Distribution of beta 7 integrins in human intestinal mucosa and organized gut-associated lymphoid tissue.

Two alternative integrins involved in mucosal homing (alpha 4 beta 7) or epithelial retention (alpha E beta 7) of lymphocytes were examined in the human gut. The distribution of the beta 7 subunit [monoclonal antibody (mAb) M301] was bimodal in that it was strongly expressed by alpha E beta 7 + cells but weakly by alpha 4 beta 7 + cells. More than 90% of intraepithelial lymphocytes (IEL), including the minor subsets of CD4+, T-cell receptor (TCR) gamma/delta +, and CD3- cells, expressed alpha E beta 7 as did most lamina propria CD8+ (88%) and a fraction (36%) of CD4+ lymphocytes. Conversely, B-lineage cells (CD19+) and macrophages (CD68+) were negative. In gut-associated lymphoid tissue (GALT: Peyer's patches and appendix) only a few (< 5%) cells were positive for alpha E beta 7 (confined to CD8+ lymphocytes and CD11c+ putative dendritic cells). A relatively small fraction of IEL (30-50%) expressed alpha 4 beta 7 (mAb Act-1), while most (70%) lamina propria T and B lymphocytes, blasts, plasma cells and macrophages were positive. In GALT, T lymphocytes expressed similar levels of alpha 4 beta 7 as in the lamina propria whereas relatively few B lymphocytes (< 50%) were positive. Isolated lamina propria CD8+, CD4+, CD19+, and CD38+ cells contained mRNA for alpha 4 and the former three subsets as well as appendix CD8+ cells also for beta 7 while only lamina propria CD8+ cells had mRNA for alpha E. Together, the results suggested that alpha E beta 7 and alpha 4 beta 7 are differentially regulated in inductive sites and effector sites of the human gut. Because lymphoid cells at both sites expressed mainly alpha 4 beta 7, this integrin may be a homing receptor on memory and effector cells bound for lamina propria as well as on naive lymphocytes extravasating in GALT. Conversely, because alpha E beta 7 was mainly expressed by CD8+ cells in epithelium and lamina propria, it was probably induced after extravasation, in agreement with the observation that IEL and a fraction of lamina propria T lymphocytes (mainly CD8+ cells) generally expressed higher levels of beta 7 than most CD4+ and B cells. Also a subset of putative dendritic cells located near the follicle-associated epithelium of GALT expressed alpha E beta 7, perhaps reflecting epithelial interaction during primary immune responses.     

Adoptive transfer of T lymphocytes to T-cell-depleted mice inhibits Escherichia coli translocation from the gastrointestinal tract.

Bacterial translocation is defined as the passage of viable bacteria from the gastrointestinal (GI) tract to extraintestinal sites, such as the mesenteric lymph node (MLN), spleen, liver, kidneys, and blood. Previously, we reported that depletion of CD4+ and/or CD8+ T cells promotes bacterial translocation from the GI tract to the MLN. In the present study, CD4+ and/or CD8+ T cells, harvested from donor mice, were adoptively transferred to mice previously depleted of T cells by thymectomy plus intraperitoneal injection of rat anti-mouse T-cell monoclonal antibodies. The adoptively transferred CD4+ and/or CD8+ T cells inhibited the translocation of Escherichia coli from the GI tract. Migration of the adoptively transferred T cells to the spleens and MLNs of the recipient mice was determined by utilizing Thy 1.1+ donor cells adoptively transferred into mice whose cells express the Thy 1.2 marker. These results provide further evidence of the importance of T cells in the host immune defense against bacterial translocation from the GI tract.     

Effects of the lpr/lpr mutation on T and B cell populations in the lamina propria of the small intestine, a mucosal effector site.

