Expression of selectin-binding epitopes and cytokines by CD4+ T cells repopulating scid mice with colitis

Regulation and migratory role of P-selectin ligands during intestinal inflammation

Dendritic cells from mesenteric lymph nodes (MLN) can convert retinal to retinoic acid (RA), which promotes induction of the gut-specific homing receptor α4β7. In contrast, priming within peripheral lymph nodes leads to upregulation of E- and P-selectin ligands (E- and P-lig). Apart from its α4β7 promoting effect, RA was shown to suppress E- and P-lig induction in vitro. However, enhanced frequencies of P-lig(+) CD4(+) T cells were reported during intestinal inflammation. To understand this contradiction, we first determined whether location of intestinal inflammation, that is, ileitis or colitis, affects P-lig induction. Both conditions promoted P-lig expression on CD4(+) T cells; however, P-lig expressed on T cells facilitated Th1 cell recruitment only into the inflamed colon but not into inflamed small intestine induced by oral Toxoplasma gondii infection. A majority of P-lig(+)CD4(+) T cells found within MLN during intestinal inflammation co-expressed α4β7 confirming their activation in the presence of RA. Mesenteric P-lig(+)CD4(+) cells co-expressed the 130 kDa isoform of CD43 which requires activity of core 2 (beta)1,6-N-acetyl-glycosaminyltransferase-I (C2GlcNAcT-I) suggesting that C2GlcNAcT-I contributes to P-lig expression under these conditions. To test whether inflammatory mediators can indeed overrule the inhibitory effect of RA on P-lig expression we stimulated CD4(+) T cells either polyclonal in the presence of IL-12 and IFNγ or by LPS-activated MLN-derived dendritic cells. Both conditions promoted P-lig induction even in the presence of RA. While RA impeded the induction of fucosyltransferase-VII it did not affect IL-12-dependent C2GlcNAcT-I induction suggesting that C2GlcNAcT-I can support P-lig expression even if fucosyltransferase-VII mRNA upregulation is dampened.

Dendritic cell immunization route determines integrin expression and lymphoid and nonlymphoid tissue distribution of CD8 T cells

Exogenous dendritic cells (bone marrow-derived dendritic cell (BMDC)) display restricted trafficking in vivo after injection into mice, but the route(s) by which they generate gut-homing effector cells is unclear. Mesenteric lymph nodes (LN) and spleen were differentially targeted by i.p. and i.v. administration of BMDC, respectively, whereas mediastinal LN were targeted by both routes. BMDC injected by either route activated CD8(+) T cells to up-regulate both alpha(4)beta(1) and alpha(4)beta(7) integrins. However, the lymphoid compartment in which activation occurred determined their expression kinetics, magnitude, and population distribution. Only T cells activated in mesenteric LN after i.p. immunization expressed high levels of alpha(4)beta(7), which also correlated with localization to small intestine. These alpha(4)beta(7)(high) cells also redistributed to mediastinal LN in a manner sensitive to treatment with alpha(4)beta(7) blocking Abs, but not to mucosal addressin cell adhesion molecule-1 blocking Abs. Our results demonstrate the importance of lymphoid compartment, as dictated by immunization route, in determining integrin expression on activated T cells and their distribution in lymphoid and nonlymphoid tissues.

Microenvironment-dependent requirement of STAT4 for the induction of P-selectin ligands and effector cytokines on CD4+ T cells in healthy and parasite-infected mice

T effector cells require selectin ligands to migrate into inflamed regions. In vitro, IL-12 promotes induction of these ligands as well as differentiation of CD4+ T cells into IFN-gamma-producing Th1 but not Th2 cells. STAT4 is strongly involved in these processes. However, the presence of selectin ligands on various T effector cell subsets in vivo points to more complex regulatory pathways. To clarify the role of the IL-12/STAT4 signaling pathway, we analyzed the impact of STAT4 deficiency on the expression of P-selectin ligands (P-lig) on CD4+ T cells in vitro and in vivo, including conditions of infection. In vitro, we found significant expression of P-lig upon activation not only in the presence, but also in the absence, of IL-12, which was independent of STAT4. TGF-beta, an alternative inducer of selectin ligands in human T cells, was not effective in murine CD4+ T cells, suggesting a role of additional signaling pathways. In vivo, a significant impact of STAT4 for the generation of P-lig+CD4+ T cells was observed for cells from peripheral lymph nodes, but not for those from spleen or lung. However, upon infection with the Th2-inducing parasite Nippostrongylus brasiliensis, P-lig expression became dependent on STAT4 signaling. Interestingly, also the frequency of IL-4-producing cells was greatly diminished in absence of STAT4. These data reveal a hitherto unknown contribution of STAT4 to the generation of Th2 cells in parasite infection and suggest that signals inducing inflammation-seeking properties in vivo vary depending on environmental conditions, such as type of organ and infection.

