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1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart2h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

21. The Immune System

Major Histocompatibility Complex Molecules

21. The Immune System

Major Histocompatibility Complex Molecules: Videos & Practice Problems

Video Lessons Practice Worksheet

Topic summary

Major histocompatibility complexes (MHCs) are crucial surface proteins on host cells that present antigens to T cells, enabling the immune system to distinguish between healthy and infected cells. There are two classes: MHC class I, found on all nucleated cells, presents endogenous antigens to cytotoxic T cells, while MHC class II, located on antigen-presenting cells (APCs) like dendritic cells and macrophages, presents exogenous antigens to helper T cells. This interaction is vital for generating appropriate immune responses against pathogens.

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Major Histocompatibility Complexes

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Major Histocompatibility Complexes Video Summary

The immune system relies on the ability of immune cells to accurately identify threats, such as infected host cells and pathogens, while avoiding healthy cells. A crucial component in this identification process is the interaction between T cells and major histocompatibility complexes (MHCs). MHCs are surface proteins found on host cells that play a vital role in presenting antigens to T cells, enabling them to initiate an appropriate immune response.

To illustrate this, consider a macrophage, a type of host cell, which displays MHCs on its surface. These MHCs present antigens—substances that can provoke an immune response—to T cells. Specifically, helper T cells, also known as CD4 cells, utilize their T cell receptors (TCRs) to recognize the MHC-antigen complex. This recognition is essential for the helper T cells to activate and orchestrate a targeted immune response against the identified threats.

There are two primary types of major histocompatibility complexes, each playing distinct roles in the immune response. Understanding these types will enhance our comprehension of how the immune system functions and responds to various challenges. As we delve deeper into this topic, we will explore the specific functions and mechanisms of these MHC types.

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Classes of MHC Molecules

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Classes of MHC Molecules Video Summary

The immune system utilizes Major Histocompatibility Complex (MHC) molecules to present antigens, which are crucial for the activation of T cells. There are two primary classes of MHC molecules: MHC class I and MHC class II, each serving distinct roles in immune response.

MHC class I molecules are present on all nucleated cells and are responsible for presenting endogenous antigens, which originate from within the cell. These antigens often include viral proteins produced by infected cells. The recognition of these antigens is facilitated by cytotoxic T cells (TC cells), specifically those expressing the CD8 marker. When a TC cell identifies an antigen presented by MHC class I, it can initiate an immune response to eliminate the infected cell.

In contrast, MHC class II molecules are found exclusively on antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells. These molecules present exogenous antigens, which are derived from outside the host cell. Helper T cells (TH cells), marked by the CD4 marker, recognize these exogenous antigens. Upon recognition, TH cells activate and orchestrate the immune response, aiding in the activation of other immune cells.

It is important to note that while APCs possess both MHC class I and MHC class II molecules, the latter is specifically involved in presenting antigens to helper T cells. The interaction between T cells and MHC molecules is guided by their respective CD markers, ensuring that CD8+ TC cells interact with MHC class I and CD4+ TH cells interact with MHC class II.

In summary, MHC class I molecules are crucial for presenting endogenous antigens to cytotoxic T cells, while MHC class II molecules present exogenous antigens to helper T cells. This distinction is vital for the immune system's ability to recognize and respond to various pathogens effectively.

Problem

Which markers are found on all nucleated cells?

MHC class I.

MHC class II.

CD4.

CD8.

Problem

MHC class II molecules are found on:

Basophils & macrophages.

B cells & Neutrophils.

Macrophages & Dendritic cells.

T helper cells & Macrophages.

All antigen presenting cells (APCs).

Problem

Once an MHC II molecule on an APC presents an antigen:

Effector cells with CD8 markers activate the APC.

Effector cells with CD4 kill the APC.

Effector cells with CD8 kill the APC.

Effector cells with CD4 activate the APC.

Problem

If an effector CD4 cell encounters an antigen presented on a MHC Class II molecule, how would it respond?

Send signals to the APC trigger apoptosis in the APC.

Engulf the APC and degrade the infected cell and the intracellular pathogen.

Send signals to the APC, activating the APC and triggering an immune response.

All of the following are possible responses of the effector CD4 cell.

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Here’s what students ask on this topic:

What are major histocompatibility complex (MHC) molecules?

Major histocompatibility complex (MHC) molecules are surface proteins found on host cells that play a crucial role in the immune system. They present antigens to T cells, enabling the immune system to distinguish between healthy and infected cells. There are two main classes of MHC molecules: MHC class I and MHC class II. MHC class I molecules are found on all nucleated cells and present endogenous antigens to cytotoxic T cells. MHC class II molecules are located on antigen-presenting cells (APCs) like dendritic cells and macrophages and present exogenous antigens to helper T cells. This interaction is essential for generating appropriate immune responses against pathogens.

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

MHC class I and MHC class II molecules differ in their distribution, the type of antigens they present, and the T cells they interact with. MHC class I molecules are found on all nucleated cells and present endogenous antigens, which originate from inside the cell, to cytotoxic T cells (CD8+). In contrast, MHC class II molecules are found only on antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells. They present exogenous antigens, which originate from outside the cell, to helper T cells (CD4+). This distinction is crucial for the immune system to target infected cells and pathogens effectively.

How do MHC molecules present antigens to T cells?

MHC molecules present antigens to T cells by displaying peptide fragments on the cell surface. MHC class I molecules present endogenous antigens, derived from proteins within the cell, to cytotoxic T cells (CD8+). These antigens are typically from intracellular pathogens like viruses. MHC class II molecules present exogenous antigens, derived from extracellular sources, to helper T cells (CD4+). These antigens are usually from extracellular pathogens like bacteria. The T cell receptor (TCR) on T cells recognizes the antigen-MHC complex, leading to the activation of the T cell and the initiation of an immune response.

What types of cells express MHC class II molecules?

MHC class II molecules are expressed on antigen-presenting cells (APCs), which include dendritic cells, macrophages, and B cells. These cells are specialized in capturing, processing, and presenting exogenous antigens to helper T cells (CD4+). Unlike MHC class I molecules, which are found on all nucleated cells, MHC class II molecules are restricted to these specific immune cells. This selective expression allows for a targeted immune response, as helper T cells can recognize and respond to antigens presented by APCs, leading to the activation of other immune cells and the coordination of the immune response.

Why are MHC molecules important for the immune system?

MHC molecules are essential for the immune system because they enable the recognition and differentiation of self from non-self. By presenting antigens to T cells, MHC molecules help the immune system identify and target infected or abnormal cells while sparing healthy cells. MHC class I molecules present endogenous antigens to cytotoxic T cells, which can then destroy infected cells. MHC class II molecules present exogenous antigens to helper T cells, which coordinate the activation of other immune cells. This antigen presentation is crucial for initiating and regulating immune responses, ensuring that the body can effectively combat infections and diseases.