MRL mice, which develop a lymphoproliferative disease characterized by increased numbers of alpha/beta T cell receptor+ (TCR+) B220/6B2+CD4-CD8- T cells [lymphoproliferation (lpr) T cells], were studied for the effect of the lpr/lpr mutation on the mucosal immune system in the gastrointestinal (GI) tract. We analyzed the effect of the lpr gene mutation on T and B cell populations in the Peyer's patches (PP) and the lamina propria lymphocytes (LPLs), as examples of major IgA inductive and effector tissues in the GI tract respectively. Normal mouse PP contain B cells committed to IgA (surface IgA+) but only low numbers of B cells producing IgA. However, enhanced spontaneous IgA and IgG synthesis occurs in the PP of MRL mice. Further, we have now shown that PP of MRL mice are populated by lpr T cells. Interestingly, lpr T cells were not present in significant numbers in LPLs of MRL mice, even in older animals. Of interest was the finding that the ratio of CD4+ to CD8+ T cells in the lamina propria was lower in MRL when compared with control mice, and the CD8+ T cell subset actually predominates in LPLs of autoimmune mice. In addition, the number of gamma/delta TCR+ T cells in LPL of MRL lpr/lpr mice was significantly increased, especially in MRL lpr/lpr mice at 6 and 12 weeks of age. When the isotype distribution of B cells in LPLs was analyzed, no changes were noted in MRL lpr/lpr mice in comparison with MRL +/+ or normal control mice, and the pattern was IgA much greater than IgM greater than IgG. These results show that although increased numbers of CD8+ T cells and gamma/delta TCR+ cells occur in the LPLs of MRL mice, a normal distribution of plasma cell isotypes (IgA much greater than IgM greater than IgG) is found in this mucosal compartment. Further, Ipr T cells do not develop in the lamina propria compartment of the GI tract.     

Antigen-specific and polyclonal CD4+ lamina propria T-cell lines: phenotypic and functional characterization.

Surface phenotype and function of lamina propria CD4+ T cells have been evaluated. In addition, long-term, antigen-specific and polyclonal lamina propria CD4+ T-cell lines have been generated and characterized. Lamina propria CD4+ T cells represent approximately 30% of lamina propria lymphocytes and are responsive to a variety of T-cell mitogens, including anti-CD3, concanavalin A, phytohaemagglutinin and pokeweed mitogen. In each case, however, lamina propria T cells are less responsive to these mitogens than spleen T cells. Freshly isolated lamina propria T cells produce substantial amounts of interleukin-2 (IL-2), interleukin-4 (IL-4), gamma interferon and to a lesser extent interleukin-5 (IL-5). Antigen-specific lamina propria CD4+ T-cell lines were generated by orally immunizing animals with antigen (KLH) in conjunction with cholera toxin as an oral adjuvant. Polyclonal lamina propria CD4+ T-cell lines were generated from unimmunized animals using anti-CD3 as a polyclonal stimulus. Both antigen-specific and polyclonal CD4+ T-cell lines were Thy-1+, alpha beta TCR+ and CD8-. The antigen-specific CD4+ T-cell line when stimulated by anti-CD3 and PMA produces predominantly IL-2, IL-4 and gamma interferon, with very little IL-5. In contrast, the polyclonal CD4+ T-cell line when similarly stimulated produces predominantly IL-4 and IL-5, with very little IL-2 and no detectable gamma interferon. In summary, lamina propria CD4+ T cells have been evaluated and in vitro conditions have been determined for successful generation of lamina propria CD4+ T-cell lines.     

Lymphocytes bearing the gamma delta T-cell receptor in normal human intestine and celiac disease

Monoclonal antibodies to T-cell receptors were used to investigate the prevalence of the two distinct T-cell subpopulations (TCR alpha beta+ and TCR gamma delta+ cells) in the intestinal mucosa of children with celiac disease (gluten-sensitive enteropathy) as compared with normal intestinal mucosa. TCR gamma delta+ cells were rarely identified in the epithelium of human fetal or normal postnatal intestine and few were present in the lamina propria, whereas the number of distribution of TCR alpha beta+ cells closely resembled that of CD3+ cells. Compared with normal intestine, a significant increase in the number of CD3+, CD8+, TCR alpha beta+, and TCR gamma delta+ intraepithelial lymphocytes was present in celiac disease. Although the mucosal TCR gamma delta+ cells were less numerous than TCR alpha beta+ cells in celiac disease, there was a marked increase in the number of TCR gamma delta+ cells as compared with controls. The ligand recognized by the gamma delta T-cell receptor and the function of these cells have not been determined; however, these findings suggest a possible role for TCR gamma delta+ lymphocytes in mucosal immune responses and tissue injury as seen in celiac disease.     

