There are 3 main types of T cells: cytotoxic, helper, and regulatory. Each of them has a different role in the immune response.
Cytotoxic T cells (CD8+)
Cytotoxic T cells (Tc cells) have a co-receptor called CD8 on their cell surface. CD8 partners with the T cell receptor and with MHC class I molecules, acting as a sort of bridge. This bridge allows cytotoxic T cells to recognize normal cells that are infected by a pathogen. When the cytotoxic T cell recognizes the infected cell, it becomes activated and produces molecules that kill the infected cell, destroying the pathogen in the process.
Helper T cells (CD4+)
Helper T cells (Th cells) have a different co-receptor called CD4 on their cell surface. CD4 also partners with the T cell receptor but interacts with MHC class II molecules instead of MHC class I molecules. This allows helper T cells to recognize pathogen peptides that have been displayed by antigen presenting cells. When helper T cells recognize a peptide on an antigen presenting cell, they become activated and begin to produce molecules called cytokines that signal to other immune cells.
There are many subtypes of helper T cells (ie, Th1, Th2, Th17). Each subtype produces a specialized combination of cytokines that depends on type of pathogen that the helper T cell has recognized—some cytokines are more effective than others in the process of eliminating certain invaders.
Regulatory T cells
Regulatory T cells (Treg cells) also have CD4 on their surface, but they do not activate the immune system like helper T cells do. Instead, regulatory T cells play a protective role by shutting off the immune response when it is no longer needed. This prevents excessive damage to the normal cells and tissues in the body. Regulatory T cells suppress the immune response in several ways, including:
- Producing anti-inflammatory cytokines that suppress the immune response
- Releasing molecules that kill activated immune cells
- Changing the way dendritic cells behave so they can't activate T cells
Which T cells are involved in celiac disease?
Of the 3 types of T cells described above, the CD4+ T helper cells play a leading role in celiac disease. These are the cells that mistakenly recognize gluten as a pathogen and trigger an immune response (see below).1 However, cytotoxic CD8+ T cells known as intraepithelial lymphocytes (IELs) are also important as they are drivers of tissue damage in the intestine.2
- Jabri B, Sollid LM. T Cells in Celiac Disease. J Immunol. 2017;198(8):3005-3014.
- Abadie V, Discepolo V, Jabri B. Intraepithelial lymphocytes in celiac disease immunopathology. Semin Immunopathol. 2012;34(4):551-566.
Antibodies - Y-shaped proteins that recognize foreign pathogens. Made by B cells. Also called immunoglobulins.
Antigen presenting cell - A specialized immune cell that presents peptides to CD4+ or CD8+ T cells. Peptides are presented by MHC I or MHC II proteins.
CD4 - A co-receptor on the surface of helper T cells.
CD8 - A co-receptor on the surface of cytotoxic T cells.
Cytokines - Small proteins that are made and released by immune cells. Allows cells to send signals and provide instructions to other cells.
Cytotoxic T cell - Adaptive CD8+ immune cell that kill infected cells when activated.
Dendritic cell - A type of antigen presenting cell that processes pathogens and foreign proteins. Presents peptides to T cells.
Helper T cell - Adaptive CD4+ immune cell that produces cytokines when activated.
Immune cells - Specialized white blood cells (also called leukocytes) that fight infection.
Intraepithelial lymphocytes - Cytotoxic CD8+ T cells that reside in the intestine. Contribute to tissue damage in celiac disease.
MHC class I protein - Major histocompatibility complex class I protein. Found on the surface of normal cells. Presents peptides to CD8+ T cells.
MHC class II protein - Major histocompatibility complex class II protein. Found on the surface of antigen presenting cells. Presents peptides to CD4+ T cells.
Pathogens - Bacteria and viruses that can cause disease.
Peptide - A small protein fragment consisting of a chain of amino acids.
Receptor - A protein that is located on the surface of a cell and interacts with other proteins. Receptors act as the “locks” that recognize specific pathogen “keys”.
Regulatory T cell - An adaptive immune cell that suppresses the immune response.
T cell - A type of adaptive immune cell. Also called T lymphocyte.
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