Phenotypically distinct subsets of CD4+ T cells induce or protect from chronic intestinal inflammation in C. B-17 scid mice

CD4⁺ T cells in the mouse can be subdivided into two fractionsbased on the level of expression of the CD45RB determinant.Previous studies have shown that these subsets are functionallydistinct. We have further characterized the properties of thesesubpopulations in vivo by injecting them into C. B-17 scid mice.The animals restored with the CD45RB^highCD4⁺ T cell populationdeveloped a lethal wasting disease with severe mononuclear cellinfiltrates into the colon and elevated levels of IFN- mRNA.In contrast, animals restored with the reciprocal CD45RB^lowsubset or with unfractionated CD4⁺ T cells did not develop thewasting or colitis. Importantly, the co-transfer of the CD45RB^lowpopulation with the CD45RB^high population prevented the wastingdisease and colitis. These data indicate that important regulatoryinteractions occur between the CD45RB^high and CD45RB^lowCD4⁺T cell subsets and that disruption of this mechanism has fatalconsequences.     

CD45RB expression defines two interconvertible subsets of human CD4+ T cells with memory function

Reciprocal expression of CD45RA and CD45RO in human CD4⁺ T cells defines populations understood to be naive cells (CD45RA⁺CD45RO^?) and memory cells (CD45RA^?CD45RO⁺). We investigate two subsets of CD45RA^?CD45RO⁺ CD4⁺ human T cells which differ by fourfold in their expression of the CD45RB isoform; one is CD45RB^bright and the other is CD45RB^intermediate. In contrast, CD45RA⁺ naive cells are all CD45RB^bright. Both subsets of CD45RA^? cells proliferate in response to recall antigens so we designate them MEM 1 (CD45RO⁺RB^bright) and MEM 2 (CD45RO⁺RB^intermediate). CD45RA and CD45RB expression are regulated independently during in vitro activation of naive cells. When MEM 1 cells are activated they tend to down-regulate CD45RB expression, whereas activated MEM 2 cells tend to up-regulate CD45RB expression. Thus, in contrast to the stability of the CD45RA^?CD45RO⁺ phenotype, the MEM 1 and MEM 2 phenotypes are labile and may interconvert. MEM 1 and MEM 2 cells produced comparable amounts of interleukin(IL)?2, IL?4, and IL-5 though MEM 1 cells produced slightly more interferon(IFN)-γ (mean 1.7-fold more). MEM 1 cells consistently proliferated more (mean 2.3-fold more) than MEM 2 cells early during in vitro activation. Thus, differential expression of CD45RB within CD45RA^? cells defines two subsets that have similar properties except for somewhast greater IFN-γ production and proliferative responses by MEM 1 cells. Variability in CD45RB expression may represent a mechanism for fine-tuning the responsiveness of memory cells in vivo.     

Age-related accumulation of LFA-1high cells in a CD8+CD45RAhigh T cell population

The differential expression of CD45 isoforms has been suggested as a marker for stages of post-thymic T cell development, that is, CD45RA+CD45R0^? T cells and CD45RA^?CD45R0⁺ T cells are supposed to be virgin and memory cells respectively. Recently, several adhesion molecules have been shown to be up-regulated on the cell surface of memory T cells, and have been suggested to serve as a memory marker. In this study, we investigated the levels of LFA-1 expression on T cells in various subpopulations defined by CD45 isoform expression in donors of various ages. In CD4⁺ T cells, the proportion of LFA-1^high cells among CD45RA^highCD45R0-T cells remained low in all age groups and did not show significant accumulation with age. CD4⁺CD45RA^?CD45R0^highTcells expressed LFA-1 at a higher level than CD4⁺CD45RA^highCD45R0^? T cells. Thus, the currently prevailing view that CD45RA and CD45R0 can be markers for virgin and primed cells was consistent with LFA-1 expression in CD4⁺ T cell population. In CD8⁺ T cells, however, CD45RA^highCD45R0^? T cells consisted of two distinct subpopulations, LFA-1^low and LFA-1^high cells, whereas CD45RA^?CD45R0^high T cells were almost exclusively LFA-1^high When CD29 expression was examined in place of LFA-1 expression, similar results were obtained; CD45RA^high CD45R0^? T cells consisted of two distinct subpopulations, CD29-^{to low} and CD^29high cells, while CD45RA-CD45R0^high T cells were mostly CD29^high. The proportion of LFA-1^high cells in the CD8+CD45RA^high T cell subpopulation increased significantly as a function of age (r = 0.9, p < 0.001). It ranged from 8% in a 14-year-old donor to 94% in a 79-year-old donor. Furthermore, the proportion of CD8⁺CD45RA^highLFA-1^high cells in the CD8⁺ T cell population increased significantly as a function of age (r = 0.85, p < 0.001). On the other hand, the proportion of LEA-1^high cells in CD8⁺CD45RA^? T cell subpopulation exceeded 90% in most donors irrespective of age. These results indicate that the CD8⁺CD45RA^highCD45R0^? T cell subpopulation contains a considerable number of LFA-1^high cells and CD29^high cells, phenotypically similar to previously activated cells. Thus, in terms of LFA-1 and CD29 expressions, the simple scheme that CD45RA is a marker of virgin cells is not applicable to the CD8⁺ T cell population.     