Increase in T‐Cell Subsets of Oral Mucosa: a Late Immune Response in Patients with Treated Coeliac Disease?*

BACKGROUND AND AIMS: In coeliac disease, the gut involvement is gluten-dependent. Following the introduction of a gluten-free diet, inflammatory cell infiltration decreases in the small intestinal mucosa. Our hypothesis was that the oral mucosa might mirror the changes found in coeliac disease similarly to the mucosa of the small intestine. Thus, the number of inflammatory cells in the oral mucosa would decrease in patients with coeliac disease on a gluten-free diet. METHODS: The distribution CD45RO+ and CD3(+) T cells, T-cell subpopulations (CD4(+), CD8(+), T-cell receptor (TCR)alpha beta+ and TCR gamma delta+ cells) and HLA DR expression were studied in the buccal mucosa of 15 untreated and 44 gluten-free diet treated coeliac disease patients, and of 19 controls. All 15 patients with untreated coeliac disease were immunglobulin (Ig)A endomysial antibody positive and all 44 patients on gluten-free diet except one were endomysial antibody negative, as were all control subjects. RESULTS: Untreated coeliac disease patients did not differ from controls in the densities of CD45RO+ cells, CD3(+) cells or of T-cell subsets. In contrast, in treated coeliac disease patients, a significant increase in the numbers of mast cells, CD3(+) and CD4(+) lymphocytes was found in the lamina propria of oral mucosa as compared with patients with untreated coeliac disease and controls. The increase in CD3(+) T cells was in part owing to an increase in lymphocytes expressing no TCR. No differences were found in the expression of human leucocyte antigen (HLA) DR in the epithelium or in the lamina propria in the patient groups studied or in the controls. In treated coeliac disease patients only a few TCR gamma delta+ T cells were found intraepithelially and in the lamina propria, but these cells were not detected in the lamina propria of oral mucosa of patients with untreated coeliac disease or in the controls. CONCLUSIONS: The infiltration of T cells into oral mucosa was increased in treated coeliac disease patients in spite of adherence to a gluten-free diet. Because the CD3(+) T cell count was higher than those of the TCR alpha beta+ and TCR gamma delta+ T cells, there must be other cells involved, probably natural killer (NK) cells. The increase in T-cell subsets in the treated coeliac disease patients seems not to result from poor dietary compliance, but might occur as a late immune response in coeliac disease and reflect chronic immunologic stimulation followed by regeneration of memory T cells.     

Development of CD8 alpha/beta + TCR alpha beta intestinal intraepithelial lymphocytes in athymic nu/nu mice and participation in regional immune responses.

On the basis of the CD8 coreceptor expression, T-cell receptor (TCR)alpha beta-bearing intestinal intraepithelial lymphocytes (i-IEL) segregate into two populations. The CD8 alpha alpha + TCR alpha beta i-IEL develop thymus independently, whereas the CD8 alpha beta + TCR alpha beta i-IEL are generally considered to be thymus dependent. Flow cytometry analysis revealed a distinct population of CD8 alpha beta + TCR alpha beta i-IEL in individual athymic nu/nu mice. The i-IEL encompassing CD8 alpha beta + TCR alpha beta cells expressed potent cytolytic and interferon-gamma-producing activities. These findings demonstrate that CD8 alpha beta + TCR alpha beta i-IEL can develop in nu/nu mice independently from a functional thymus and suggest that these cells, directly or indirectly, perform biological functions in the gut.     

