CD69 regulates type I IFN-induced tolerogenic signals to mucosal CD4 T cells that attenuate their colitogenic potential

CD69 is highly expressed by lymphocytes at mucosal surfaces. We aimed to investigate the role of CD69 in mucosal immune responses. The expression of CD69 by CD4 T cells isolated from the spleen, mesenteric lymph nodes, small intestinal lamina propria, and colonic lamina propria was determined in specific pathogen-free B6 and TCR transgenic animals, as well as in germ-free B6 mice. Transfer colitis was induced by transplanting RAG(-/-) mice with B6 or CD69(-/-)CD45RB(high) CD4 T cells. CD69 expression by CD4 T cells is induced by the intestinal microflora, oral delivery of specific Ag, and type I IFN (IFN-I) signals. CD4 T cells from CD69(-/-) animals produce higher amounts of the proinflammatory cytokines IFN-γ, TNF-α, and IL-21, whereas the production of TGF-β1 is decreased. CD69-deficient CD4 T cells showed reduced potential to differentiate into Foxp3(+) regulatory T cells in vivo and in vitro. The transfer of CD69(-/-)CD45RB(high) CD4 T cells into RAG(-/-) hosts induced an accelerated colitis. Oral tolerance was impaired in CD69(-/-) and IFN-I receptor 1-deficient mice when compared with B6 and OT-II × RAG(-/-) animals. Polyinosinic-polycytidylic acid treatment of RAG(-/-) mice transplanted with B6 but not CD69(-/-) or IFN-I receptor 1-deficient CD45RB(high) CD4 T cells attenuated transfer colitis. CD69 deficiency led to the increased production of proinflammatory cytokines, reduced Foxp3(+) regulatory T cell induction, impaired oral tolerance, and more severe colitis. Hence, the activation Ag CD69 plays an important role in regulating mucosal immune responses.     

The development of colitogenic CD4(+) T cells is regulated by IL-7 in collaboration with NK cell function in a murine model of colitis

We previously reported that IL-7(-/-)RAG(-/-) mice receiving naive T cells failed to induce colitis. Such abrogation of colitis may be associated with not only incomplete T cell maintenance due to the lack of IL-7, but also with the induction of colitogenic CD4(+) T cell apoptosis at an early stage of colitis development. Moreover, NK cells may be associated with the suppression of pathogenic T cells in vivo, and they may induce apoptosis of CD4(+) T cells. To further investigate these roles of NK cells, RAG(-/-) and IL-7(-/-)RAG(-/-) mice that had received naive T cells were depleted of NK cells using anti-asialo GM1 and anti-NK1.1 Abs. NK cell depletion at an early stage, but not at a later stage during colitogenic effector memory T cell (T(EM)) development, resulted in exacerbated colitis in recipient mice even in the absence of IL-7. Increased CD44(+)CD62L(-) T(EM) and unique CD44(-)CD62L(-) T cell subsets were observed in the T cell-reconstituted RAG(-/-) recipients when NK cells were depleted, although Fas, DR5, and IL-7R expressions in this subset differed from those in the CD44(+)CD62L(-) T(EM) subset. NK cell characteristics were the same in the presence or absence of IL-7 in vitro and in vivo. These results suggest that NK cells suppress colitis severity in T cell-reconstituted RAG(-/-) and IL-7(-/-)RAG(-/-) recipient mice through targeting of colitogenic CD4(+)CD44(+)CD62L(-) T(EM) and, possibly, of the newly observed CD4(+)CD44(-)CD62L(-) subset present at the early stage of T cell development.     

