Cross-presentation

Cross-presentation is a process in the immune system where certain antigen presenting cells (APCs) capture extracellular proteins, process them, and present them to T cells. This process is crucial for the initiation of immune responses, particularly against tumors and viruses.

Overview

Cross-presentation is unique to certain types of APCs, such as dendritic cells. These cells are capable of presenting extracellular antigens on MHC class I molecules, which are typically reserved for endogenous antigens. This allows the immune system to recognize and respond to a wider range of threats.

Mechanism

The exact mechanism of cross-presentation is still under investigation, but it is known to involve several steps. First, the APC captures the extracellular protein through endocytosis or phagocytosis. The protein is then processed into smaller peptides within the cell. These peptides are loaded onto MHC class I molecules and transported to the cell surface, where they can be recognized by T cells.

Role in Immunity

Cross-presentation plays a crucial role in the immune response to tumors and viruses. By presenting extracellular antigens on MHC class I molecules, APCs can activate cytotoxic T cells, which are capable of killing infected or malignant cells. This process is also important for the development of immunity following vaccination.

Clinical Significance

Understanding the process of cross-presentation could have significant implications for the development of new immunotherapies. For example, enhancing the ability of APCs to cross-present antigens could potentially improve the effectiveness of cancer vaccines.

See Also

• Antigen presenting cell
• Major Histocompatibility Complex
• T cell
• Immune response
• Immunotherapy

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