Characterization of human CD25+ CD4+ T cells in thymus,cord and adult blood

CD4⁺ CD25⁺ regulatory T cells prevent organ‐specific autoimmune diseases in various animal models. We analysed human lymphoid tissues to identify similar CD25⁺ regulatory T cells. Adult peripheral blood contained two populations of CD4⁺ T cells that expressed CD25 at different densities. The larger population (≈ 40%) expressed intermediate levels of CD25 (CD25⁺) and displayed a memory T‐cell phenotype (CD45RA^?/RO⁺, CD45RB^low, CD95⁺, CD62L^low, CD38^low). The smaller population of cells (≈ 2%) expressed very high levels of CD25 (CD25⁺⁺). In addition to the activation/memory T‐cell antigens mentioned above they also expressed intracellular CD152 (CTLA‐4) as well as enhanced levels of cell‐surface CD122, similar to the murine CD4⁺ CD25⁺ regulatory counterpart. To exclude that the CD25⁺⁺ cells had not been recently primed by external antigen we analysed cord blood and thymus. CD25⁺⁺, CD152⁺ and CD122⁺⁺ cells were present in paediatric thymus (10% of CD4⁺ CD8^? thymocytes) expressing signs of recent selection (CD69⁺) and in cord blood (5% of CD4⁺ cells) where they showed a naive phenotype. In addition, cord blood contained a small population of CD25⁺ cells (≈ 2% of CD4 T cells) that were CD152^? and CD122^low and displayed signs of activation. Together with published data that CD25⁺ CD25⁺⁺ cells from the thymus and peripheral blood are regulatory, our results suggest that regulatory CD25⁺ T cells leave the thymus in a naïve state and become activated in the periphery.     

A population of CD62Llow NK1.1− CD4+ T cells that resembles NK1.1+ CD4+ T cells

In MHC class II−/− C57BL/6 (II−/−) mouse spleen, a small population of CD4⁺ T cells is present of which NK1.1⁺ CD4⁺ (NK) T cells comprise 40 to 45 %. We report here that many of the NK1.1⁻ CD4⁺ T cells derived from II−/− mice are also NK T cells. They produce large amounts of IL-4 in response to anti-CD3 ligation and do so without any requirement for the presence of IL-4 in the priming culture, a property characteristic of NK T cells. Their IFN-γ production is large and is enhanced by IL-12. In addition, II−/− NK1.1⁻ CD4⁺ T cells produce IL-4 as a result of culture with L cells expressing murine CD1 (L-CD1). We report that CD49b, a component of integrin VLA-2, is expressed on the majority of both NK1.1⁺ and NK1.1⁻ NK T cells. NK1.1⁻ NK T cells also exist in wild-type C57BL/6 mice. Evidence supporting this is that Vβ8 usage by CD62L^low NK1.1⁻ CD4⁺ T cells was ∼ 5 % higher than that by CD62L^high CD4⁺ T cells in wild-type mice in keeping with the estimated proportion of NK1.1⁻ NK T cells in the CD62L^low population. CD62L^low CD4⁺ T cells from β2-m−/− mice, which lack NK T cells, showed no increase in Vβ8 usage. When activated by anti-CD3 or L-CD1, CD62L^low NK1.1⁻ CD4⁺ T cells from conventional but not β2-m−/− and CD1−/− mice produce IL-4 in a manner indistinguishable from II−/− NK1.1⁻ CD4⁺ T cells. NK1.1⁻ NK T cells in normal mouse spleens are approximately as numerous as NK1.1⁺ NK T cells.     