MHC-II-independent CD4+ T cells induce colitis in immunodeficient RAG-/- hosts

CD4(+) alpha beta T cells from either normal C57BL/6 (B6) or MHC-II-deficient (A alpha(-/-) or A beta(-/-)) B6 donor mice engrafted into congenic immunodeficient RAG1(-/-) B6 hosts induced an aggressive inflammatory bowel disease (IBD). Furthermore, CD4(+) T cells from CD1d(-/-) knockout (KO) B6 donor mice but not those from MHC-I(-/-) (homozygous transgenic mice deficient for beta(2)-microglobulin) KO B6 mice induced a colitis in RAG(-/-) hosts. Abundant numbers of in vivo activated (CD69(high)CD44(high)CD28(high)) NK1(+) and NK1(-) CD4(+) T cells were isolated from the inflamed colonic lamina propria (cLP) of transplanted mice with IBD that produced large amounts of TNF-alpha and IFN-gamma but low amounts of IL-4 and IL-10. IBD-associated cLP Th1 CD4(+) T cell populations were polyclonal and MHC-II-restricted when derived from normal B6 donor mice, but oligoclonal and apparently MHC-I-restricted when derived from MHC-II-deficient (A alpha(-/-) or A beta(-/-)) B6 donor mice. cLP CD4(+) T cell populations from homozygous transgenic mice deficient for beta(2)-microglobulin KO B6 donor mice engrafted into RAG(-/-) hosts were Th2 and MHC-II restricted. These data indicate that MHC-II-dependent as well as MHC-II-independent CD4(+) T cells can induce a severe and lethal IBD in congenic, immunodeficient hosts, but that the former need the latter to express its IBD-inducing potential.     

T cell-induced inflammation of the small and large intestine in immunodeficient mice

It is well known that transfer of CD4+CD45RBhigh (na?ve) T cells into syngeneic lymphocyte-deficient mice induces chronic colitis. However, no studies have reported the presence of small bowel inflammation in this T cell-dependent model. Therefore, the objective of this study was to evaluate and compare small and large bowel inflammation induced by transfer of na?ve T cells into two different immunodeficient recipient mice. T and B cell-deficient recombinase activating gene 1-deficient [RAG knockout (KO)] and T cell-deficient T cell receptor-beta x T cell receptor-delta double-deficient (TCR KO) mice were reconstituted with wild-type na?ve T cells and observed for signs of disease. We found that reconstituted RAG KO mice developed moderate to severe colitis and inflammation of the entire small intestine at 6-8 wk after T cell transfer. Adoptive transfer of na?ve T cells into TCR KO mice induced a milder form of chronic colitis and small bowel inflammation that was confined primarily to the duodenum at 10-12 wk after T cell transfer. T helper cell 1 and macrophage-derived proinflammatory cytokine mRNA levels correlated well with the localization and severity of the chronic large and small bowel inflammation. In addition, we observed comparable homing and expansion of donor lymphocytes in the gut and secondary lymphoid tissues of both recipients. Taken together, our data demonstrate that transfer of na?ve T cells into immunodeficient recipient mice induces both chronic small and large bowel inflammation and that the presence of B cells in the TCR KO recipients may play a role in regulating chronic intestinal inflammation.     

Over-Expression of CD200 Protects Mice from Dextran Sodium Sulfate Induced Colitis

Background and aim

CD200:CD200 receptor (CD200R) interactions lead to potent immunosuppression and inhibition of autoimmune inflammation. We investigated the effect of "knockout"of CD200 or CD200R, or over-expression of CD200, on susceptibility to dextran sodium sulfate (DSS)—induced colitis, a mouse model of inflammatory bowel disease (IBD).

Methods

Acute or chronic colitis was induced by administration of dextran sodium sulfate (DSS) in four groups of age-matched C57BL/6 female mice: (1) CD200-transgenic mice (CD200^tg); (2) wild-type (WT) mice; (3) CD200 receptor 1-deficient (CD200R1KO) mice; and (4) CD200-deficient (CD200KO) mice. The extent of colitis was determined using a histological scoring system. Colon tissues were collected for quantitative RT-PCR and Immunohistochemical staining. Supernatants from colonic explant cultures and mononuclear cells isolated from colonic tissue were used for ELISA.

Results

CD200KO and CD200R1KO mice showed greater sensitivity to acute colitis than WT mice, with accelerated loss of body weight, significantly higher histological scores, more severe infiltration of macrophages, neutrophils and CD3⁺ cells, and greater expression of macrophage-derived inflammatory cytokines, whose production was inhibited in vitro (in WT/CD200KO mouse cells) by CD200. In contrast, CD200^tg mice showed less sensitivity to DSS compared with WT mice, with attenuation of all of the features seen in other groups. In a chronic colitis model, greater infiltration of Foxp3⁺ regulatory T (Treg) cells was seen in the colon of CD200^tg mice compared to WT mice, and anti-CD25 mAb given to these mice attenuated protection.

