Human Small Intestinal Epithelial Cells Secrete Interleukin-7 and Differentially Express Two Different Interleukin-7 mRNA Transcripts: Implications for Extrathymic T-Cell Differentiation
Introduction
Interleukin-7 (IL-7) is a pleiotropic cytokine, initially described as a growth and differentiation factor for pre-B cells 1, 2and a proliferation factor for mature B cells [3], but has also been shown to have diverse effects on differentiation, growth and function of T cells 4, 5, 6, 7and cells of the myeloid lineage 8, 9. IL-7 supports growth and differentiation of thymocytes through many stages of maturation and is essential for early developmental processes such as the differentiation of pre-T cells into mature thymocytes. This latter function cannot be performed by any other known cytokine [7]. Although IL-7 can promote the differentiation of all T cell phenotypes, it appears to preferentially support the differentiation of pre-T cells into γδ T cell-receptor (TCR)+ 10, 11and CD8+ T cells 10, 12. Effects of IL-7 on mature T cells include upregulation of several activation markers 13, 14, 15, 16, induction of IL-2, IL-4, IL-6 and IFN-γ secretion 13, 17, proliferation 13, 14, 16, and cytotoxic function 18, 19, 20.
Recent evidence has indicated that the small intestine may be a site of extrathymic T cell differentiation. Phenotypic analyses of human intraepithelial lymphocyte (IEL) populations in the small intestine have revealed the presence of a subpopulation of T cells expressing the CD8αβcells and double negative CD4− CD8− T cells 21, 22. Murine studies have suggested that these intestinal T cell populations are of extrathymic origin 23, 24. The expression of the recombinase activation genes RAG1 and RAG2 mRNA in the human small intestinal epithelial layer [25]is a further indication that T cell maturation may be taking place locally.
T cell maturation and differentiation is dependent upon several components provided by other cells, including cytokines and surface molecules that drive the selection of a specific mature T cell repertoire. In the thymus, many of the components are provided by cortical and medullary EC [26]but it is not known if small intestinal EC have an influence on the distinct repertoire of T cells found in the intestinal mucosa. Normal small intestinal, but not colonic, EC express major histocompatibility complex class II molecules 27, 28, 29and CD1 [30]. These cells have been shown to produce IL-6 31, 32and express IL-1 mRNA [32]. Therefore, small intestinal EC are able to generate many of the elements produced by EC in the thymus that have been identified as important for T cell maturation.
An essential requirement for T cell differentiation in the thymus is local IL-7 production by subcapsular and cortical EC [26]; therefore, we have investigated whether human small intestinal EC are capable of producing IL-7 mRNA and protein. IL-7 production by human small intestinal EC would indicate that these cells may influence local T cell activation and that they have the potential to provide an environment suitable for local maturation of immature IEL.
Section snippets
Human Tissue Specimens
Five duodenal biopsies were obtained from each of two consenting patients (individuals 1 and 2) undergoing oesophagogastroduodenoscopy, in whom small intestinal disease was excluded by endoscopic and histological analysis. Surgical specimens of uninvolved ileal tissue were obtained from a further two patients (individuals 3 and 4) undergoing resection for colonic cancer and were dissected to fragments smaller than 1 cm2. Biopsies or surgical specimen fragments were collected in ion-free Hanks’
Detection of IL-7 mRNA
Two DNA fragments were obtained by PCR amplification of reverse transcribed mRNA extracted from bone marrow (Fig. 1) and thymus specimens using the IL-7 primers. These included the predicted 620 bp fragment of IL-7 cDNA (band 1) and a smaller DNA product (band 2), corresponding to a 488 bp fragment produced by alternative IL-7 mRNA splicing [36]. Both bands were expressed in each of the four bone marrow samples (individuals 5–8) and in the thymus (individual 9) used as positive controls for
Discussion
The results of the present study indicate that the human small intestinal epithelial layer produces IL-7. This has been demonstrated both at the level of gene expression and protein secretion. The levels of IL-7 secreted by normal small intestinal epithelial layer specimens are comparable to those secreted by bone marrow cells and PBMC. We also have shown differential expression of two distinct IL-7 transcripts in the epithelial layer. Nucleotide sequence analysis confirmed that the 620 bp PCR
Acknowledgements
We would like to thank Mr. Ken Mealy for providing us with the surgical specimens, Dr. David Noone for performing the automatic sequencing, R&D Systems for performing the IL-7 ’ELISA’ assays and the Irish Health Research Board for financial support.
References (50)
- et al.
A stimulatory effect of recombinant murine interleukin-7 (IL-7) on B-cell colony formation and an inhibitory effect of IL-1 alpha
Blood
(1989) - et al.
Cytokine production and requirements during T-cell development
Curr Op Immunol
(1995) - et al.
Multiple cytokine secretion by IL-7-stimulated human T cells
Cytokine
(1992) - et al.
Interleukin-7 induces differential lymphokine-activated killer cell activity against human melanoma cells, keratinocytes, and endothelial cells
J Invest Dermatol
(1994) - et al.
Flow cytometric analysis of surface major histocompatibility complex class II expression on human epithelial cells prepared from small intestinal biopsies
J Immunol Methods
(1993) - et al.
Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction
Anal Biochem
(1987) - et al.
Extrathymic T cell differentiation
Curr Op Immunol
(1995) - et al.
Stimulation of B-cell progenitors by cloned murine interleukin-7
Nature
(1988) - et al.
Human interleukin 7 is a B cell growth factor for activated B cells
Eur J Immunol
(1991) - et al.
The pleiotropic effects of interleukin 7 and their pathologic and therapeutic implications
Eur J Med
(1992)
Cutaneous lymphoproliferation and lymphomas in interleukin 7 transgenic mice
J Exp Med
The effect of in vivo IL-7 deprivation on T cell maturation
J Exp Med
Interleukin 7 induces cytokine secretion and tumoricidal activity by human peripheral blood monocytes
J Exp Med
The development of T and non-T cell lineages from CD34+ human thymic precursors can be traced by the differential expression of CD44
J Exp Med
Interleukin 7 preferentially supports the growth of gamma delta T cell receptor-bearing T cells from fetal thymocytes in vitro
Int Immunol
Involvement of IL-7 in the development of gamma delta T cells in the thymus
Thymus
Administration of IL-7 to normal mice stimulates B-lymphopoiesis and peripheral lymphadenopathy
J Immunol
Recombinant interleukin 7, pre-B cell growth factor, has costimulatory activity on purified mature T cells
J Exp Med
Human IL-7A novel T cell growth factor
J Immunol
IL-7 induces human lymphokine-activated killer cell activity and is regulated by IL-4
J Immunol
Interleukin-7 is a potent co-stimulus of the adhesion pathway involving CD2 and CD28 molecules
Immunology
Interleukin 7 enhances cytolytic T lymphocyte generation and induces lymphokine-activated killer cells from human peripheral blood
J Exp Med
Use of interleukin-7, interleukin-2, and interferon-gamma to propagate CD4+ T cells in culture with maintained antigen specificity
J Immunother
Subsets of CD3+ (T cell receptor alpha/beta or gamma/delta) and CD3− lymphocytesormal human gut epithelium display phenotypical features different from their counterparts in peripheral blood
Eur J Immunol
Flow cytometric analysis of intraepithelial lymphocytes from human small intestinal biopsies reveals populations of CD4+CD8+ and CD8αα+ cells
Eur J Gastroenterol Hepatol
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