Mechanism of enhanced antigen presentation by B cells activated with anti-μ plus interferon-γ: Role of B7-2 in the activation of naive and memory CD4+ T cells

B cells activated with anti-γ antibody plus interferon (IFN)-γ exerted strong antigen presentation activity for T cell proliferation. The enhanced antigen presentation function was shown to be due to the increase in B7-2 expression. When B cells were stimulated with anti-μ, expression of MHC major histocompatibility complex class II, heat-stable antigen (HSA), ICAM-1 and B7-2 was increased. The presence of IFN-γ further augmented the expression of B7-2 on anti-μ-stimulated B cells. B7-1 was not expressed on B cells under these conditions. The participation of B7-2 in the elicitation of the proliferative response of T cells was confirmed by the inclusion of anti-B7-2 antibody in cultures. The enhanced expression of either HSA or ICAM-1 was shown not to play a major role in the increased B cell antigen presentation capacity. The major T cell population responding to this activated B cell antigen presentation was shown to be CD44^low naive CD4⁺ T cells, whereas CD45RB^low memory CD4⁺ T cells responded only weakly. The difference in proliferative responses between naive and memory CD4⁺ T cells was explained by the different efficiency in IL-2 production of these cell populations in response to antigen presentation by B cells activated by anti-μ plus IFN-γ. These results suggest that IFN-γ plays an important role in recruitment of naive T cells for an immune response.     

CD57+ T lymphocytes are derived from CD57− precursors by differentiation occurring in late immune responses

CD3⁺ T cells expressing the 110-kDa CD57 antigen are found in survivors of renal, cardiac and bone marrow transplants, in patients with acquired immune deficiency syndrome and in patients with rheumatoid arthritis. They are also present in normal individuals and expand upon ageing. They do not grow in culture and their role in the immune response is poorly understood. The expression of the various isoforms of the leukocyte common antigen (CD45) identifies a spectrum of differentiation in CD4⁺ and CD8⁺ T cells ranging from naive (CD45RA⁺CD45RB^brightCD45RO^?) through early primed cells (CD45RA^?RB^brightRO^dull) to highly differentiated memory cells which are CD45RA^?RB^dullRO^bright. CD45 isoforms expressed by CD57⁺ T cells showed distinct differences between CD4⁺ and CD8⁺ populations, but in each case indicated an advanced state of differentiation. The expression of T cell receptor Vβ families was highly variable between individuals, but both CD57⁺ and CD57^? cells show a full range of the specificities tested. Vβ expression was more closely related within either the CD4⁺ or the CD8⁺ subsets, irrespective of CD57 expression, than between these subsets, suggesting a relationship between CD57⁺ and CD57^? cells within the same T cell pool. This possibility was supported by experiments showing that CD3⁺CD57⁺ lymphocytes were similar to CD3⁺CD57^? T cells in terms of the production of basic T cell cytokines [interleukin (IL)-2, IL-4, and interferon-γ]. Furthermore, in vitro stimulation of CD3⁺CD57^? T cells in secondary mixed leukocyte reaction or by co-culture with IL-2 and IL-4 induced the appearance of CD3⁺CD57⁺ cells with phenotypic and functional similarities to in vivo CD3⁺CD57⁺ cells. These data strongly suggest that the expression of CD57 is a differentiation event which occurs on CD57^? T cells late in the immune response.     

mTOR signaling promotes a robust and continuous production of IFN‐γ by human memory CD8+ T cells and their proliferation