Conclusions

The CD200:CD200R axis plays an immunoregulatory role in control of DSS induced colitis in mice.     

Crucial Role for CD69 in the Pathogenesis of Dextran Sulphate Sodium-Induced Colitis

CD69 is a membrane molecule transiently expressed on activated lymphocytes, and its selective expression in inflammatory infiltrates suggests that it plays a role in the pathogenesis of inflammatory diseases. In this study, we used CD69-deficient (CD69 KO) mice to assess the role of CD69 in the pathogenesis of dextran sulphate sodium (DSS)-induced acute and chronic colitis. The severity of colitis was assessed by the survival rate, clinical signs, colon length, histological examination and the expression of cytokines and chemokines in the large intestines. Both acute and chronic colitis were attenuated in the CD69 KO mice, as reflected by the lower lethality, weight loss, clinical signs, and improved histological findings. CD69⁺ cells infiltrated extensively into the inflamed mucosa of the colon in WT mice after DSS treatment. Experiments with the transfer of WT CD4 T cells into CD69 KO mice restored the induction of colitis. The administration of an anti-CD69 antibody also inhibited the induction of the DSS-induced colitis. These results indicate that CD69 expressed on CD4 T cells plays an important role in the pathogenesis of DSS-induced acute and chronic colitis, and that CD69 could be a possible therapeutic target for colitis.     

CD4+ Th1 and CD8+ type 1 cytotoxic T cells both play a crucial role in the full development of contact hypersensitivity

The role of CD4(+) vs CD8(+) T cells in contact hypersensitivity (CHS) remains controversial. In this study, we used gene knockout (KO) mice deficient in CD4(+) or CD8(+) T cells to directly address this issue. Mice lacking either CD4(+) or CD8(+) T cells demonstrated depressed CHS responses to dinitrofluorobenzene and oxazolone compared with wild-type C57BL/6 mice. The depression of CHS was more significant in CD8 KO mice than in CD4 KO mice. Furthermore, in vivo depletion of either CD8(+) T cells from CD4 KO mice or CD4(+) T cells from CD8 KO mice virtually abolished CHS responses. Lymph node cells (LNCs) from hapten-sensitized CD4 and CD8 KO mice showed a decreased capacity for transferring CHS. In vitro depletion of either CD4(+) T cells from CD8 KO LNCs or CD8(+) T cells from CD4 KO LNCs resulted in a complete loss of CHS transfer. LNCs from CD4 and CD8 KO mice produced significant amounts of IFN-gamma, indicating that both CD4(+) and CD8(+) T cells are able to secrete IFN-gamma. LNCs from CD8, but not CD4, KO mice were able to produce IL-4 and IL-10, suggesting that IL-4 and IL-10 are mainly derived from CD4(+) T cells. Intracellular cytokine staining of LNCs confirmed that IFN-gamma-positive cells consisted of CD4(+) (Th1) and CD8(+) (type 1 cytotoxic T) T cells, whereas IL-10-positive cells were exclusively CD4(+) (Th2) T cells. Collectively, these results suggest that both CD4(+) Th1 and CD8(+) type 1 cytotoxic T cells are crucial effector cells in CHS responses to dinitrofluorobenzene and oxazolone in C57BL/6 mice.     

Cutting edge: CD4+CD25+ regulatory T cells impaired for intestinal homing can prevent colitis

Transfer of CD4(+)CD45RB(high) T cells into RAG(-/-) mice causes colitis, which can be prevented by CD4(+)CD25(+) regulatory T cells (Treg). Colitis induction by CD4(+)CD45RB(high) T cells requires beta(7) integrin-dependent intestinal localization, but the importance of beta(7) integrins for Treg function is unknown. In this study, we show that beta(7)(-/-) Treg were effective in preventing colitis. Treg expanded in vivo to the same extent as CD4(+)CD45RB(high) T cells after transfer and they did not inhibit CD4(+)CD45RB(high) T cell expansion in lymphoid tissues, although they prevented the accumulation of Th1 effector cells in the intestine. beta(7)(-/-) Treg were significantly reduced in the large intestine, however, compared with wild-type Treg, and regulatory activity could not be recovered from the intestine of recipients of beta(7)(-/-) Treg. These data demonstrate that Treg can prevent colitis by inhibiting the accumulation of tissue-seeking effector cells and that Treg accumulation in the intestine is dispensable for colitis suppression.     