Expression of selectin ligands on murine effector and IL-10-producing CD4+ T cells from non-infected and infected tissues

Endothelial selectins are crucial for the recruitment of leukocytes into sites of inflammation. On T cells, ligands for selectins become induced upon differentiation into the effector/memory stage. Initial in vitro studies suggested a correlation between the Th1 phenotype and ligand expression, but whether this also holds true in vivo remained uncertain. We here analyzed selectin ligands on CD4+ T cells producing IFN-gamma, IL-4 or IL-10, prototypic cytokines of the Th1, Th2 and Tr1 subset, respectively. We analyzed mice infected with influenza virus, the bacterium Listeria, and the parasites Toxoplasma (all Th1 models) or Nippostrongylus (Th2 model). A link between the Th1 phenotype and ligand expression was not found in vivo. Surprisingly, the potentially regulatory IL-10-producing T cells displayed the highest frequency of ligand-positive cells in general. Within the inflamed tissues, the frequencies of P-selectin-binding cells increased in the dominant subset, either Th1 or Th2. Up-regulation was also found for E-selectin ligands during influenza, but not Nippostrongylus infection. In conclusion, conditions driving T cell polarization into either Th1 or Th2 in vivo do not affect the expression of selectin ligands, but acquisition of P-selectin binding and hence migration into inflamed tissues is boosted by an inflammatory milieu.

IL-12 administration accelerates autoimmune diabetes in both wild-type and IFN-gamma-deficient nonobese diabetic mice, revealing pathogenic and protective effects of IL-12-induced IFN-gamma

IL-12 administration to nonobese diabetic (NOD) mice induces IFN-gamma-secreting type 1 T cells and high circulating IFN-gamma levels and accelerates insulin-dependent diabetes mellitus (IDDM). Here we show that IL-12-induced IFN-gamma production is dispensable for diabetes acceleration, because exogenous IL-12 could enhance IDDM development in IFN-gamma-deficient as well as in IFN-gamma-sufficient NOD mice. Both in IFN-gamma(+/-) and IFN-gamma(-/-) NOD mice, IL-12 administration generates a massive and destructive insulitis characterized by T cells, macrophages, and CD11c(+) dendritic cells, and increases the number of pancreatic CD4(+) cells secreting IL-2 and TNF-alpha. Surprisingly, IL-12-induced IFN-gamma hinders pancreatic B cell infiltration and inhibits the capacity of APCs to activate T cells. Although pancreatic CD4(+) T cells from IL-12-treated IFN-gamma(-/-) mice fail to up-regulate the P-selectin ligand, suggesting that their entry into the pancreas may be impaired, T cell expansion is favored in these mice compared with IL-12-treated IFN-gamma(+/-) mice because IL-12 administration in the absence of IFN-gamma leads to enhanced cell proliferation and reduced T cell apoptosis. NO, an effector molecule in beta cell destruction, is produced ex vivo in high quantity by pancreas-infiltrating cells through a mechanism involving IL-12-induced IFN-gamma. Conversely, in IL-12-treated IFN-gamma-deficient mice, other pathways of beta cell death appear to be increased, as indicated by the up-regulated expression of Fas ligand on Th1 cells in the absence of IFN-gamma. These data demonstrate that IFN-gamma has a dual role, pathogenic and protective, in IDDM development, and its deletion allows IL-12 to establish alternative pathways leading to diabetes acceleration.

