dendritic cell antigen processing and presentation

Definition

Target type: biologicalprocess

The process in which a dendritic cell expresses antigen (peptide or lipid) on its cell surface in association with an MHC protein complex. [GOC:add, ISBN:0781735149, PMID:15771591]

Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) that play a crucial role in initiating and shaping adaptive immune responses. They excel at capturing antigens from the environment, processing them into immunogenic peptides, and presenting these peptides to T cells, thereby triggering T cell activation and differentiation. The process of antigen processing and presentation by DCs involves several key steps:

1. **Antigen Uptake:** DCs possess a variety of receptors and mechanisms for capturing antigens from their surroundings. These include:
* **Phagocytosis:** DCs engulf large particles, such as bacteria, viruses, and apoptotic cells, using their pseudopodia.
* **Macropinocytosis:** DCs take up fluid and dissolved substances through large, non-specific vesicles.
* **Receptor-mediated endocytosis:** DCs use specific receptors, such as Toll-like receptors (TLRs) and C-type lectin receptors (CLRs), to internalize antigens bound to these receptors.
2. **Antigen Processing:** Once internalized, antigens are processed within DCs into smaller peptides that can be presented to T cells. This processing involves two major pathways:
* **Endocytic pathway:** This pathway is primarily used for processing exogenous antigens, such as those derived from bacteria or viruses. Antigens are internalized into endocytic vesicles, where they are degraded by lysosomal enzymes, including proteases and cathepsins. The resulting peptides are loaded onto MHC class II molecules.
* **Cytosolic pathway:** This pathway processes endogenous antigens, such as those derived from viral proteins synthesized within the cell. Antigens are degraded by proteasomes into small peptides, which are then transported into the endoplasmic reticulum (ER) by the transporter associated with antigen processing (TAP). In the ER, peptides are loaded onto MHC class I molecules.
3. **MHC Presentation:** Processed peptides are loaded onto MHC molecules, which are specialized cell surface proteins that act as antigen presenters. There are two main classes of MHC molecules:
* **MHC class I:** These molecules present peptides derived from the cytosolic pathway to CD8+ cytotoxic T cells.
* **MHC class II:** These molecules present peptides derived from the endocytic pathway to CD4+ helper T cells.
4. **T Cell Activation:** DCs migrate from peripheral tissues to lymph nodes, where they interact with naive T cells. The interaction between MHC molecules on DCs and T cell receptors (TCRs) on T cells triggers the activation of T cells.
* **MHC class I-peptide-TCR interaction:** Activates CD8+ cytotoxic T cells, which differentiate into effector T cells capable of killing infected or cancerous cells.
* **MHC class II-peptide-TCR interaction:** Activates CD4+ helper T cells, which differentiate into various subsets, including Th1 cells, Th2 cells, and Th17 cells, each contributing to different aspects of the immune response.

The process of antigen processing and presentation by DCs is highly regulated and involves a complex interplay of intracellular pathways and signaling events. DCs are critically important for initiating and shaping adaptive immune responses, as they bridge the gap between innate and adaptive immunity and play a pivotal role in immunity against pathogens, tumor surveillance, and maintaining immune tolerance.'"

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Compounds (4)