Cross-presentation

Definition

Cross-presentation is a unique process where certain antigen-presenting cells (APCs) can present exogenous antigens on major histocompatibility complex (MHC) class I molecules to CD8+ T cells. This mechanism allows the immune system to recognize and respond to pathogens that do not infect APCs directly, bridging a crucial gap in the adaptive immune response. By facilitating the activation of CD8+ T cells, cross-presentation plays an essential role in the body's defense against viruses and tumors.

5 Must Know Facts For Your Next Test

1. Cross-presentation occurs primarily in dendritic cells, which are highly effective APCs that can take up extracellular antigens and present them on MHC class I.
2. This process enables the activation of CD8+ T cells even in cases where the pathogen does not directly infect the presenting cell, enhancing the immune system's ability to eliminate threats.
3. Cross-presentation is critical for generating cytotoxic T lymphocyte (CTL) responses against tumors, as it allows for the presentation of tumor-derived antigens.
4. The mechanism involves endosomal processing of antigens, which then enter the cytosol before being loaded onto MHC class I molecules for presentation.
5. Inadequate cross-presentation can lead to impaired immune responses, making it a potential target for immunotherapy strategies aimed at enhancing anti-tumor immunity.

Review Questions

• How does cross-presentation differ from traditional antigen presentation and why is it important for activating CD8+ T cells?
  • Cross-presentation differs from traditional antigen presentation by allowing exogenous antigens, which normally wouldn't activate CD8+ T cells, to be presented on MHC class I molecules. This is essential because it provides a pathway for the immune system to respond to pathogens that don't infect antigen-presenting cells directly. By bridging this gap, cross-presentation ensures a robust activation of CD8+ T cells, crucial for targeting intracellular infections and tumors.
• Discuss the role of dendritic cells in cross-presentation and how this process contributes to adaptive immunity.
  • Dendritic cells play a pivotal role in cross-presentation due to their unique ability to capture extracellular antigens and present them via MHC class I molecules. This allows them to activate CD8+ T cells and elicit strong cytotoxic responses against various pathogens and tumors. By linking innate recognition with adaptive immunity, dendritic cells enhance the body’s ability to fight off infections and malignancies that require precise targeting by CTLs.
• Evaluate the implications of impaired cross-presentation on tumor immunity and potential therapeutic approaches.
  • Impaired cross-presentation can significantly affect tumor immunity by hindering the activation of CD8+ T cells against cancerous cells, leading to reduced anti-tumor responses. Understanding this limitation opens avenues for therapeutic interventions, such as enhancing dendritic cell function or utilizing adjuvants that boost cross-presentation capabilities. These strategies could help reinvigorate the immune response against tumors, making immunotherapy more effective in treating various cancers.

Related terms

Antigen-presenting cells (APCs): Specialized immune cells that capture, process, and present antigens to T cells, playing a key role in initiating the adaptive immune response.

Major Histocompatibility Complex (MHC): A set of molecules displayed on cell surfaces that present peptide fragments to T cells, crucial for immune recognition and response.

CD8+ T cells:

A subtype of T cells that express the CD8 glycoprotein and are primarily responsible for killing infected or cancerous cells.