Reconhecimento do Antígeno

Summary

In this lesson, Professor Luiz Amarante explains the immune system's mechanisms for recognizing antigens, focusing on the distinction between cellular and humoral immune responses. He explores how T lymphocytes (T cells) recognize infected cells through MHC Class I molecules in cellular immunity, and how B lymphocytes (B cells) produce antibodies in response to pathogens in humoral immunity. The presentation emphasizes the role of antigen-presenting cells and helper T cells in activating these responses, and outlines how the immune system distinguishes between self and non-self, ensuring targeted defense against pathogens and abnormal cells.

Takeaways

• 😀 The immune system can recognize molecules, cells, or microorganisms as foreign invaders or self, based on its complex mechanisms.
• 😀 Autoimmune diseases occur when the immune system mistakenly attacks the body's own cells, while cancer cells are also recognized as foreign by the immune system.
• 😀 Antigen recognition by T cells is essential for immune responses, where cytotoxic T cells recognize infected cells via antigen presentation by antigen-presenting cells (APCs).
• 😀 Antigen-presenting cells (APCs) include dendritic cells, B lymphocytes, and macrophages, which present foreign antigens to T cells after phagocytosis.
• 😀 T cell receptors (TCRs) on T cells recognize antigens presented on the surface of APCs through the major histocompatibility complex (MHC).
• 😀 MHC class I molecules are expressed by most cells, including infected cells, and present antigens to cytotoxic T cells.
• 😀 Cytotoxic T cells, once activated, undergo clonal expansion and produce cytokines to destroy infected cells.
• 😀 Humoral immunity involves B lymphocytes recognizing antigens and differentiating into plasma cells, which produce antibodies to eliminate pathogens.
• 😀 T helper cells (Th cells) play a key role in activating B cells by presenting antigens through MHC class II molecules, which helps in the antibody production process.
• 😀 In cellular immunity, cytotoxic T cells recognize infected cells directly, while in humoral immunity, B cells produce antibodies to neutralize extracellular pathogens.
• 😀 Memory cells, either T or B lymphocytes, remain long-lived (up to 20 years) and are important for recognizing antigens in future encounters, but memory formation can be impaired without helper T cell involvement.

Q & A

What is the main topic of the lesson presented by Professor Luiz Amarante?

The main topic of the lesson is the recognition of antigens by the immune system, and the basic differences between cellular immune responses and humoral immune responses.

What is the immune system's role in recognizing foreign antigens?

The immune system recognizes foreign antigens such as viruses, bacteria, fungi, protozoa, incompatible transplanted cells, and mutated cells like cancer, while distinguishing them from the body's own molecules and cells.

What happens in autoimmune diseases with regards to antigen recognition?

In autoimmune diseases, the immune system mistakenly recognizes the body’s own molecules and cells as foreign, leading to an immune response against them.

What is the role of T lymphocytes (T cells) in immune responses?

T lymphocytes are involved in recognizing infected cells and initiating immune responses. T cytotoxic cells specifically recognize and destroy infected cells through the antigen presentation process.

What is antigen presentation and which cells are responsible for it?

Antigen presentation is the process by which antigen-presenting cells (APCs) like dendritic cells and B lymphocytes process and display antigens on their surface to activate T cells, particularly T cytotoxic cells.

What are the major types of molecules involved in antigen presentation?

The major molecules involved in antigen presentation are the Major Histocompatibility Complex (MHC) molecules, specifically MHC class I and class II, which are essential for presenting antigens to T cells.

How does the T cell receptor interact with the antigen during the immune response?

The T cell receptor binds to antigens presented by MHC molecules on the surface of antigen-presenting cells. This interaction triggers an intracellular signaling cascade that activates the T cell and leads to its expansion.

How are cytotoxic T cells activated and what is their role in the immune response?

Cytotoxic T cells are activated when their receptors bind to antigens presented by MHC class I molecules on infected cells. Once activated, they produce cytokines and other substances to destroy the infected cells.

What is the role of helper T cells in humoral immunity?

Helper T cells assist in humoral immunity by activating B cells. This process involves the helper T cell recognizing antigens presented by MHC class II molecules on antigen-presenting cells, which leads to B cell activation and differentiation into plasma cells that produce antibodies.

How does the immune system respond to extracellular pathogens such as viruses?

Extracellular pathogens, such as free-floating viruses, are targeted by antibodies produced by plasma cells. These antibodies neutralize the pathogens, marking them for destruction.