MHC class II-independent CD25+ CD4+ CD8alpha beta+ alpha beta T cells attenuate CD4+ T cell-induced transfer colitis

CD4+ alpha beta T cell populations that develop in mice deficient in MHC class II (through 'knockout' of either the Aalpha, or the Abeta chain of the I-A(b) molecule) comprise a major 'single-positive' (SP) CD4+ CD8- subset (60-90%) and a minor 'double-positive' (DP) CD4+ CD8alpha beta+ subset (10-40%). Many DP T cells found in spleen, mesenteric lymph nodes (MLN) and colonic lamina propria (cLP) express CD25, CD103 and Foxp3. Adoptive transfer of SP but not DP T cells from Aalpha(-/-) or Abeta(-/-) B6 mice into congenic RAG(-/-) hosts induces colitis. Transfer of SP T cells repopulates the host with only SP T cells; transfer of DP T cells repopulates the host with DP and SP T cells. Anti-CD25 antibody treatment of mice transplanted with DP T cells induces severe, lethal colitis; anti-CD25 antibody treatment of mice transplanted with SP T cells further aggravates the course of severe colitis. Hence, regulatory CD25+ T cells within (or developing from) the DP T cell population of MHC class II-deficient mice control the colitogenic potential of CD25- CD4+ T cells.     

Extrathymic derivation of gut lymphocytes in parabiotic mice

In adult mice, c-kit+ stem cells have recently been found in their liver, intestine and appendix, where extrathymic T cells are generated. A major population of such thymus-independent subsets among intraepithelial lymphocytes is T-cell receptor (TCR)gamma delta+ CD4- CD8alpha alpha+(beta-) cells, but the origins of other lymphocyte subsets are still controversial. In this study, we examined what type of lymphocyte subsets were produced in situ by such stem cells in the small intestine, large intestine and appendix. To investigate this subject, we used parabiotic B6.Ly5.1 and B5.Ly5. 2 mice which shared the same circulation by day 3. The origin of lymphocytes was identified by anti-Ly5.1 and anti-Ly5.2 monoclonal antibodies in conjunction with immunofluorescence tests. Lymphocytes in Peyer's patches and lamina propria lymphocytes (especially B cells and CD4+ T cells) in the small intestine became a half-and-half mixture of Ly5.1+ and Ly5.2+ cells in each individual of parabiotic pairs of mice by day 14. However, the mixture was low in CD8alpha alpha+, CD8alpha beta+ and gamma delta T cells in the small and large intestines and in CD3+ CD8+ B220+ cells in the appendix. These cells might be of the in situ origin. When one individual of a pair was irradiated before parabiosis, the mixture of partner cells was accelerated. However, a low-mixture group always continued to show a lower mixture pattern than did a high-mixture group. The present results suggest that extrathymic T cells in the digestive tract may arise from their own pre-existing precursor cells and remain longer at the corresponding sites.     

Intestinal intraepithelial lymphocytes prevent pathogen-driven inflammation and regulate the Smad/T-bet pathway of lamina propria CD4+ T cells

Intraepithelial lymphocytes (IEL) play a key role in gut homeostasis and are critical effector cells preventing the inflammatory intestinal lesions induced in mice following oral infection with Toxoplasma gondii. In this intestinal inflammatory model, CD4(+) T lymphocytes from the lamina propria (LP) synergize with the infected enterocytes to secrete pro-inflammatory chemokines and cytokines. In this study, we assessed the mechanisms accounting for the ability of IEL to modulate the inflammatory activity of these cells. Adoptive transfer of IEL purified from wild-type mice, or CD154-,CD95L- or IL-10-deficient mice infected with T. gondii completely impairs the development of the lethal ileitis in recipient mice orally infected with T. gondii.Compared with unprimed IEL isolated from naive mice, the CD8 alpha beta TCR alpha beta subset of primed IEL, isolated from T. gondii-infected mice, secretes increased amount of TGF-beta. IEL interact with the LP CD4(+) T lymphocytes, down-regulate their production of inflammatory cytokines such as IFN-gamma and reduce their proliferative activity. These effects are linked to the secretion of TGF-beta and are correlated with a shift in the balance between Smad7/T-bet down-regulation and Smad2/Smad3 up-regulation in LP CD4(+) T lymphocytes.     