Human CD8⁺ T cells are functionally heterogeneous and can be divided into phenotypically and functionally distinct subsets according to CCR7 and CD45RA expression levels. Among these, CCR7^lowCD45RA^low effector memory CD8⁺ T cells (Tem) and CCR7^lowCD45RA^high CD8⁺ T cells, which are designated as Temra and considered to be terminally differentiated cells, are Ag‐experienced T cells but show different functionalities. Here, we show that, while Tem proliferate vigorously and produce IFN‐γ persistently and robustly, Temra proliferate poorly and lose the ability to produce IFN‐γ over time after TCR stimulation. Temra showed impaired cell growth upon TCR stimulation, which was associated with defective activation of the mammalian target of rapamycin (mTOR) signaling. Furthermore, rapamycin, an inhibitor of mTOR signaling, interfered with the robust and continuous proliferation of and IFN‐γ production by Tem at later time points after TCR stimulation. Thus, these data collectively indicate that activation of mTOR signaling is required for the robust functions of Tem cells in humans and suggest that defective mTOR signaling in Temra contributes to their functional impairment.     

Staphylococcus aureus convert neonatal conventional CD4+ T cells into FOXP3+ CD25+ CD127low T cells via the PD‐1/PD‐L1 axis

The gut microbiota provides an important stimulus for the induction of regulatory T (Treg) cells in mice, whether this applies to newborn children is unknown. In Swedish children, Staphylococcus aureus has become a common early colonizer of the gut. Here, we sought to study the effects of bacterial stimulation on neonatal CD4⁺ T cells for the induction of CD25⁺ CD127^low Treg cells in vitro. The proportion of circulating CD25⁺ CD127^low Treg cells and their expression of FOXP3, Helios and CTLA‐4 was examined in newborns and adults. To evaluate if commensal gut bacteria could induce Treg cells, CellTrace violet‐stained non‐Treg cells from cord or peripheral blood from adults were co‐cultured with autologous CD25⁺ CD127^low Treg cells and remaining mononuclear cells and stimulated with S. aureus. Newborns had a significantly lower proportion of CD25⁺ CD127^low Treg cells than adults, but these cells were Helios⁺ and CTLA‐4⁺ to a higher extent than in adults. FOXP3⁺ CD25⁺ CD127^low T cells were induced mainly in neonatal CellTrace‐stained non‐Treg cells after stimulation with S. aureus. In cell cultures from adults, S. aureus induced CD25⁺ CD127^low T cells only if sorted naive CD45RA⁺ non‐Treg cells were used, but these cells expressed less FOXP3 than those induced from newborns. Sorted neonatal CD25⁺ CD127^low T cells from S. aureus‐stimulated cultures were still suppressive. Finally, blocking PD‐L1 during stimulation reduced the induction of FOXP3⁺ CD25⁺ CD127^low T cells. These results suggest that newborns have a higher proportion of circulating thymically derived Helios⁺ Treg cells than adults and that S. aureus possess an ability to convert neonatal conventional CD4⁺ T cells into FOXP3⁺ CD25⁺ CD127^low Treg cells via the PD‐1/PD‐L1 axis.     

Mouse and human CD8+ CD28low regulatory T lymphocytes differentiate in the thymus

Regulatory T (Treg) lymphocytes play a central role in the control of immune responses and so maintain immune tolerance and homeostasis. In mice, expression of the CD8 co‐receptor and low levels of the co‐stimulatory molecule CD28 characterizes a Treg cell population that exerts potent suppressive function in vitro and efficiently controls experimental immunopathology in vivo. It has remained unclear if CD8⁺ CD28^low Treg cells develop in the thymus or represent a population of chronically activated conventional T cells differentiating into Treg cells in the periphery, as suggested by their CD28^low phenotype. We demonstrate that functional CD8⁺ CD28^low Treg cells are present in the thymus and that these cells develop locally and are not recirculating from the periphery. Differentiation of CD8⁺ CD28^low Treg cells requires MHC class I expression on radioresistant but not on haematopoietic thymic stromal cells. In contrast to other Treg cells, CD8⁺ CD28^low Treg cells develop simultaneously with CD8⁺ CD28^high conventional T cells. We also identified a novel homologous naive CD8⁺ CD28^low T‐cell population with immunosuppressive properties in human blood and thymus. Combined, our data demonstrate that CD8⁺ CD28^low cells can develop in the thymus of mice and suggest that the same is true in humans.     