Cytokine memory of T helper lymphocytes

Memory is one of the key features of the adaptive immune system. Specific T and B lymphocytes are primed for a particular antigen and upon challenge with it will react faster than naive lymphocytes. They also memorize the expression of key effector molecules, in particular cytokines, which determine the type and scale of an immune reaction. While in primary activations differential expression of cytokine genes is dependent on antigen-receptor signaling and differentiation signals, in later activations the expression is triggered by antigen-receptor signaling and dependent on the cytokine memory. The molecular basis of the cytokine memory implies differential expression of transcription factors and epigenetic modifications of cytokine genes and gene loci. GATA-3 for Th2 and T-bet for Th1 cells expressing interleukin-4 or interferon-gamma, respectively, are prime candidates for key transcription factors of cytokine memory. The essential role of epigenetic modifications is suggested by the requirement of DNA synthesis for the establishment of a cytokine memory in Th lymphocytes. At present the molecular link between transcription factors and epigenetic modifications of cytokine genes in the establishment and maintenance of cytokine memory is not clear. The initial cytokine memory is not stable against adverse differentiation signals, while in repeatedly stimulated lymphocytes it is stabilized by a variety of mechanisms.

Homeostasis of intestinal immune regulation

Regulatory CD4 T cells with the capacity to inhibit potentially harmful immune responses have been described in various experimental systems. Although the observations are converging towards the naturally activated CD25(+) CD4 T cells as a major population responsible for this protection, there is still considerable disagreement on the molecular and cellular requirements involved to achieve a stable immune homeostasis in vivo.

Monocyte/macrophage initiation of organ-specific autoimmunity: the ultimate 'bystander' hypothesis?

It is postulated that organ-specific autoimmune diseases could be initiated by dysregulated peripherally activated monocytes/macrophages penetrating into target organs nonspecifically. Failure of regulation of pro-inflammatory monocytes/macrophages might then result in autoimmune disease if secondary over-expansion of pre-existing autoantigen-specific T cell populations occurs in genetically predisposed individuals.

Tumor-specific responses in lymph nodes draining murine sarcomas are concentrated in cells expressing P-selectin binding sites

Tumor-draining lymph node (TDLN) cells develop substantial antitumor activity after activation on immobilized alphaCD3 and culture in low-dose IL-2. This study found that the minor subset of TDLN T cells expressing binding sites for the adhesion receptor P-selectin (Plig(high) T cells) produced T lymphoblasts with the most tumor-specific IFN-gamma synthesis in vitro and antitumor activity following adoptive transfer in vivo. The Plig(high) T cells constituted <25% of the cells with the phenotype of recently activated cells including high levels of CD69, CD44, or CD25, and low levels of CD62L. The cultured Plig(high) TDLN were 10- to 20-fold more active against established pulmonary micrometastases than cultured unfractionated TDLN, and >30-fold more active than cultured TDLN cells depleted of the Plig(high) fraction before expansion (Plig(low) cells). Tumor-specific IFN-gamma synthesis in vitro paralleled the antitumor activities of the cultured fractions in vivo, implying that increased Tc1 and Th1 effector functions contributed to the tumor suppression. Neither nonspecific interaction with the P-selectin chimera used for sorting nor endogenous costimulatory activity in the Plig(high) fraction accounted for the marked increase in antitumor activities after culture. The cultured Plig(high) fraction contained a variety of potential effector cells; however, the CD8 and CD4 subsets of alphabeta T cells accounted for 95-97% of its antitumor activity. The authors propose that P-selectin sorting increased antitumor activities by concentrating Tc1 and Th1 pre-effector/effector cells before culture.

Composition and arrangement of genes define the strength of IRES-driven translation in bicistronic mRNAs

In addition to the cap-dependent mechanism, eukaryotic initiation of translation can occur by a cap-independent mechanism which directs ribosomes to defined start codons enabled by internal ribosome entry site (IRES) elements. IRES elements from poliovirus and encephalomyocarditis virus are often used to construct bi- or oligocistronic expression vectors to co-express various genes from one mRNA. We found that while cap-dependent translation initiation from bicistronic mRNAs remains comparable to monocistronic expression, internal initiation mediated by these viral IRESs is often very inefficient. Expression of bicistronic expression vectors containing the hepatitis B virus core antigen (HBcAg) together with various cytokines in the second cistron of bicistronic mRNAs gave rise to very low levels of the tested cytokines. On the other hand, the HBcAg was well expressed when positioned in the second cistron. This suggests that the arrangement of cistrons in a bicistronic setting is crucial for IRES-dependent translation of the second cistron. A systematic examination of expression of reporter cistrons from bicistronic mRNAs with respect to position was carried out. Using the dual luciferase assay system we show that the composition of reading frames on a bicistronic mRNA and the order in which they are arranged define the strength of IRES-dependent translation. Although the cellular environment and the nature of the IRES element influence translation strength the dominant determinant is the nature and the arrangement of cistrons on the mRNA.

