Antigen processing

Definition

Antigen processing is the biological mechanism by which proteins from pathogens or foreign substances are broken down into smaller peptides that can be presented on the surface of antigen-presenting cells. This process is essential for T cells to recognize and respond to these antigens, ultimately leading to an immune response. Efficient antigen processing is crucial for ensuring that T cells can distinguish between self and non-self, contributing to the activation and differentiation of T cells in the immune system.

5 Must Know Facts For Your Next Test

1. Antigen processing can occur via two main pathways: the endogenous pathway for intracellular proteins and the exogenous pathway for extracellular proteins.
2. During antigen processing, proteins are typically degraded by proteolytic enzymes into peptides ranging from 8 to 20 amino acids in length.
3. MHC class I molecules present processed endogenous antigens to CD8+ cytotoxic T cells, while MHC class II molecules present exogenous antigens to CD4+ helper T cells.
4. The efficiency of antigen processing and presentation can significantly influence the strength of the T cell response against a pathogen.
5. Some pathogens have evolved mechanisms to evade antigen processing and presentation, allowing them to persist and replicate within the host.

Review Questions

• How do different pathways of antigen processing affect T cell responses?
  • Antigen processing involves both endogenous and exogenous pathways, which lead to different outcomes in T cell activation. The endogenous pathway processes intracellular proteins and presents them on MHC class I molecules to CD8+ cytotoxic T cells, enabling these cells to eliminate infected or malignant cells. In contrast, the exogenous pathway involves processing extracellular proteins for MHC class II presentation to CD4+ helper T cells, which support other immune responses like B cell activation. Understanding these pathways helps explain how various types of T cells are activated based on the nature of the antigen.
• Discuss the role of MHC molecules in antigen processing and their importance in activating T cells.
  • MHC molecules play a crucial role in antigen processing by presenting processed peptide fragments on the surface of antigen-presenting cells. MHC class I molecules present peptides derived from endogenous antigens to CD8+ T cells, which are vital for targeting infected or cancerous cells. On the other hand, MHC class II molecules present exogenous antigens to CD4+ helper T cells, initiating a broader immune response. The interaction between MHC molecules and T cell receptors is fundamental for effective T cell activation, highlighting the importance of antigen processing in eliciting a robust immune response.
• Evaluate how pathogens can influence antigen processing and what implications this has for vaccine development.
  • Pathogens can manipulate antigen processing through various strategies, such as producing proteins that interfere with MHC loading or altering the host's proteolytic enzymes. This ability to evade detection poses challenges for effective immune responses and has direct implications for vaccine development. Vaccines must be designed to enhance antigen processing and presentation mechanisms to ensure that T cells can effectively recognize and respond to these pathogens. Understanding these interactions helps researchers create more effective vaccines that can overcome pathogen evasion tactics and induce robust immunity.

Related terms

Major Histocompatibility Complex (MHC): A set of cell surface proteins essential for the immune system to recognize foreign molecules, MHC molecules present processed antigens to T cells.

T cell receptor (TCR):

A molecule found on the surface of T cells that recognizes specific antigens presented by MHC molecules, triggering T cell activation.

Endosomal Processing: A specific type of antigen processing that occurs within endosomes, where extracellular proteins are degraded and loaded onto MHC class II molecules for presentation to CD4+ T cells.