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Cell-Mediated Immunity

cell-mediated immunity
immune system

Systems Biology

Cell-mediated immunity is a part of the specific (adaptive) immune system that fights specific invaders. It utilizes T-cells to activate immune responses from other body cells. There are four types of T-cells (T-lymphocytes): helper T-cells (CD4+), cytotoxic T-cells (CD8+), memory T-cells, and regulatory T-cells. T-cells, produced in the bone marrow, move into the thymus to mature, where thymosin, a thymus protein, facilitates their development.

Helper T-cells coordinate the immune responses by releasing cytokines, which signal macrophages, plasma cells, and cytotoxic T-cells. Cytotoxic T-cells destroy infected body cells by inducing apoptosis in infected cells, reducing pathogen spread. Memory T-cells retain information about specific pathogens, responding rapidly in subsequent infections. Regulatory T-cells suppress immune responses once a pathogen is controlled and maintain self-tolerance.

The HIV virus targets helper T-cells, which impairs both cell-mediated and humoral immune responses, leading to acquired immunodeficiency syndrome (AIDS).

Lesson Outline

<ul> <li>Introduction to cell-mediated immunity</li> <ul> <li>Part of the adaptive immune system</li> <li>Uses T-cells for immune response</li> </ul> <li>T-cell development</li> <ul> <li>Produced in bone marrow</li> <li>Develop in the thymus</li> <li>Thymosin assists maturation</li> </ul> <li>Types of T-cells</li> <ul> <li>CD4+ T-cells (helper T-cells)</li> <li>CD8+ T-cells (cytotoxic T-cells)</li> <li>Memory T-cells</li> <li>Regulatory T-cells</li> </ul> <li>T-cell differentiation in the thymus</li> <ul><li>Antigen-presenting cells (APCs) display self-proteins for selection</li> <li>Positive and negative selection</li> <ul> <li>Positive selection: Antigen-Presenting Cells (APCs) in the thymus display self-proteins to T-cells</li> <li>Negative selection: T-cells that strongly react to self-proteins are eliminated through apoptosis</li> </ul> </ul> <li>Major histocompatilibity complex (MHC) proteins' role in communication</li> <ul> <li>Recognition of antigens presented by MHC molecules (MHC 1 and MHC 2)</li> <li>Facilitate communication between T-cells and antigen-presenting cells (APCs)</li> <li>CD4 binds to MHC 2, CD8 binds to MHC 1</li> </ul> </ul> <li>T-cell maturation</li> <ul> <li>Clonal selection outside thymus: Mature T-cells that have undergone positive and negative selection in the thymus migrate to peripheral tissues</li> <li>Binding to antigen fragments: T-cell receptors (TCRs) on T-cells recognize and bind to specific antigen fragments presented by Antigen-Presenting Cells (APCs)</li> </ul> <li>Helper T-cells role</li> <ul> <li>Activated by immune cells with MHC 2</li> <li>Release lymphokines for signaling</li> </ul> <li>Cytotoxic T-cells role</li> <ul> <li>Destroy infected body cells</li> <li>Scan for MHC 1 displaying foreign antigen</li> </ul> <li>Memory T-cells role</li> <ul> <li>Remember past pathogens</li> <li>Rapid response for secondary infections</li> </ul> <li>Regulatory T-cells role</li> <ul> <li>Suppress immune responses</li> <li>Maintain self-tolerance</li> </ul> <li>HIV and helper T-cells</li> <ul> <li>HIV destroys helper T-cells</li> <li>AIDS develops with significant loss of helper T-cells</li> </ul>

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What is the difference between cell-mediated immunity and humoral immunity?

Cell-mediated immunity is a component of the adaptive immune system, a defense mechanism that provides specific and long-lasting protection against pathogens through the recognition and targeting of specific antigens; specifically, cell-mediated immunity involves the activation of T-cells by antigens presented on the surface of infected cells or abnormal cells, like cancer cells. This leads to the direct destruction of the affected cells. On the other hand, humoral immunity is mediated by B-cells, which produce antibodies that target and neutralize pathogens in the extracellular environment, such as bacteria and viruses. Both cell-mediated and humoral immunity are essential components of the body's immune response.

How do T-cells recognize and respond to antigens during cell-mediated immunity?

T-cells, specifically cytotoxic T-cells, recognize antigens through the interaction with the major histocompatibility complex (MHC) class I molecules present on the surface of all nucleated cells. These MHC molecules display small peptide fragments derived from intracellular pathogens or abnormal proteins. When a cytotoxic T-cell encounters a cell with a foreign peptide-MHC complex, it binds to the complex and initiates a series of events that ultimately lead to the destruction of the affected cell. This targeted response is crucial for combating intracellular infections and eliminating abnormal cells, such as cancer cells.

What role does the thymus play in cell-mediated immunity and the development of T-cells?

The thymus is a primary lymphoid organ where T-cells are generated and undergo maturation before they become fully functional, immunocompetent cells. In the thymus, T-cells undergo a process called thymic selection, which involves testing the ability of T-cells to recognize self-antigens in the context of self-MHC molecules. This process ensures that T-cells are not only able to recognize foreign antigens, but also that they do not attack the body's own cells by mistake. After successful thymic selection, mature T-cells are released into the circulation, where they contribute to the cell-mediated immunity process.

Why is the major histocompatibility complex important in cell-mediated immunity?

The major histocompatibility complex (MHC) plays a crucial role in the presentation of antigens to T-cells during the adaptive immune response. MHC molecules are present on the surface of all nucleated cells, displaying peptide fragments derived from intracellular proteins. These peptide fragments can be derived from pathogens, such as viruses, or from abnormal proteins, as in the case of cancer cells. T-cells recognize the peptide-MHC complexes, thus MHC molecules act like a "flag" that allows T-cells to efficiently scan and identify infected or abnormal cells. This recognition is essential for initiating the cell-mediated immune response and eliminating affected cells.

How do B-cells and antibodies contribute to the immune response, and what is their relation to cell-mediated immunity?

B-cells are part of the adaptive immune system and are responsible for the production of antibodies during the humoral immune response. Antibodies are specialized proteins that specifically recognize and neutralize foreign antigens, such as those found on the surface of bacteria and viruses. While B-cells and antibodies play a key role in defending the body against extracellular pathogens, they are not directly involved in cell-mediated immunity. However, they work in conjunction with the cell-mediated immune response, orchestrated by T-cells, to provide a comprehensive defense system against a wide range of infections and threats.