Persistence of pathogenic CD4+ Th1-like cells in vivo in the absence of IL-12 but in the presence of autoantigen

Despite recent successful treatment of murine autoimmune disease with anti-IL-12 mAb, it has not yet been addressed whether anti-IL-12 mAb can also be effective in late stages of disease and whether it can provide lasting protection against recurrence, especially during continued presence of autoantigen. We used a newly developed psoriasis model in scid/scid mice, which allows easy tracking of pathogenic T cells, to show that when anti-IL-12 mAb is given for 2 wk (1 mg/wk) in the late stage of severe disease, inflammation is greatly reduced, as measured by ear thickness and histology (scores, 1.1 +/- 0.1 vs 2.0 +/- 0.4). Moreover, prolonged treatment (4 wk) of chronic psoriatic mice with high doses of mAb (1 mg/wk; prolonged active anti-inflammatory treatment (PAAIT)) results in the almost complete resolution of lesions (scores, 0.3 +/- 0.1 vs 2.7 +/- 0.2). Surprisingly, however, despite these significant treatment results, the psoriasis-like lesions return soon after the anti-IL-12 mAb treatment is discontinued. This rapid relapse of disease may be attributed to large populations of activated CD4(+) T cells present in the lymph nodes of PAAIT animals still expressing an effector/memory phenotype (CD45RB(low), L-selectin(low)). Upon stimulation in vitro such PAAIT lymph node cells secrete high amounts of IFN-gamma (129 ng/ml); when transferred into naive scid/scid animals they are able to rapidly induce disease without costimulation. Our data indicates an alternative IL-12-independent pathway for pathogenic Th-1-like cells in vivo during the chronic phase of disease that allows these cells to persist and maintain their pathogenicity in the draining lymph tissue of the autoimmune site.

CD25+ CD4+ T cells regulate the expansion of peripheral CD4 T cells through the production of IL-10

The mechanisms by which the immune system achieves constant T cell numbers throughout life, thereby controlling autoaggressive cell expansions, are to date not completely understood. Here, we show that the CD25(+) subpopulation of naturally activated (CD45RB(low)) CD4 T cells, but not CD25(-) CD45RB(low) CD4 T cells, inhibits the accumulation of cotransferred CD45RB(high) CD4 T cells in lymphocyte-deficient mice. However, both CD25(+) and CD25(-) CD45RB(low) CD4 T cell subpopulations contain regulatory cells, since they can prevent naive CD4 T cell-induced wasting disease. In the absence of a correlation between disease and the number of recovered CD4(+) cells, we conclude that expansion control and disease prevention are largely independent processes. CD25(+) CD45RB(low) CD4 T cells from IL-10-deficient mice do not protect from disease. They accumulate to a higher cell number and cannot prevent the expansion of CD45RB(high) CD4 T cells upon transfer compared with their wild-type counterparts. Although CD25(+) CD45RB(low) CD4 T cells are capable of expanding when transferred in vivo, they reach a homeostatic equilibrium at lower cell numbers than CD25(-) CD45RB(low) or CD45RB(high) CD4 T cells. We conclude that CD25(+) CD45RB(low) CD4 T cells from nonmanipulated mice control the number of peripheral CD4 T cells through a mechanism involving the production of IL-10 by regulatory T cells.

Flow cytometric measurement of intracellular cytokines

The identification of distinct T helper lymphocyte subsets (Th1/2) with polarised cytokine production has opened up new fields in immunobiology. Of the several alternative methods of monitoring cytokine production, flow cytometric analysis of intracellular staining has distinct advantages and pitfalls. It allows high throughput of samples and multiparameter characterisation of cytokine production on a single cell basis without the need for prolonged in vitro culture and cloning. However, these methods may cause important changes in cell surface phenotype which can make interpretation difficult.