Subsets of CD3+ (T cell receptor alpha/beta or gamma/delta) and CD3- lymphocytes isolated from normal human gut epithelium display phenotypical features different from their counterparts in peripheral blood

Intestinal intraepithelial lymphocytes (IEL) were studied, after isolation in humans, for their surface antigens with a large variety of monoclonal antibodies. They show peculiar characteristics when compared with peripheral blood lymphocytes and intestinal lamina propria lymphocytes. Although a majority of human intraepithelial lymphocytes (IEL) express an alpha/beta type of T cell receptor (TcR), 13% express a gamma/delta TcR, a percentage which was significantly higher than that found in blood and in lamina propria. In contrast to observations in mice, there was no evidence that normal human TcR gamma/delta+ intestinal IEL might use preferential variable segments of gamma genes. About 10% of human intestinal IEL expressed the alpha chain but not the beta chain of CD8, thus resembling a subset of CD8 alpha+beta- IEL, which was recently described in mice and found to be of thymoindependent origin. In addition, 10% of human IEL had a unique phenotype of immature T cells, as they bore only CD7, but no other T cell or natural killer cell markers. Finally, even the major population of IEL which expressed the usual markers of the T cell lineage (CD3, TcR alpha/beta, CD2, CD4 or CD8 alpha/beta) differed from peripheral blood T lymphocytes by their peculiar expression of surface antigens associated with activation. Indeed, 80% of IEL were CD45R0+, CD45A-, but co-expression of CD11a, CD29 and LFA-3 was inconstant. In addition, 90% of IEL expressed HML-1.     

Lamina Propria T Cell Subsets in the Small and Large Intestine of Euthymic and Athymic Mice

We investigated lamina propria T cells from the small intestine (jejunum/ileum) and the large intestine (colon) of euthymic (BALB/c, C. B-17, C57BL/6) and athymic (C57BL/6 nu/nu; BNX bg/bg nu/nu xid/ xid) mice. CD3⁺ T cells represented about 40% of the lamina propria lymphocytes (LPL) from the small or the large intestine of euthymic mice, and 20–30% of the LPL populations from the small or large intestine of athymic mice. In the lamina propria T cell population of the small intestine, 85% were of the αβ lineage in euthymic mice, but only 40% were of the αβ lineage in athymic mice. T cells of the αβ lineage were thus more frequent than T cells of the αβ lineage in the intestinal lamina propria T cells of extrathymic origin. CD4⁺ T cells represented 40% of the lamina propria T cells in the small as well as in the large intestine of euthymic mice, and 20–30% of the T cells in the lamina propria of the nude mouse gut. In euthymic mice, 40% of the T cells in the small intestine lamina propria, and 30% of the T cells in the colonic lamina propria were CD8⁺, In intestinal lamina propria T cell populations of athymic mice, the CD8⁺ T cell population was expanded. Most (60–70%) CD8+ T cells in the lamina propria of the small and the large intestine of euthymic and athymic mice expressed the homodimeric CD8α⁺β^? form of the CD8 coreceptor. A fraction of 15–20% of all CD3+ T cells in the lamina propria of the small and the large intestine of euthymic and athymic mice were ‘double negative’ CD4^? CD8^?. A large fraction of the TCRαβ⁺ T cells in the colonic lamina propria (but not in the small intestine lamina propria) of euthymic mice expressed the CD2 and the CD28 costimulator molecules, the adhesion molecule LECAM-1 (CD62 L), and could be activated in vitro by CD3 ligation. These data reveal a considerable heterogeneity in the surface phenotype and the functional phenotype of murine lamina propria T cells.     

Expression of T-cell receptors TcR1 (gamma/delta) and TcR2 (alpha/beta) in the human intestinal mucosa.

