Lymphocytes: Intraepithelial

Hilde Cheroutre, La Jolla Institute for Allergy and Immunology, San Diego, California, USA
Florence Lambolez, La Jolla Institute for Allergy and Immunology, San Diego, California, USA

Published online: March 2009

DOI: 10.1002/9780470015902.a0001197.pub2

Intraepithelial lymphocytes (IEL) are small, round mononuclear immune cells, which reside in the paracellular space between nonimmune epithelial cells. They are found in the skin and within the epithelial layer that lines the intestine, the biliary tract, the oral cavity, the upper respiratory tract and lungs and the reproductive tract. The largest population of IEL resides within the epithelium of the small intestine where they form the first line of immune defence against invading pathogens while preserving the integrity of the mucosal barrier.

Key concepts

  • The lymphocytes located in the epithelium are at the frontline between the self and nonself.
  • The T-cell populations from the small intestine are the most important in number and the most diverse in the body.
  • The T-cell populations from the epithelium often contain unconventional subpopulation such as CD8aa TCRab+ IEL in the intestine.
  • Introduction of the new concept of agonist selection for self-specific CD8aa TCRab+ IEL.
  • Important function of IEL during immune response against pathogens.

Keywords: ; T cell; ; T cell; CD8; cytotoxic T cell; cytokine; agonist selection

Figure 1. (a) Villi architecture of the small intestinal epithelium in mouse. Hematoxyline-Eosin staining. (b) T cells in the villi of normal human small intestine. Note the high density of T cells (intraepithelial lymphocytes) are basolaterally situated in the epithelial layer. Immunoperoxidase with anti-CD3, original magnification ×100.
Figure 2. Schema summarizing the differentiation of type a and b IEL. CD4 and CD8 TCRab differentiate in the thymus through a CD4+ CD8+ (DP) stage. CD4 and CD8+ mature T cells leave the thymus to colonize peripheral lymphoid tissue where they stay as naïve T cells. Under antigenic stimulation they will differentiate into effector T cells and gain the capacity to migrate to the intestinal epithelium. CD8 TCR differentiate in the thymus through the CD4 CD8 CD8 (TP) stage and later CD4– CD8– (DN) TCR+. DN TCR+ egress the thymus and reach the small intestine epithelium where they express CD8 under IL-15 to become CD8 TCR IEL. Finally CD8 TCR IEL develop from CD4– CD8– (DN) precursors.
Figure 3. Schematic representation of the recognition elements of TCR IEL cells on the surface of normal and infected epithelial cells. Normal epithelial cells in the small intestine express low level of MICA and MICB. The expression of these molecules is upregulated during inflammation and/or infections by a heat shock response element promoter. When high levels of MICA or MICB are expressed, TCR is engaged and the T cell kills the epithelial cell. This mechanism must be efficient for the elimination of infected epithelial cells.
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Article Title: Lymphocytes: Intraepithelial
 
How to Cite close
Cheroutre, Hilde, and Lambolez, Florence(Mar 2009) Lymphocytes: Intraepithelial. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001197.pub2]