Demonstration of identical expanded clones within both CD8+ CD28+ and CD8+ CD28− T cell subsets in HIV type 1-infected individuals

In HIV-1-infected individuals, the CD8⁺ CD28⁻ T cell subset is considerably expanded and is frequently the largest subset of T cells found in peripheral blood. It has been assumed, but not proven, that CD8⁺ CD28⁻ T cells derive from CD8⁺ CD28⁺ T cells in vivo. To further study the ontogeny of CD8⁺ CD28⁻ T cells, we have performed analyses of the complementarity determining region 3 (CDR3) of the TCRB of CD8⁺ CD28⁺ and CD8⁺ CD28⁻ T cells from the peripheral blood of HIV-1-infected individuals. When cells from the same individual were compared, expanded peaks in CDR3 length analysis within a given BV family were frequently observed at the same location in both CD8⁺ subsets ( p < 0.001). Sequencing of cDNA corresponding to dominant peaks revealed the presence of identical expanded CD8⁺ T cell clones within both the CD28⁺ and CD28⁻ subsets on eight of nine attempts. Our results show that CD8⁺ CD28⁺ and CD8⁺ CD28⁻ T cells are phenotypic variants of the same lineage, most likely evolving from CD8⁺ CD28⁺ to end-stage CD8⁺ CD28⁻ T cells.     

CD25+ T cells induce Helicobacter pylori‐specific CD25− T‐cell anergy but are not required to maintain persistent hyporesponsiveness

The gastric pathogen Helicobacter pylori infects over half the world's population. The lifelong infection induces gastric inflammation but the host fails to generate protective immunity. To study the lack of protective H. pylori immunity, CD4⁺CD25⁺ T_reg cells were investigated for their ability to down‐regulate H. pylori‐specific CD4⁺CD25⁻ cells in a murine model. CD25⁻ lymphocytes from infected mice were hyporesponsive to antigenic stimulation in vitro even in the absence of CD25⁺ T_reg cells unless treated with high‐dose IL‐2. Transfer of CD45RB^hi naïve CD25⁻ cells from infected mice into rag1^−/− mice challenged with H. pylori resulted in severe gastritis and reduced bacterial loads, whereas transfer of CD45RB^lo memory CD25⁻ cells from H. pylori‐infected mice resulted in only mild gastritis and persistent infection. CD25⁻ cells stimulated in the absence of CD25⁺ cells in rag1^−/− mice promoted bacterial clearance, but lost this ability when subsequently transferred to WT mice harboring CD25⁺ cells. These results demonstrate that CD25⁺ cells induce anergy in CD25⁻ cells in response to H. pylori infection but are not required to maintain hyporesponsiveness. In addition, CD25⁺ cells are able to suppress previously activated CD25⁻ cells when responding to H. pylori challenge in vivo.     

CD3 antigen-mediated calcium signals and protein kinase C activation are higher in CD45R0+ than in CD45RA+ human T lymphocyte subsets

T lymphocytes may be separated into subsets according to their expression of CD45 isoforms. The CD45R0⁺ T cell subset has been reported to proliferate in response to recall antigen and to mitogenic mAb to a much greater extent than the CD45RA⁺ subset. This difference could be due to more efficient coupling of the T cell antigen receptor complex to mitogenic signaling pathways. To investigate this possibility, CD3 antigen-induced calcium signals, diacylglycerol (DAG) production and protein kinase C (PKC) activation levels were compared in CD45RA⁺ and CD45R0⁺ human T lymphocyte subsets derived from peripheral blood. The mean CD3-induced rise in intracellular calcium was 80% greater in CD45R0⁺ than in CD45RA⁺ cells. Basal DAG levels in CD45R0⁺ cells were found to be, on average, 60% higher than in CD45RA⁺ cells (p = 0.002), but the CD3-induced production of DAG over background was not different in the two subsets (p = 0.4). Basal PKC activity, and CD3-induced PKC activation levels over background, were found to be 50% and 140% higher, respectively, in CD45R0⁺ cells than in CD45RA⁺ cells (p = 0.015 and 0.023). The CD45R0⁺ subset contained a higher proportion of cells expressing activation markers, such as CD25, CD71 and major histocompatibility complex class II, when compared to the CD45RA⁺ subset. Our results suggest that the elevated basal DAG levels observed in the CD45R0⁺ subset may reflect the recent activation of these cells. Both the higher basal DAG and CD3-induced elevation in intracellular calcium observed in the CD45R0⁺ cells may contribute to the greater PKC activation signals triggered by CD3 mAb in this subset. These findings elucidate the greater response of CD45R0⁺ T cells to mitogenic stimuli compared to CD45RA⁺ cells.     

