Células Apresentadoras de Antígenos - APC

Summary

This video explains the role of antigen-presenting cells (APCs) in the immune system, focusing on dendritic cells, macrophages, and B lymphocytes. These specialized cells express both MHC class I and II proteins, enabling them to present antigens to T lymphocytes (CD4+ and CD8+). Dendritic cells activate naïve T cells in lymph nodes, while macrophages and B cells engage effector T cells at infection sites. The lecture details the complex processes of antigen uptake, digestion, and presentation, and emphasizes the importance of these interactions in immune responses and activation.

Takeaways

• 😀 APCs (Antigen-Presenting Cells) like dendritic cells, macrophages, and B cells are critical for activating the immune system by presenting antigens to T cells.
• 🦠 Dendritic cells are considered the most important APCs for initiating immune responses by presenting antigens to naïve T cells in the lymph nodes.
• 💪 Macrophages present antigens to effector T cells at sites of infection, playing a vital role in immune defense at the infection site.
• 🔬 B cells also act as APCs, presenting antigens to activated T cells both in lymph nodes and peripheral tissues.
• 🧬 MHC (Major Histocompatibility Complex) proteins are essential for antigen presentation. MHC Class 1 presents antigens to CD8+ T cells, and MHC Class 2 presents antigens to CD4+ T cells.
• 🧑‍🔬 CD4+ T cells differentiate into various subtypes, such as Th2 and Th17, which perform specialized functions in acquired immunity.
• ⚔️ The interaction between APCs and T cells is bidirectional: activated T cells stimulate APCs (like macrophages and B cells) to enhance immune responses.
• 🔄 The process of antigen presentation involves the capture, processing, and presentation of antigens by APCs using MHC molecules.
• 🔬 Dendritic cells have low-specificity receptors for antigen capture, whereas B cells use high-specificity antibodies for antigen binding.
• 🔑 The antigen presentation process is crucial for immune recognition, as T cells require specific receptors (TCRs) to match antigens presented by APCs.

Q & A

What are Antigen-Presenting Cells (APCs)?

Antigen-Presenting Cells (APCs) are specialized cells that present fragments of antigens to T lymphocytes. They express MHC class I or II proteins on their surface, enabling them to present antigens to different types of T cells.

Which cells are considered professional APCs?

The professional APCs are dendritic cells, macrophages, and B lymphocytes. These cells express both MHC class I and class II proteins, allowing them to present antigens to both CD8+ and CD4+ T cells.

What is the role of MHC class I and class II proteins in antigen presentation?

MHC class I proteins present antigens to CD8+ T cells, while MHC class II proteins present antigens to CD4+ T cells. These proteins play a critical role in immune response, particularly in transplant rejection.

How do dendritic cells present antigens to T cells?

Dendritic cells present antigens to T cells in the lymph nodes, specifically to virgin (naive) T cells. They use MHC class II proteins to present the antigen to CD4+ T cells, which can then differentiate into various subtypes.

Where do macrophages present antigens?

Macrophages present antigens at infection sites. They present antigens to effector T cells, which have already been activated during an immune response.

How do B lymphocytes present antigens?

B lymphocytes present antigens to activated CD4+ T cells in the lymph nodes and other tissues. This interaction is crucial for activating the B cells, which then produce antibodies against the pathogen.

What is the difference between how dendritic cells and macrophages present antigens?

Dendritic cells present antigens to virgin CD4+ T cells in lymph nodes, while macrophages present antigens to activated T cells at infection sites. Both use MHC class II proteins to present the antigen.

What happens after an APC presents an antigen to a T cell?

After an APC presents an antigen to a T cell, the T cell's receptor (TCR) binds to the antigen-MHC complex. This binding activates the T cell, which can then initiate an immune response, either by attacking infected cells or stimulating other immune cells.

How do dendritic cells capture antigens?

Dendritic cells capture antigens using receptors on their surface that have low specificity. Upon binding an antigen, they perform phagocytosis and process the antigen in lysosomes to present it via MHC class II molecules.

What is the significance of the CD4 and CD8 proteins on T cells?

CD4 and CD8 are co-receptors on T cells that help recognize specific MHC molecules. CD4+ T cells interact with MHC class II molecules, while CD8+ T cells interact with MHC class I molecules. This interaction is crucial for activating the T cells during immune responses.