Cryostat sections of normal human adult gastrointestinal mucosae were studied by double-label immunofluorescence with antibodies to CD3, CD4, CD8, CD5 and CD6, in parallel with antibodies beta F1 and TCR delta 1 against beta-chains and delta-chains of the T-cell receptor (TcR) types TcR2 (alpha/beta) and TcR1 (gamma/delta), respectively. Virtually no TcR1+ were found within the lamina propria. In the epithelial compartment, TcR1+ cells were infrequent: in the small bowel, congruent to 2% of T cells were TcR1+. In the colonic epithelium, the percentage of T cells expressing gamma/delta-chains was higher, with a mean value approximating 15-20%, although this apparently large percentage increase compared with small bowel reflects in part a much lower density of colonic IEL, as absolute numbers of TCR delta 1+ cells were comparable. Of the TcR1+ population, about half were CD4- CD8-, 'double negatives' and the remainder were CD8+. TcR1+ cells were also CD5- CD6-, irrespective of expression of CD8. No CD4+ cells expressing TcR1 were observed: essentially all CD4+ cells were beta F1+, with some variability of labelling intensity. Approximately 30-50% of the CD8+ subset expressed the beta F1 antigen strongly. However, in the remaining TcR1- CD8+ cells, which were all of the CD5- CD6- phenotype, expression of the beta F1 antigen was only detectable when streptavidin and biotin conjugates were used for amplification of labelling. Thus, the CD8+ CD5- subset, a prominent population of the epithelial compartment of the small bowel, was either TcR2dull in the majority or TcR1+ in a minority. Our data imply that gamma/delta TcR1 cells may be actively excluded from intestinal lamina propria, and that any preferential localization that does occur is limited and is rather a feature of the colonic mucosa, rather than the small bowel.     

Microbial colonization influences composition and T-cell receptor V beta repertoire of intraepithelial lymphocytes in rat intestine.

Studies in mice have shown that the composition of intestinal intraepithelial lymphocytes (IEL) may be markedly altered by gut microbial colonization. Such modulation was studied in a rat model by the use of germ-free and conventionalized animals from which IEL from the small intestine were isolated and analysed by flow cytometry. Conventionalization caused expansion as well as phenotypic alterations of T-cell receptor (TCR) alpha/beta + IEL in that the proportions of CD4+ and CD8 alpha beta + TCR alpha/beta + cells were increased, while the double negative (CD4- CD8-) fraction was reduced. microbial colonization also influenced the TCR V beta repertoire of CD8+ IEL in that the proportions of V beta 8.2+ and V beta 10+ cells were increased, whereas V beta 8.5+ and V beta 16+ cells were relatively decreased. Moreover, conventionalization influenced the levels of TCR cell surface expression in the same V beta subsets. Three-colour flow-cytometric analysis demonstrated that skewing of the V beta repertoire was most pronounced in the CD8 alpha alpha + subset, although the numerical increase of IEL mainly included the CD8 alpha beta + subset. In contrast to IEL, the TCR V beta repertoire in mesenteric lymph nodes was unchanged after intestinal colonization. These results confirm that TCR alpha/beta + IEL subpopulations respond dynamically to the microbial gut flora and suggest that their V beta repertoire can be shaped by luminal microbial antigens.     

Changes in the Intestinal Lymphoid Compartment Throughout Life: Implications for the Local Generation of Intestinal T Cells

The intestinal lymphoid compartment has a rather stable composition throughout life. However, both during early neonatal development and at high age unique cell populations can be recognized at distinct sites in the intestinal tissue. Directly after birth all intestinal CD3⁺ cells are found in the lamina propria. At this time the epithelium does not contain T cells. These CD3⁺ lamina propria lymphocytes co-express both TCRβ and TCRδ chains, probably reflecting the expression of a TCRβδ heterodimer on the cell surface. Cells with this particular phenotype are present in comparable numbers in the lamina propria of both neonatal euthymic and athymic mice, indicating the thymus-independent nature of these cells. During aging the frequency of TCRαβ⁺ CD8αα⁺ intestinal T cells increases. These cells are also considered to be thymus-independent. The appearance of high numbers of CD4⁺ CD8αα⁺ intestinal T cells in aged mice is even more striking. It is postulated that the neonatal TCRβδ⁺ cells, and probably also the CD4⁺ CD8αα⁺ cells as found in old mice, are intermediates in the extrathymic differentiation pathway of TCRαβ⁺ CD8αα⁺ intestinal T cells.     

