CD8+

CD8+

CD8+ refers to a type of T cell that plays a crucial role in the immune system. These cells are characterized by the presence of the CD8 glycoprotein on their surface, which acts as a co-receptor that enhances the ability of T cells to recognize antigens presented by MHC class I molecules. CD8+ T cells are primarily involved in the direct killing of infected or cancerous cells.

Function

CD8+ T cells, also known as cytotoxic T lymphocytes (CTLs), are essential for the adaptive immune response. They are responsible for:

• Recognizing and eliminating infected cells: CD8+ T cells can detect cells that have been infected by viruses or other intracellular pathogens. They recognize antigens presented by MHC class I molecules on the surface of these infected cells.

• Killing cancerous cells: CD8+ T cells can also target and destroy tumor cells that present abnormal antigens.

• Releasing cytotoxic granules: Upon recognition of a target cell, CD8+ T cells release perforin and granzymes, which induce apoptosis in the target cell.

• Producing cytokines: CD8+ T cells secrete cytokines such as interferon gamma (IFN-γ), which have antiviral and immunomodulatory effects.

Development

CD8+ T cells develop in the thymus from precursor cells. During their development, they undergo a selection process to ensure that they can effectively recognize foreign antigens while being tolerant to self-antigens. This process involves:

• Positive selection: Ensures that T cells can recognize self-MHC molecules.
• Negative selection: Eliminates T cells that strongly react to self-antigens.

Activation

CD8+ T cells require two signals for activation:

1. Antigen recognition: The T cell receptor (TCR) on CD8+ T cells binds to a specific antigen presented by MHC class I molecules on the surface of an antigen-presenting cell (APC). 2. Co-stimulation: Additional signals provided by co-stimulatory molecules on the APC, such as CD28 binding to B7.

Once activated, CD8+ T cells proliferate and differentiate into effector cells capable of killing target cells.

Clinical Significance

CD8+ T cells are critical in the control of viral infections and cancer. However, their activity can also contribute to autoimmune diseases and transplant rejection. Understanding the regulation of CD8+ T cell responses is important for developing therapies for infectious diseases, cancer, and autoimmune conditions.

Also see

• CD4+ T cell
• Major histocompatibility complex
• Adaptive immune system
• Cytokine