Regulatory CD4 T cells control the size of the peripheral activated/memory CD4 T cell compartment

The mechanisms leading to stable T cell numbers in the periphery of a healthy animal are, to date, not well understood. We followed the expansion of CD45RBhigh (naive) and CD45RBlow (activated/memory) CD4 T cells transferred from normal mice into syngeneic Rag-20/0 recipients and the dynamics of peripheral reconstitution when both populations were coinjected. Naive cells acquired an activated phenotype and showed a high proliferative capacity that was dependent on the environment in which the recipients were kept (specific pathogen-free vs conventional housing conditions), the age of the recipients, and the presence of CD45RBlow T cells in the injected cohort. CD45RBlow CD4 T cells protected the host from CD45RBhigh CD4 T cell-induced inflammatory bowel disease and showed a limited degree of expansion. CD45RBlow CD4 T cells isolated from GF mice also showed the ability to prevent inflammatory bowel disease, indicating that at least part of the natural regulatory T cells are self-reactive. The results indicate that 1) peripheral T cell expansion in lymphocyte-deficient recipients represent classical immune responses, which are mainly promoted by exogenous Ags and 2) natural regulatory T cells control the size of the activated/memory peripheral CD4 T cell compartment.

Th1/Th2 subsets: distinct differences in homing and chemokine receptor expression?

The functional specialization of T effector cells according to cytokine secretion patterns has been recognized as an important parameter shaping local immune responses. Here we discuss evidence that T cell subsets might also develop distinctive properties related to homing and trafficking into inflamed sites. First, ligands for the inflammation-induced endothelial selectins were found to be induced by IL-12, and hence selectively expressed on Th1 cells generated in vitro. However, their expression on effector cells occurring in vivo is less well correlated with the Th subset. Second, a variety of receptors for and responses towards chemokines have been found to be differentially associated with Th subsets. Notably CCR5 and, to a lesser degree CXCR3 were preferentially found on Th1 cells, CCR4, CCR8 and, more controversial, CCR3 and CXCR4 on Th2 cells. Although many points, such as stability of the phenotype versus dependency on inducing cytokines and activation stages remain to be clarified, it appears that this field provides new insights into the regulation of locally balanced activities of Th subsets and might constitute a promising field for the development of new immunosuppressive drugs.

Animal models of mucosal inflammation and their relation to human inflammatory bowel disease

Animal models of inflammatory bowel disease (IBD) have been useful in the identification of those immune responses uniquely involved in IBD pathogenesis and in defining the important roles of environmental influences, such as normal luminal bacterial flora and the genetic composition of the host, in modifying IBD-associated inflammation. Recent studies have focused particular attention on CD4+ T cells which produce excessive quantities either of Th1 cytokines (IFN-gamma and TNF) directed by IL-12 or of a Th2 cytokine (IL-4), relative to the production of suppressive cytokines such as IL-10 and transforming growth factor beta. Such insights will be extremely beneficial in the development of novel approaches to the control of IBD-type inflammation, such as the use of anticytokine therapies and gene therapy, and finally, in the identification of the genetic abnormalities and the antigens driving the inflammation that underlies the human disease.

Tissue Specificity of E- and P-Selectin Ligands in Th1-Mediated Chronic Inflammation

The demonstrated role of E- and P-selectin ligands in the recruitment of Th1 cells raises the question of tissue specificity determination by pathogenic T cells. We took advantage of the fact that chronic Th1-mediated inflammation in the scid/scid CD4+CD45RBhigh T cell transfer model can occur at multiple tissue sites, resembling inflammatory bowel disease in the colon and psoriasis in the skin. We show that the majority of infiltrating effector T cells from psoriatic skin expresses high levels of functional P-selectin ligand (87 ± 3%), detected by P-selectin-Ig (PIg), while a significantly smaller subset of T cells from colitic lesions expresses this ligand (24 ± 2%). Similarly, E-selectin ligand is preferentially expressed on CD4+ T cells infiltrating the skin (24 ± 2%), but only on very few CD4+ T cells infiltrating the colon (CIT; 1.3 ± 0.8%). In contrast, CD4+ T cells infiltrating the skin express α4β7 at a significantly lower level than CIT (mean fluorescence intensity, 28 vs 61, respectively), although, interestingly, αEβ7 was expressed at high levels on both populations. Analysis of the disease-inducing potential of PIg+ and PIg− CD4+ CIT cells revealed that both populations not only express similar levels of the gut-homing molecule α4β7 (mean fluorescence intensity, 50 vs 56, respectively), but do not differ in their capacity to express IFN-γ. Furthermore, CIT depleted of cells expressing functional P-selectin ligand were able to induce colitis upon transfer, suggesting that induction of colitis in this model may be independent of E- and P-selectin. These results indicate that adhesion molecule expression and the homing pattern of inflammatory T cells are regulated by the local environment independently of their inflammatory capacity.