Diverse populations of T cells with NK cell receptors accumulate in the human intestine in health and in colorectal cancer

T cells expressing NK cell receptors (NKR) display rapid MHC-unrestricted cytotoxicity and potent cytokine secretion and are thought to play roles in immunity against tumors. We have quantified and characterized NKR+ T cells freshly isolated from epithelial and lamina propria layers of duodenum and colon from 16 individuals with no evidence of gastrointestinal disease and from tumor and uninvolved tissue from 19 patients with colorectal cancer. NKR+ T cell subpopulations were differentially distributed in different intestinal compartments, and CD161+ T cells accounted for over one half of T cells at all locations tested. Most intestinal CD161+ T cells expressed alpha beta TCR and either CD4 or CD8. Significant proportions expressed HLA-DR,CD69 and Fas ligand. Upon stimulation in vitro, CD161+ T cells produced IFN-gamma and TNF-alpha but not IL-4. NKT cells expressing the Valpha24Vbeta11 TCR, which recognizes CD1d,were virtually absent from the intestine, but colonic cells produced IFN-gamma in response to the NKT cell agonist ligand alpha-galactosylceramide. NKR+ T cells were not expanded in colonic tumors compared to adjacent uninvolved tissue. The predominance, heterogeneity and differential distribution of NKR+ T cells at different intestinal locations suggests that they are central to intestinal immunity.     

TCR-mediated target cell lysis by CD4+NK1+ liver T lymphocytes

In the liver, an unusual T lymphocyte population exists with the intriguing phenotype CD4+NK1+ TCR alpha beta int. Thus far, functions of these lymphocytes remained elusive. Recently, however, CD4+NK1+ liver T lymphocytes have been shown to produce cytokines. Here we show that sorted CD4+NK1+ liver lymphocytes from naive mice lyse target cells after TCR alpha beta or CD3, but not TCR gamma delta, engagement. Liver lymphocytes from beta 2-microglobulin-deficient gene disruption mutant mice failed to express such cytolytic activities and in vivo treatment with anti-NK1.1 mAb or anti-CD4 mAb, but not anti-CD8 mAb, markedly reduced target cell lysis. In vivo administration or rIL-12 impaired TCR alpha beta-mediated target cell lysis by liver lymphocytes. A similar down-regulation of cytolytic activities was observed with liver lymphocytes from mice infected with Listeria monocytogenes or Mycobacterium bovis BCG, which are potent IL-12 inducers. We anticipate (i) that cytolytic CD4+NK1+ T lymphocytes contribute to immunosurveillance of inflammatory processes in the liver and (ii) that they are influenced by IL-12.      

Naturally acquired Pneumocystis carinii pneumonia in gene disruption mutant mice: roles of distinct T-cell populations in infection.

When kept under strict specific-pathogen-free conditions, H-21-Abeta (Abeta(-/-),T-cell receptor beta (TCRbeta(-/-)), and recombinase-activating gene 1 (RAG-1(-/-) gene disruption mutant mice, deficient in conventional CD4+ T cells, TCRalphabeta cells, and all peripheral T and B lymphocytes, respectively, consistently developed lethal Pneumocystis carinii pneumonia through natural infection. The most severe symptoms appeared in RAG-1(-/-) mutants. In contrast, TCRdelta(-/-) and beta2-microglobulin(-/-)(beta2m-/-) mutants, deficient in TCRgammadelta cells and conventional CD8alphabeta+ TCRalphabeta cells, respectively, were fully resistant to infection. Our data indicate not only the insufficiency but also the dispensability of CD8 alphabeta+TCRalphabeta cells and of TCRgammadelta lymphocytes in resistance to P. carinii infection. Under disease conditions, large numbers of unusual single-positive CD4+ and CD8alphabeta+ as well as double-negative TCRgammadelta subpopulations of cells accumulated in lungs of TCRbeta(-/-) mutants. This accumulation was consistently accompanied by a drastic increase in the pulmonary B-cell population. In contrast, CD8alphabeta+ TCR alpha beta cells, but no B cells, appeared in lungs of parasitized Abeta (-/-) mutants. Since lung damage and parasite numbers were less prominent in morbid TCRbeta(-/-) and Abeta(-/-) mutants than in diseased RAG-1(-/-) mice, the remaining lymphocytes accumulating in lungs of the former two mutants seem to perform residual resistance functions.