31. Immunology 2 – Memory, T cells, & Autoimmunity

TL;DR

The immune system can recognize and respond to foreign antigens through antigen presentation on MHC molecules, but it needs mechanisms to avoid attacking self-antigens and causing autoimmune diseases.

Transcript

PROFESSOR: All right. So today, we're going to talk about immunity again. And so this movie up on the screen here-- this is a cell. You can see the outline of the cells kind of around here. That's the outline of the cell. But what you can see is that there is something in the cell moving around, and that is an intracellular bacteria called listeria... Read More

Key Insights

• 🚀 Antigen presentation is crucial for immune cells to recognize intracellular infections and launch an immune response.
• 🏛️ MHC class 1 molecules present intracellular peptides, while MHC class 2 molecules present extracellular peptides.
• 😃 CD8 positive T cells respond to MHC class 1 molecules and kill infected cells, while CD4 positive T cells enhance B cell function.
• 👊 The immune system needs mechanisms to avoid attacking self-antigens, such as negative selection in lymphoid organs and coincident activation with innate immune responses.
• 🥺 Inhibitory receptors like CTLA4 and PD1 maintain immune system regulation, but inhibitory receptor blockade can be used as a therapy for certain cancers, leading to immune recognition and killing of tumor cells.

Questions & Answers

Q: How are antigens presented on the surface of cells for immune cells to see?

Antigens are presented through a process called antigen presentation, where peptides are displayed on the cell surface using major histocompatibility complex (MHC) molecules. This allows immune cells to recognize and respond to the antigens.

Q: What is the difference between MHC class 1 and MHC class 2 molecules?

MHC class 1 molecules are expressed on all nucleated cells and present peptides from the cytoplasm. MHC class 2 molecules are expressed on antigen-presenting cells like B cells and present peptides from the extracellular space.

Q: How do CD8 positive T cells respond to MHC class 1 molecules?

CD8 positive T cells, also known as cytotoxic or killer T cells, recognize MHC class 1 molecules and kill infected cells. They play a crucial role in controlling intracellular infections.

Q: What is the role of CD4 positive T cells in immune responses?

CD4 positive T cells, also known as helper T cells, recognize MHC class 2 molecules and enhance B cell function. They help in affinity maturation, isotype switching, and differentiation of B cells into memory cells or plasma cells.

Summary & Key Takeaways

• Immune cells need to address intracellular infections by recognizing antigens inside cells. This is done through antigen presentation, where short protein sequences (peptides) are displayed on the cell surface using major histocompatibility complex (MHC) molecules.

• MHC class 1 molecules are expressed in all nucleated cells and present peptides from the cytoplasm. They are recognized by CD8 positive T cells, also called killer or cytotoxic T cells, which can kill infected cells.

• MHC class 2 molecules are expressed on antigen-presenting cells like B cells and present peptides from the extracellular space. They are recognized by CD4 positive T cells, also called helper T cells, which enhance B cell function.