Functional role of P-selectin glycoprotein ligand 1/P-selectin interaction in the generation of tolerogenic dendritic cells

Dendritic cells (DCs) have a key role in both the generation of the immune response and the induction of tolerance to self-Ags. In this work, the possible role of P-selectin glycoprotein ligand 1 (PSGL-1) on the tolerogenic activity of human DCs was explored. We found that the engagement of PSGL-1 by P-selectin on DCs induced the expression of c-Fos, IDO, IL-10, and TGF-beta genes. Remarkably, stimulation of DCs through PSGL-1 with P-selectin enhanced their capability to generate CD4(+)CD25(+)Foxp3(+) regulatory T cells, which expressed high levels of TGF-beta1 mRNA, synthesized IL-10, and suppressed the proliferation of autologous CD4(+)CD25(-) T cells. Accordingly, we found that DCs from PSGL-1(-/-) mice expressed higher levels of MHC class II molecules, and exhibited an enhanced immunogenicity compared with wild-type mice. In addition, the percentage of CD4(+)CD25(+)Foxp3(+) regulatory T cells in the thymus of PSGL-1-deficient animals was significantly reduced. Our data reveal an unexpected role of PSGL-1 on the tolerogenic function of DCs, and the regulation of the immune response.     

CD43 collaborates with P-selectin glycoprotein ligand-1 to mediate E-selectin-dependent T cell migration into inflamed skin

Activated T cell migration into nonlymphoid tissues is initiated by the interactions of P- and E-selectin expressed on endothelial cells and their ligands on T cells. P-selectin glycoprotein ligand-1 (PSGL-1) has been the only E-selectin ligand demonstrated to function during the in vivo migration of activated T cells. We show in this study that CD43-deficient Th1 cells, like PSGL-1-deficient cells, exhibited reduced E-selectin-binding activity compared with wild-type cells. Th1 cells with a PSGL-1 and CD43 double deficiency showed even less E-selectin-binding activity. In migration assays in which adoptively transferred cells migrate to inflamed skin P- and E-selectin dependently, CD43 contributed significantly to PSGL-1-independent Th1 cell migration. In addition, in vivo activated T cells from the draining lymph nodes of sensitized mice deficient in PSGL-1 and/or CD43 showed significantly decreased E-selectin-binding activity and migration efficiency, with T cells from double-deficient mice showing the most profound decrease. Collectively, these results demonstrate that the CD43 expressed on activated T cells functions as an E-selectin ligand and thereby mediates T cell migration to inflamed sites, in collaboration with PSGL-1.     

PSGL-1 regulates the migration and proliferation of CD8(+) T cells under homeostatic conditions

P-selectin glycoprotein ligand-1 (PSGL-1), a heavily glycosylated sialomucin expressed on most leukocytes, has dual function as a selectin ligand for leukocyte rolling on vascular selectins expressed in inflammation and as a facilitator of resting T cell homing into lymphoid organs. In this article, we document disturbances in T cell homeostasis present in PSGL-1(null) mice. Naive CD4(+) and CD8(+) T cell frequencies were profoundly reduced in blood, whereas T cell numbers in lymph nodes and spleen were at or near normal levels. Although PSGL-1(null) T cells were less efficient at entering lymph nodes, they also remained in lymph nodes longer than PSGL-1(+/+) T cells, suggesting that PSGL-1 supports T cell egress. In addition, PSGL-1(null) CD8(+) T cell proliferation was observed under steady-state conditions and PSGL-1(null) CD8(+) T cells were found to be hyperresponsive to homeostatic cytokines IL-2, IL-4, and IL-15. Despite these disturbances in T cell homeostasis, PSGL-1(null) mice exhibited a normal acute response (day 8) to lymphocytic choriomeningitis virus infection but generated an increased frequency of memory T cells (day 40). Our observations demonstrate a novel pleiotropic influence of PSGL-1 deficiency on several aspects of T cell homeostasis that would not have been anticipated based on the mild phenotype of PSGL-1(null) mice. These potentially offsetting effects presumably account for the near-normal cellularity seen in lymph nodes of PSGL-1(null) mice.     

