T cells.
• 🦠 MHC Class II molecules are essential in presenting antigens from extracellular sources (e.g., bacteria) to helper T cells, activating macrophages and B cells.
• 🩺 MHC plays a key role in organ transplants and blood transfusions, where mismatched MHC can trigger rejection of foreign tissues.
• ⚙️ MHC proteins are encoded by specific genes that are activated during antigen recognition and infection, initiating immune responses.
• 💡 Helper T cells (CD4) and cytotoxic T cells (CD8) are activated by MHC Class II and Class I molecules, respectively, driving immune responses against pathogens.

Q & A

What is the main role of the immune system as described in the transcript?

The immune system functions as the body's defense system, eliminating or neutralizing foreign substances (antigens) that enter the body, ensuring they are removed.

What is MHC, and why is it important for the immune system?

MHC (Major Histocompatibility Complex) is a protein complex that helps the immune system recognize foreign molecules (antigens). It plays a critical role in differentiating between self and non-self molecules, which is vital for immune response.

How does the immune system differentiate between 'self' and 'non-self' molecules?

The immune system recognizes 'self' molecules as part of the body and 'non-self' molecules as foreign invaders through MHC markers. These markers help distinguish between the body’s own cells and foreign antigens.

What is the difference between MHC Class I and MHC Class II molecules?

MHC Class I molecules present antigens to CD8 T cells (cytotoxic T cells) and are found on almost all nucleated cells, while MHC Class II molecules present antigens to CD4 T cells (helper T cells) and are mainly found on antigen-presenting cells like macrophages and dendritic cells.

How are antigens processed and presented by MHC Class I and MHC Class II molecules?

MHC Class I molecules present antigens derived from intracellular pathogens like viruses, while MHC Class II molecules present antigens from extracellular pathogens that have been engulfed and broken down by antigen-presenting cells.

What cells function as Antigen-Presenting Cells (APCs) in the immune response?

Macrophages, dendritic cells, and activated B cells act as Antigen-Presenting Cells (APCs), which process and present antigens to T cells, helping activate the immune response.

What is the role of CD8 T cells in the immune system?

CD8 T cells, also known as cytotoxic T cells, play a role in killing infected cells by recognizing antigens presented by MHC Class I molecules. They release enzymes like perforin and granzyme to destroy the infected cells.

How do MHC Class I molecules contribute to the immune response against intracellular infections?

MHC Class I molecules present fragments of intracellular pathogens, such as viruses, to CD8 T cells. This leads to the activation of these T cells, which then kill the infected cells.

What happens during an organ transplant if the MHC markers do not match between the donor and recipient?

If the MHC markers between the donor and recipient do not match, the immune system will recognize the transplanted organ as foreign and initiate a rejection response, attacking the organ as it would an antigen.

What is the role of MHC Class II molecules in the immune response to extracellular pathogens?

MHC Class II molecules present antigens from extracellular pathogens, like bacteria, to CD4 T cells (helper T cells). This activates other immune cells, like macrophages and B cells, to combat the infection.