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11.3K: Intraepithelial T-lymphocytes and B-1 cells

Skills to Develop

  1. Briefly describe how intraepithelial T-lymphocytes (gamma:delta T-lymphocytes) play a role in innate immunity.
  2. Briefly describe how B-1 cells play a role in innate immunity.

We will now take a closer look at Intraepithelial T-lymphocytes (e.g., T4 and T8) and B-1 cells. Most of the T-lymphocytes and B-lymphocytes in the body are involved in the adaptive immune responses that will be discussed in Unit 6. In adaptive immunity, specific receptors on T-lymphocytes (T-cell receptors or TCRs) and B-lymphocytes (B-cell receptors or BCRs) recognize specific antigens of specific microbes.

Intraepithelial T-lymphocytes and B-1 cells, on the other hand, are subpopulations of T-lymphocytes and B-lymphocytes that possess a more limited diversity of receptors and are designed to directly recognize the more common microbes that enter the epidermis or the mucosal epithelia. As such, they function more as effector cells for innate immunity rather than adaptive immunity.

  1. Intraepithelial T-lymphocytes (IELs) are found in the epidermis of the skin and the mucosal epithelia. These T-lymphocytes, known as gamma:delta T-lymphocytes, differ from the T-lymphocytes (alpha:beta T-lymphocytes) associated with adaptive immunity. The alpha:beta T-lymphocytes are designed to recognize peptide antigens bound to MHC-I molecules of infected cells and tumor cells.

    Although their exact function is unknown, it has been proposed that they recognize molecules associated with epithelial cells but expressed only when those cells are infected, such as MHC-I molecules and heat shock proteins. They then trigger apoptosis of these stressed or infected cells using perforins and granzymes similar to cytotoxic T-lymphocytes (CTLs) of adaptive immunity. Rather than recognizing antigens specific to an infectious microorganism, they recognize molecules associated with the epithelium as a consequence of infection. Their T-cell receptors may also function as PRRs for recognizing certain PAMPs. As such, they function more as effector cells for innate immunity rather than adaptive immunity. They probably help defend the body by producing cytokines that play a variety of roles in body defense. IELs are also thought to aid in repair of mucous membranes following inflammatory damage. Excessive or inappropriate activation of IELs can also lead to damage of the intestines as in the case of celiac disease.

  2. B-1 lymphocytes, or B-1 cells are found mostly in the peritoneal and pleural cavities . B-1 cells have a limited diversity of antigen receptors that initially produce a class of antibody molecule called IgM against common polysaccharide and lipid antigens of microbes and against PAMPs. As such they function more as effector cells for innate immunity rather than adaptive immunity. Antibodies produced by B-1 cells are often called natural antibodies that help to protect against bacteria in body cavities. Similar B-lymphocytes called marginal zone B cells are found in the marginal zone of the white pulp of the spleen. These are thought to make IgM to protect against bacteria that enter the bloodstream.

Summary

  1. Most of the T-lymphocytes and B-lymphocytes in the body are involved in the adaptive immune responses wherein specific receptors on T-lymphocytes (T-cell receptors or TCRs) and B-lymphocytes (B-cell receptors or BCRs) recognize specific antigens of specific microbes.
  2. Intraepithelial T-lymphocytes and B-1 cells, however, are subpopulations of T-lymphocytes and B-lymphocytes that possess a more limited diversity of receptors and are designed to directly recognize the more common microbes that enter the epidermis or the mucosal epithelia and function more as effector cells for innate immunity rather than adaptive immunity.
  3. Intraepithelial T-lymphocytes (IELs) are found in the epidermis of the skin and the mucosal epithelia.
  4. It has been proposed that they recognize molecules such as MHC-I molecules and heat shock proteins associated with epithelial cells but expressed only when those cells are infected and trigger apoptosis of these stressed or infected cells. They may also aid in repair of mucous membranes following inflammatory damage.
  5. B-1 lymphocytes, or B-1 cells, are found mostly in the peritoneal and pleural cavities.
  6. B-1 cells have a limited diversity of antigen receptors that initially produce a class of antibody molecule called IgM against common polysaccharide and lipid antigens of microbes and against PAMPs.
  7. Similar B-lymphocytes called marginal zone B cells are found in the spleen.\ and are thought to make IgM to protect against bacteria that enter the bloodstream.

Contributors

  • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)