Are primed CD4+ T lymphocytes different from unprimed cells?

Primed and unprimed lymphocytes are usually classified as separate subsets of cells, based on phenotypic and functional distinctions. In the case of CD4⁺ T lymphocytes, primed cells are thought to proliferate more vigorously, quickly and easily, and to release a different profile of cytokines, than their naive equivalent. However, most of these data were obtained from studies in which populations of lymphocytes were compared before and after antigenic stimulation, and therefore did not distinguish between the effects resulting from the clonal expansion of specific precursor cells within such populations and those due to cell differentiation per se. We have investigated the contribution of precursor cell frequency to some of the functional changes observed in populations of CD4⁺ T cells following antigenic stimulation, using approaches in which antigen-specific precursor frequencies are high in both primary and secondary stimulations: mixed leukocyte reaction responses and cells from αβ T cell receptor transgenic mice. Our data suggest that when equivalent numbers of antigen-specific naive and previously primed CD4⁺ responder T cells are compared, there is no difference in their potency to proliferate but only the previously activated subset can generate cytokines such as interferon-γ.     

A novel peripheral CD4+CD8+ T cell population: Inheritance of CD8α expression on CD4+ T cells

In this study we show the inheritance of a CD4⁺CD8⁺ peripheral T cell population in the H.B15 chicken strain. A large proportion of αβ T cells in peripheral blood (20–40%), spleen (10–20%) and intestinal epithelium (5–10%) co-express CD4 and CD8α, but not CD8β. CD4⁺ CD8αα cells are functionally normal T cells, since they proliferate in response to mitogens and signals delivered via the αβT cell receptor as well as via the CD28 co-receptor. These cells induce in vivo a graft versus host-reaction, providing further evidence for their function as CD4⁺ T cells. The CD4⁺CD8αα T cell population was found in 75% of the first progeny and in 100% of further progenies, demonstrating that co-expression of CD4 and CD8 on peripheral T cells is an inherited phenomenon. In addition, cross-breeding data suggest a dominant Mendelian form of inheritance. The hereditary expression of CD8α on peripheral CD4⁺ T cells in chicken provides a unique model in which to study the regulation of CD4 and CD8 expression.     

Evidence that CD4+, but not CD8+ T cells are responsible for murine interleukin-2-deficient colitis

Mice deficient in interleukin-2 production (IL-2^null mice) develop colonic inflammation closely resembling ulcerative colitis in humans. Although this disease is marked by substantial infiltration of the colon by CD8⁺ and CD4⁺ T lymphocytes, no function has yet been assigned to these T cell subsets in the development of colitis in the IL-2^null mouse. For the present study, we investigated the involvement of T lymphocytes in the onset of colitis in IL-2^null mice, and examined the possible role played by cytotoxic T cells. Both lamina propria lymphocytes (LPL) and intraepithelial lymphocytes (IEL) of the colon of IL-2^null mice were potently cytotoxic ex vivo in short-term redirected cytotoxic lymphocyte (CTL) assays. In contrast, colonic T cells of wild-type animals showed little or no constitutive cytotoxic T cell activity. Colonic CTL were detectable prior to the appearance of disease in IL-2^null animals and CTL activity was confined to the TcRαβ, rather than to the TcRγδ IEL subset. IL-2^null animals crossed with major histocompatibility complex class I-deficient mice [IL-2^null × β₂ microglobulin (β₂m^null] mice also developed colitis, which appeared even earlier than in most IL-2^null mice. These findings suggest that neither CD8⁺ IEL nor LPL were causal in the onset of colitis in IL-2^null animals. In IL-2^null × β₂m^null mice, an ulcerative colitis-like disease was evident from histological studies and immunohistological staining which showed very large numbers of CD4⁺ lymphocytes within the intestinal mucosa. Significant ex vivo killing by CD4⁺ T cells was observed in IL-2^null × β₂m^null animals, although this required an extended incubation time compared to colonic CD8⁺ T cells. Peripheral as well as colonic CD4⁺ T cells in IL-2^null and IL-2^null × β₂m^null animals, were activated as judged by their cell surface phenotype (CD45RB^lo, L-selectin^lo and CD69⁺). In light of these findings, we propose that infiltrating CD4⁺, but not CD8⁺ T cells are central to the inflammation observed in the intestinal mucosa in IL-2^null colitis.     

