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Human small intestinal mucosa harbours a small population of cytolytically active CD8+ alphabeta T lymphocytes.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Immunology/Immunchemistry.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Immunology/Immunchemistry.
2002 (English)In: Immunology, Vol. 106, no 4, 476-485 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2002. Vol. 106, no 4, 476-485 p.
National Category
Immunology
Identifiers
URN: urn:nbn:se:umu:diva-3291OAI: oai:DiVA.org:umu-3291DiVA: diva2:141834
Available from: 2003-12-18 Created: 2003-12-18 Last updated: 2013-08-06Bibliographically approved
In thesis
1. Extrathymic T cell receptor gene rearrangement in human alimentary tract
Open this publication in new window or tab >>Extrathymic T cell receptor gene rearrangement in human alimentary tract
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

T lymphocytes regulate the initiation, duration, and magnitude of adaptive immune responses and function as effector cells in cell mediated immunity. To become immunologically competent they must generate functional antigen receptors. This process takes place in the thymus and requires somatic recombination of T cell receptor (TCR) genes. It is mediated by the endonucleases recombination activating gene-1 (RAG1) and RAG2. Although the thymus regresses at puberty, T cells are present throughout life implying that other tissues must provide the proper milieu for T cell development. This thesis describes extrathymic T cell maturation in man. RAG1, RAG2, and the preTα-chain (pTα), which is exclusively utilized in developing T cells, were used as markers for TCR gene rearrangement. Two new exons (1A and 1B) encoding sequences in the 5’ untranslated region (5’UTR) of mRNA were discovered in the human RAG1 gene. The previously described 5’UTR exon (renamed 1C) was located between the new exons and exon 2, the latter containing the entire coding sequence. We found that small intestinal lymphocytes of the T cell lineage expressed the new exons in three different splice forms. RAG1 mRNA containing the 1C exon was not expressed in small intestinal lymphocytes. In contrast, splice forms containing the 1A exon were not expressed in thymocytes. RAG1 and pTα mRNA expressing lymphocytes were seen both within the epithelium and in lamina propria. Thymocyte-like CD2+CD7+CD3-, CD4+CD8+, CD1a+, and IL7-R+ lymphocytes were identified in the small intestinal mucosa. CD2+CD7+CD3- cells had the highest expression levels of mRNA for RAG1 and pTα, suggesting that the small intestinal mucosa is indeed a site for T cell maturation. Small intestinal T lymphocytes were also shown to kill via the Fas/FasL pathway in a TCR/CD3 independent manner and via the perforin/granzyme pathway in a TCR/CD3 dependent manner. The Fas/FasL-mediated cytotoxicity may reflect an ongoing selection process of extrathymically maturated T cells.

The nasopharyngeal tonsil is the major inductive site for immune reactions against inhaled antigens. Previous demonstration of RAG1 expression in tonsillar B cells was interpreted as antigen driven receptor revision. The present study confirms the expression of RAG1 in B cells. We also found that RAG1, RAG2, and pTa mRNAs were expressed in lymphocytes of the T cell lineage. A small population of cells with the immature phenotype CD2+CD7+CD3- was demonstrated. This population had the highest expression levels of mRNA for RAG1, RAG2, pTα and terminal deoxynucleotidyl transferase. All four splice-forms of RAG1 mRNA were expressed. RAG1 and pTα mRNA expressing cells were mainly located in the proximity of the surface epithelium and in the outer rim of the follicles. These results suggest that the nasopharyngeal tonsil is a site where extrathymic T cell development and antigen driven TCR revision are occurring in parallel.

Celiac disease (CD) is a small intestinal enteropathy characterized by permanent intolerance to gluten. Gluten reactive intestinal T cells are central in the pathogenesis and CD can be regarded as a failure to maintain tolerance to this food antigen. Expression of the RAG1 1A/2 splice form was significantly decreased in small intestinal T cell subsets of CD patients suggesting that impaired TCR gene rearrangement could contribute to failure of maintain tolerance in CD.

Together, these findings show that both small intestinal and nasopharyngeal tonsillar lymphocytes of T cell lineage have the molecular machinery for antigen receptor rearrangement and that thymocyte-like lymphocytes are present in both tissues. Thus these organs are likely sites of T lymphocyte ontogeny as well as for secondary T cell receptor rearrangement in man.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2003. 69 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 856
Keyword
Immunology, T cell maturation, recombination activating gene, preTα, human intestinal mucosa, intraepithelial lymphocytes, lamina propria lymphocytes, nasopharyngeal tonsil, Immunologi
National Category
Immunology in the medical area
Research subject
Immunology
Identifiers
urn:nbn:se:umu:diva-169 (URN)91-7305-524-7 (ISBN)
Public defence
2004-01-16, E04, 6E, Umeå Universitet, Umeå, 09:00
Opponent
Supervisors
Available from: 2003-12-18 Created: 2003-12-18 Last updated: 2013-03-25Bibliographically approved
2. Human intestinal T lymphocytes: a comparative analysis of phenotype and function in normal and inflamed mucosa
Open this publication in new window or tab >>Human intestinal T lymphocytes: a comparative analysis of phenotype and function in normal and inflamed mucosa
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The epithelial lining of the gut must allow immediate contact with beneficial components as nutrients and normal microflora. At the same time it runs the constant risk of attack from pathogenic microbes and noxious agents. Only a singel layer of epithelial cells separates the body's largest lymphocyte population from foreign components in the gut lumen. I have addressed two fundamental questions: 1) How does the immune system in the gut specifically protect against infectious agents and other harmful substances and at the same time avoid overreaction against antigens in food and commensals? and 2) What causes the immune protection breakdown in inflammatory bowel disease? To this end, the phenotype, distribution and functions of T lymphocytes, key players in adaptive immunity, were compared to T lymphocytes in the chronically inflamed intestine of patients with ulcerative colitis (UC) and Crohn's disease (CD). Intestinal T lymphocytes are present both within the epithelium, intraepithelial lymphocytes (IEL), and in the underlying lamina propria (LP). Even though there are many T lymphocytes in normal intestine, there is a highly significant increase in inflamed intestine. They seem to be involved in the pathogenesis of both UC and CD. In UC, T lymphocytes populate the basal lymphoid aggregates, which occupy up to 45% of LP.

