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Why is Antigen Presentation Critical for the Activation of T Cells?

Antigen presentation is a key process that helps activate T cells, which are a vital part of our immune system.

This process shows tiny pieces of proteins from germs on special molecules called Major Histocompatibility Complex (MHC) molecules. This allows T cells to identify and respond to infected or unusual cells.

Importance of MHC Molecules

  1. Types of MHC:

    • MHC Class I: Found on almost all cells that have a nucleus. They show pieces of proteins from inside the cell. T cells that recognize these pieces are called CD8+ cytotoxic T lymphocytes (CTLs).
    • MHC Class II: Mostly found on special cells called antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells. These molecules show pieces of proteins that come from outside the cell to CD4+ helper T cells.

  2. Diversity and Specificity:

    • There are over 20,000 different types of MHC class I molecules in people. This variety helps our immune systems recognize many different germs. The differences in MHC molecules among people help create a strong immune response in the population.

How Antigen Presentation Works

  • Processing of Antigens:

    • Inside the cell, proteins are broken down into smaller pieces by a machine called the proteasome. These pieces are then moved to the endoplasmic reticulum and attached to MHC class I molecules.
    • For proteins from outside the cell, APCs take them in, break them down in special compartments, and then put the pieces on MHC class II molecules.

  • T Cell Activation:

    • T cells need two signals to be activated:
      • Signal 1: The T cell receptor (TCR) recognizes the peptide-MHC complex. This interaction is very strong.
      • Signal 2: T cells also need help from APCs. This includes other molecules like CD80/CD86 on APCs interacting with CD28 on T cells.

Facts About T Cell Activation

  • About 1 in 10,000 naive T cells in the body can recognize a specific germ because of the great variety of TCRs.
  • To activate one naive T cell, at least 3 different antigen-presenting cells usually need to be involved.
  • When antigen presentation works well, one activated T cell can multiply and create over 1,000 new T cells in just a week.

In short, antigen presentation is very important for activating T cells. It helps target germs specifically and plays a major role in our immune response.

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Why is Antigen Presentation Critical for the Activation of T Cells?

Antigen presentation is a key process that helps activate T cells, which are a vital part of our immune system.

This process shows tiny pieces of proteins from germs on special molecules called Major Histocompatibility Complex (MHC) molecules. This allows T cells to identify and respond to infected or unusual cells.

Importance of MHC Molecules

  1. Types of MHC:

    • MHC Class I: Found on almost all cells that have a nucleus. They show pieces of proteins from inside the cell. T cells that recognize these pieces are called CD8+ cytotoxic T lymphocytes (CTLs).
    • MHC Class II: Mostly found on special cells called antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells. These molecules show pieces of proteins that come from outside the cell to CD4+ helper T cells.

  2. Diversity and Specificity:

    • There are over 20,000 different types of MHC class I molecules in people. This variety helps our immune systems recognize many different germs. The differences in MHC molecules among people help create a strong immune response in the population.

How Antigen Presentation Works

  • Processing of Antigens:

    • Inside the cell, proteins are broken down into smaller pieces by a machine called the proteasome. These pieces are then moved to the endoplasmic reticulum and attached to MHC class I molecules.
    • For proteins from outside the cell, APCs take them in, break them down in special compartments, and then put the pieces on MHC class II molecules.

  • T Cell Activation:

    • T cells need two signals to be activated:
      • Signal 1: The T cell receptor (TCR) recognizes the peptide-MHC complex. This interaction is very strong.
      • Signal 2: T cells also need help from APCs. This includes other molecules like CD80/CD86 on APCs interacting with CD28 on T cells.

Facts About T Cell Activation

  • About 1 in 10,000 naive T cells in the body can recognize a specific germ because of the great variety of TCRs.
  • To activate one naive T cell, at least 3 different antigen-presenting cells usually need to be involved.
  • When antigen presentation works well, one activated T cell can multiply and create over 1,000 new T cells in just a week.

In short, antigen presentation is very important for activating T cells. It helps target germs specifically and plays a major role in our immune response.

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