Mesenteric lymph node CD11b− CD103+ PD‐L1High dendritic cells highly induce regulatory T cells

Dendritic cells (DCs) in mesenteric lymph nodes (MLNs) induce Foxp3⁺ regulatory T cells to regulate immune responses to beneficial or non‐harmful agents in the intestine, such as commensal bacteria and foods. Several studies in MLN DCs have revealed that the CD103⁺ DC subset highly induces regulatory T cells, and another study has reported that MLN DCs from programmed death ligand 1 (PD‐L1) ‐deficient mice could not induce regulatory T cells. Hence, the present study investigated the expression of these molecules on MLN CD11c⁺ cells. Four distinct subsets expressing CD103 and/or PD‐L1 were identified, namely CD11b⁺ CD103⁺ PD‐L1^High, CD11b⁻ CD103⁺ PD‐L1^High, CD11b⁻ CD103⁺ PD‐L1^Low and CD11b⁺ CD103⁻ PD‐L1^Int. Among them, the CD11b⁻ CD103⁺ PD‐L1^High DC subset highly induced Foxp3⁺ T cells. This subset expressed Aldh1a2 and Itgb8 genes, which are involved in retinoic acid metabolism and transforming growth factor‐β (TGF‐β) activation, respectively. Exogenous TGF‐β supplementation equalized the level of Foxp3⁺ T‐cell induction by the four subsets whereas retinoic acid did not, which suggests that high ability to activate TGF‐β is determinant for the high Foxp3⁺ T‐cell induction by CD11b⁻ CD103⁺ PD‐L1^High DC subset. Finally, this subset exhibited a migratory DC phenotype and could take up and present orally administered antigens. Collectively, the MLN CD11b⁻ CD103⁺ PD‐L1^High DC subset probably takes up luminal antigens in the intestine, migrates to MLNs, and highly induces regulatory T cells through TGF‐β activation.     

IL‐2 is positively involved in the development of colitogenic CD4+ IL‐7Rαhigh memory T cells in chronic colitis

IL‐2 and IL‐7 share a common γ‐chain receptor and are critical for T‐cell homeostasis. We aimed to clarify the reciprocal roles of IL‐2 and IL‐7 in the development and persistence of chronic colitis. We performed a series of adoptive transfers of IL‐2^?/? CD4⁺CD45RB^high T cells into RAG‐2^?/? mice and assessed the role of IL‐2 in the induction of IL‐7Rα on colitogenic CD4⁺ T cells and the development of chronic colitis. RAG‐2^?/? mice transferred with WT but not with IL‐2^?/? CD4⁺CD45RB^high T cells developed Th1/Th17‐mediated colitis. Consistently, re‐expression of IL‐7Rα was severely impaired on IL‐2^?/? but not on WT CD4⁺ T cells from the transferred mice. To exclude a contribution of the preclinical autoimmunity of IL‐2^?/?mice, WT Ly5.1⁺ or IL‐2^?/? Ly5.2⁺ CD4⁺CD45RB^high T cells from GFP mice previously transplanted with the same number of WT and IL‐2^?/? BM cells were transferred into RAG‐2^?/? mice. RAG‐2^?/? mice transferred with IL‐2^?/?‐derived CD4⁺CD45RB^high T cells did not develop colitis, but their splenic CD4⁺ T cells changed from effector‐memory to central‐memory type. These results show that IL‐2 is critically involved in the establishment and maintenance of IL‐7‐dependent colitogenic memory CD4⁺IL‐7Rα^high T cells.