Phenotype was analysed in situ by immunomorphometry and immunoelecton microscopy, and by immunoflow cytometry of isolated IEL and lamina propria lymphocytes (LPL). Cytokine production was monitored as the frequencies of cells expressing the proteins in situ and as mRNA expression in purified T lymphocytes using quantitative RT-PCR. Cytotoxicity was measured in functional assays using purified IEL and LPL as effector cells and as expression of cytotoxic effector molecules. The responsiveness to polyclonal T cell activators was assayed as proliferation and secretion of cytokines in vitro.

Major findings were: (1) Interleukin-2 (IL-2), the Th1 cytokines interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), the down-regulatory cytokine transforming growth factor-β1 (TGF-β1) and the chemokine IL-8 are normally produced by IEL and LPL in both small and large intestine. Activation in vitro enhanced IFN-γ and TGF-β1 production and induced IL-10. These data indicate ongoing controlled cell mediated immune activity and readiness for both pro-inflammatory and immunosuppressive responses. (2) IEL and LPL of both small and large intestine exhibited a capacity to kill via the Fas/FasL pathway in a T cell antigen receptor (TCR)/CD3 independent manner. FasL expressing cells were present both intraepithelially and in LP and were most abundant in LP of colon, where they constitute 30% of the immune cells. These results suggest that local immune activity in the intestinal mucosa is controlled by activation induced cell death, AICD. Small intestinal mucosa harbours a small population of CD8+ αβ+T lymphocytes with cytolytic machinery that can be triggered through the TCR/CD3 complex. These T cells use the perforin/granzyme exocytosis pathway for killing. Such cells are not detected in colon. Most probably these cytotoxic T lymphocytes are "caught in the act" of eliminating virus infected epithelial cells. (3) Inflammation in colon leads to activation of γδ T cells. In UC, Vδ1+ γδ T cells, which normally reside within the epithelium, were numerous in LP. They constituted as much as 15% of the cells in the lymphoid aggregates and showed TCR-γδ internalisation and surface down-regulation, signs of receptor mediated activation. Thus, γδ T cells appear to be recruited from the epithelium in response to nominal antigens present in LP. (4) The cytokine profile of LP T cells was markedly distorted in UC patients and regulatory T cells were induced. IL-10 production was increased and expression levels correlated with disease activity while TGF-β1 levels were unchanged. CD4+ T cells were the major source of IL-10. Moreover, cells with the regulatory/suppressor phenotype CD4+CD28-TCR-αβ+ were frequent, particularly in the aggregates. IL-2 production was shut off and production of IFN-γ and TNF-α was decreased. However, we found no evidence for a corresponding induction of the Th2 cytokines. (5) There was a parallel accumulation of FasL expressing cells with retained capacity to kill via the Fas/FasL pathway and apoptosis resistant bcl-2 expressing lymphocytes in UC. Inflammation in ileum of CD patients led to an enhanced cytotoxicity. The frequency of perforin expressing LPL was increased and the capacity of LPL to execute TCR/CD3 mediated cytotoxicity via the perforin exocytosis pathway was elevated.

In summary, it appears that intestinal T lymphocytes are constantly involved in cell mediated immune activities and that cytotoxic memory CD8+ αβ T cells accumulate in the small intestinal mucosa. IEL and LPL seem capable of down-regulatory actions in the context of proinflammatory cytokines and the local homeostasis of immune reactions to luminal components seems to be regulated by IL-2 dependent AICD. The cytokine profile in UC suggests a generalised activation of regulatory T cells along the intestine. Inflammation in colon, but not in ileum, point to the importance of colonic microflora for precipitating the proinflammatory actions of IL-10.

 

 

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2002. 70 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 769
Keyword
human intestinal mucosa, intraepithelial lymphocyte, lamina propria lymphocyte, γδ T cell, regulatory T cell, cytotoxicity, cytokine, basal lymphoid aggregate, ulcerative colitis, Crohn's disease
National Category
Immunology in the medical area
Identifiers
urn:nbn:se:umu:diva-79076 (URN)91-7305-165-9 (ISBN)
Public defence
2002-01-19, Astrid Fagraeussalen (A103), Norrlands universitetssjukhus, Umeå, 10:00
Opponent
Available from: 2013-08-06 Created: 2013-08-06 Last updated: 2013-08-06Bibliographically approved

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