In vitro activated CD4+ T cells from interferon-gamma (IFN-gamma)-deficient mice induce intestinal inflammation in immunodeficient hosts

To investigate the role of IFN-gamma in the immunopathogenesis of inflammatory bowel disease (IBD), severe combined immunodeficient (SCID) mice were transplanted with in vitro activated CD4+ T cells from either wild-type (WT) or IFN-gamma-deficient (IFN-gammaKO) BALB/c mice. In vitro, the two types of T cells displayed comparable proliferation rates and production of tumour necrosis factor-alpha (TNF-alpha), IL-2, IL-4 and IL-10 after concanavalin A (Con A) stimulation. When transplanted into SCID mice, WT CD4+ blasts induced a lethal IBD, whereas IFN-gammaKO blasts induced a less severe intestinal inflammation with moderate weight loss. Intracellular cytokine staining of lamina propria lymphocytes (LPL) revealed comparable fractions of CD4+ T cells positive for TNF-alpha, IL-2 and IL-10 in the two groups of transplanted SCID mice, whereas a two-to-three-fold increase in the fraction of IL-4-positive cells was found in IFN-gammaKO-transplanted SCID mice. Flow cytometric analyses showed strong up-regulation of MHC class II expression of colonic epithelial cells of WT-CD4+ T cell-transplanted compared with IFN-gammaKO-transplanted SCID mice. A significantly higher fraction of CD4+ LPL were found to enter the cell cycle, i.e. to incorporate bromo-deoxy-uridine, and to undergo apoptosis in vivo in WT-transplanted compared with IFN-gammaKO-transplanted SCID mice. These data point towards an important role for IFN-gamma in the development of IBD in SCID mice. The inflammation might be initiated and subsequently enhanced by the ability of IFN-gamma to induce de novo MHC class II expression in the colonic epithelium, a change which could lead to increased antigen processing and production of local proinflammatory cytokines, CD4+ T cell turnover and thereby to exaggeration of disease.

Pancreas-Infiltrating Th1 Cells and Diabetes Develop in IL-12-Deficient Nonobese Diabetic Mice

IL-12 and IL-12 antagonist administration to nonobese diabetic (NOD) mice accelerates and prevents insulin-dependent diabetes mellitus (IDDM), respectively. To further define the role of endogenous IL-12 in the development of diabetogenic Th1 cells, IL-12-deficient NOD mice were generated and analyzed. Th1 responses to exogenous Ags were reduced by ∼80% in draining lymph nodes of these mice, and addition of IL-12, but not IL-18, restored Th1 development in vitro, indicating a nonredundant role of IL-12. Moreover, spontaneous Th1 responses to a self Ag, the tyrosine phosphatase-like IA-2, were undetectable in lymphoid organs from IL-12-deficient, in contrast to wild-type, NOD mice. Nevertheless, wild-type and IL-12-deficient NOD mice developed similar insulitis and IDDM. Both in wild-type and IL-12-deficient NOD mice, ∼20% of pancreas-infiltrating CD4+ T cells produced IFN-γ, whereas very few produced IL-10 or IL-4, indicating that IDDM was associated with a type 1 T cell infiltrate in the target organ. T cell recruitment in the pancreas seemed favored in IL-12-deficient NOD mice, as revealed by increased P-selectin ligand expression on pancreas-infiltrating T cells, and this could, at least in part, compensate for the defective Th1 cell pool recruitable from peripheral lymphoid organs. Residual Th1 cells could also accumulate in the pancreas of IL-12-deficient NOD mice because Th2 cells were not induced, in contrast to wild-type NOD mice treated with an IL-12 antagonist. Thus, a regulatory pathway seems necessary to counteract the pathogenic Th1 cells that develop in the absence of IL-12 in a spontaneous chronic progressive autoimmune disease under polygenic control, such as IDDM.

