CD8+ T cells

Cell biology

CD8+ T cells, also known as CD8-positive T cells or cytotoxic T cells, are a type of T cell that play a crucial role in the immune system to fight against pathogens and cancer cells. These cells are characterized by the presence of the CD8 glycoprotein on their surface, which primarily binds to Class I MHC molecules on antigen-presenting cells.

Function

CD8+ T cells are primarily involved in the cytotoxic immune response. Upon activation, they can directly kill infected or malignant cells. This is achieved through the release of cytotoxic granules that contain enzymes such as granzymes and perforin, which induce apoptosis in the target cell. Additionally, CD8+ T cells can also produce various cytokines like tumor necrosis factor and interferon-gamma, which help in controlling infections.

Activation

The activation of CD8+ T cells requires the recognition of a specific peptide presented by Class I MHC molecules on the surface of antigen-presenting cells. This interaction is stabilized by the CD8 receptor. Furthermore, additional signals from co-stimulatory molecules and cytokines are necessary to fully activate the CD8+ T cell. Once activated, these cells proliferate and differentiate into effector cytotoxic T cells that can seek out and destroy target cells bearing the antigen.

Regulation

The activity of CD8+ T cells is tightly regulated to prevent excessive immune responses and autoimmunity. Regulatory mechanisms include the expression of inhibitory receptors such as PD-1 and CTLA-4, which can dampen the T cell response when engaged. Additionally, regulatory T cells (Tregs) can suppress the activity of CD8+ T cells through various mechanisms.

Clinical Significance

CD8+ T cells are crucial in the defense against viral infections and in the immune surveillance of tumors. Their role is exploited in various therapeutic strategies, such as cancer immunotherapy, where enhancing the activity of CD8+ T cells can lead to better control of cancer. Conversely, in diseases like AIDS, CD8+ T cells are critical in controlling the spread of HIV, but their function can be impaired as the disease progresses.

Research

Research on CD8+ T cells continues to be a vibrant field, focusing on understanding their biology, enhancing their therapeutic potential, and controlling their activity in autoimmune diseases. Techniques such as gene editing and the use of checkpoint inhibitors are at the forefront of this research, aiming to harness the power of CD8+ T cells more effectively.

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