Cytotoxic T-cells

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Immunology

Summary

Cytotoxic T-cells (CD8+ T-cells) are indispensable pillars of the immune system, tasked with neutralizing virally infected cells, tumor cells, and under certain circumstances, donor graft cells. Identified by their CD8 surface protein, these cells employ cytotoxic granules, notably perforin and granzyme B, in their defensive operations. Perforin creates pores in the target cell membranes, facilitating the entry of granzyme B, which then triggers a series of events culminating in cell apoptosis. Additionally, the Fas pathway provides an alternative apoptosis mechanism, activated when the Fas ligand on cytotoxic T-cells interacts with the target cell's Fas receptor. Activation is a prerequisite for cytotoxic T-cells to unleash their full potential. This is initiated when the CD8 T-cell receptor identifies and binds to an antigen, presented via MHC class I molecules on affected cells. A secondary confirmation of this foreign presence is achieved through the co-stimulatory interaction between CD28 on cytotoxic T-cells and B7 on antigen-presenting cells. Subsequent to this intensified activation, Th1 helper T-cells release the cytokine IL-2. This cytokine is instrumental in driving the clonal expansion of activated cytotoxic T-cells, ensuring a robust contingent is present at the infection site, primed to neutralize the identified threat.

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FAQs

What role does the Innate Immune System play in responding to viruses?

The Innate Immune System is the first line of defense against viruses. It is activated immediately upon infection, and utilizes various mechanisms such as the complement system and pattern recognition receptors. These receptors detect viral components and trigger signaling pathways to produce antiviral enzymes. This response aims to destroy the virus, limit its replication, and alert the other parts of the immune system about the infection.

How do the Intracellular Defenses of the Innate Immune System work against viruses?

Intracellular defenses form a critical part of the body's response to viruses. When viruses enter human cells, these defenses predominantly include production of interferons and apoptosis. Interferons are proteins that obstruct viral replication within cells, while apoptosis (programmed cell death) is triggered to remove infected cells, thereby limiting the spread of the virus.

What is the role of Interferon Gamma in the Cytotoxic Pathway of the Innate Immune System?

Interferon Gamma, produced by T cells and Natural Killer Cells, helps activate cells involved in the cytotoxic pathway. This pathway targets virally infected cells to destroy them. Interferon Gamma increases MHC 1 expression, vital for presentating viral antigens to immune cells, and activating the cytotoxic response to eliminate the infected cells.

How do Plasmacytoid Dendritic Cells respond to viruses as part of the Innate Immune System?

Plasmacytoid Dendritic Cells are crucial in response to viral infections. Once these cells recognize the presence of a virus through pattern recognition receptors, they produce large amounts of type I interferons. These interferons not only assist in limiting the virus's ability to replicate but also help alert and modulate the adaptive immune response.

What is the difference between Autocrine and Paracrine Signaling in the context of the Innate Immune response to viruses?

Both Autocrine and Paracrine signaling play vital roles in the immune response to viral infections. Autocrine signaling refers to cells responding to substances that they produce themselves. For instance, a cell might produce and respond to interferons in reaction to a viral infection. Paracrine signaling, on the other hand, refers to cells responding to signals from nearby cells. For example, a cell infected by the virus might emit signals that are picked up by neighboring cells, alerting them about the infection.

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