Colitis-Inducing Potency of CD4+ T Cells in Immunodeficient, Adoptive Hosts Depends on Their State of Activation, IL-12 Responsiveness, and CD45RB Surface Phenotype

We studied the induction, severity, and rate of progression of inflammatory bowel disease (IBD) induced in SCID mice by the adoptive transfer of low numbers of the following purified BALB/c CD4+ T cell subsets: 1) unfractionated, peripheral, small (resting), or large (activated) CD4+ T cells; 2) fractionated, peripheral, small, or large, CD45RBhigh or CD45RBlow CD4+ T cells; and 3) peripheral IL-12-unresponsive CD4+ T cells from STAT-4-deficient mice. The adoptive transfer into SCID host of comparable numbers of CD4+ T cells was used to assess the colitis-inducing potency of these subsets. Small CD45RBhigh CD4+ T lymphocytes and activated CD4+ T blasts induced early (6–12 wk posttransfer) and severe disease, while small resting and unfractionated CD4+ T cells or CD45RBlow T lymphocytes induced a late-onset disease 12–16 wk posttransfer. SCID mice transplanted with STAT-4−/− CD4+ T cells showed a late-onset IBD manifest &gt;20 wk posttransfer. In SCID mice with IBD transplanted with IL-12-responsive CD4+ T cells, the colonic lamina propria CD4+ T cells showed a mucosa-seeking memory/effector CD45RBlow Th1 phenotype abundantly producing IFN-γ and TNF-α. In SCID mice transplanted with IL-12-unresponsive STAT-4−/− CD4+ T cells, the colonic lamina propria, mesenteric lymph node, and splenic CD4+ T cells produced very little IFN-γ but abundant levels of TNF-α. The histopathologic appearance of colitis in all transplanted SCID mice was similar. These data indicate that CD45RBhigh and CD45RBlow, IL-12-responsive and IL-12-unresponsive CD4+ T lymphocytes and lymphoblasts have IBD-inducing potential though of varying potency.

Proliferation and apoptosis of lamina propria CD4+ T cells from scid mice with inflammatory bowel disease

Scid mice transplanted with low numbers of syngeneic CD4+ T cells, develop a chronic and lethal inflammatory bowel disease (IBD) within 4-6 months. We have used in vivo 5-bromo2-deoxy-uridine (BrdU) labeling to assess the proliferation of lamina propria-derived CD4+ T cells in diseased scid mice. The hourly rate of renewal of colonic lamina propria CD4+ T cells in diseased mice was 7% compared with 1.5% in normal BALB/c control mice. Transplantation of scid mice with in vitro activated CD4+ T cells accelerated the disease onset and development in a cell dose-dependent fashion when compared with non-activated CD4+ T cells. In pulse-chase experiments it was shown that BrdU-labeled cells disappeared rapidly from the lamina propria of diseased mice. DNA analysis revealed that this was due to the presence of nearly four times as many apoptotic CD4+ T cells in diseased than in control mice. Further analyses showed that the apoptotic lamina propria CD4+ T cells were derived from cells having entered the cell cycle within the previous 8 h. These data clearly demonstrate that vigorous CD4+ T cell proliferation and death are involved throughout the course of IBD.

CD4+ T Cells Migrate into Inflamed Skin Only If They Express Ligands for E- and P-Selectin

Previous data suggested a role of endothelial selectins in skin homing of lymphocytes. In the current study, we have analyzed the expression and functional role of E-and P-selectin ligands on CD4+ T cells induced in vivo upon skin sensitization, using soluble selectin-Ig chimera and blocking Abs. Only low numbers of CD4+ cells expressing significant levels of E- or P-selectin ligands were present in s.c. lymph nodes of untreated mice (0.5–1.5% and 2–4%, respectively). Induction of a delayed-type hypersensitivity reaction increased the percentage of E-selectin-binding CD4+ cells in the draining lymph nodes up to 6 to 9% and that of P-selectin-binding cells up to 14%. The majority of E- and P-selectin-binding cells displayed an activated phenotype as judged by the increase in IL-2R, CD71, or cell size. The populations of E- and P-selectin-binding cells were largely overlapping; all E-selectin-binding cells also bound to P-selectin, whereas only a subfraction of P-selectin-binding cells reacted with E-selectin. Both E- and P-selectin-binding CD4+ cells, isolated by FACS, efficiently migrated into inflamed, but not normal skin, whereas P- or E-selectin ligand-negative CD4+ T cells did not. Abs against one of the two endothelial selectins partially inhibited the entry of isolated, ligand-positive cells, whereas a combination of Abs against both selectins almost completely abrogated skin homing. These data indicate that the expression of functional ligands for E- and for P-selectin is essential for homing of CD4+ T cells into the inflamed skin.