IL-7 exacerbates chronic colitis with expansion of memory IL-7Rhigh CD4+ mucosal T cells in mice

We have previously demonstrated that mucosal CD4(+) T cells expressing high levels of IL-7 receptor (IL-7R(high)) are pathogenic cells responsible for chronic colitis. Here we investigate whether IL-7 is directly involved in the expansion of IL-7R(high) memory CD4(+) mucosal T cells and the exacerbation of colitis. We first showed that CD4(+) lamina propria lymphocytes (LPLs) from wild-type, T cell receptor-alpha-deficient (TCR-alpha(-/-)), and recombinase-activating gene (RAG)-2(-/-)-transferred mice with or without colitis showed phenotypes of memory cells, but only CD4(+) LPLs from colitic mice showed IL-7R(high). In vitro stimulation by IL-7, but not by IL-15 and thymic stromal lymphopoietin, enhanced significant proliferative responses and survival of colitic CD4(+), but not normal CD4(+) LPLs. Importantly, in vivo administration of IL-7 mice accelerated the expansion of IL-7R(high) memory CD4(+) LPLs and thereby exacerbated chronic colitis in RAG-2(-/-) mice transferred with CD4(+) LPLs from colitic TCR-alpha(-/-) mice. Conversely, the administration of anti-IL-7R monoclonal antibody significantly inhibited the development of TCR-alpha(-/-) colitis with decreased expansion of CD4(+) LPLs. Collectively, the present data indicate that IL-7 is essential for the expansion of pathogenic memory CD4(+) T cells under pathological conditions. Therefore, therapeutic approaches targeting the IL-7R pathway may be feasible in the treatment of human inflammatory bowel disease.     

CD31 is required on CD4+ T cells to promote T cell survival during Salmonella infection

Hematopoietic cells constitutively express CD31/PECAM1, a signaling adhesion receptor associated with controlling responses to inflammatory stimuli. Although expressed on CD4(+) T cells, its function on these cells is unclear. To address this, we have used a model of systemic Salmonella infection that induces high levels of T cell activation and depends on CD4(+) T cells for resolution. Infection of CD31-deficient (CD31KO) mice demonstrates that these mice fail to control infection effectively. During infection, CD31KO mice have diminished numbers of total CD4(+) T cells and IFN-γ-secreting Th1 cells. This is despite a higher proportion of CD31KO CD4(+) T cells exhibiting an activated phenotype and an undiminished capacity to prime normally and polarize to Th1. Reduced numbers of T cells reflected the increased propensity of naive and activated CD31KO T cells to undergo apoptosis postinfection compared with wild-type T cells. Using adoptive transfer experiments, we show that loss of CD31 on CD4(+) T cells alone is sufficient to account for the defective CD31KO T cell accumulation. These data are consistent with CD31 helping to control T cell activation, because in its absence, T cells have a greater propensity to become activated, resulting in increased susceptibility to become apoptotic. The impact of CD31 loss on T cell homeostasis becomes most pronounced during severe, inflammatory, and immunological stresses such as those caused by systemic Salmonella infection. This identifies a novel role for CD31 in regulating CD4 T cell homeostasis.     

Absence of allograft ICAM-1 attenuates alloantigen-specific T cell priming,but not primed T cell trafficking into the graft,to mediate acute rejection

The expression and function of ICAM-1 are critical components in the initiation and elicitation of many T cell-mediated responses. Whether ICAM-1 expression is required on the T cells or on the APC during T cell priming remains unclear. To address this issue in alloantigen-specific T cell activation, the priming and function of T cells in response to heart allografts from MHC-mismatched wild-type vs ICAM-1(-/-) donors were tested. Wild-type C57BL/6 (H-2(b)) heart allografts were rejected by A/J (H-2(a)) recipients on days 7-9, whereas B6.ICAM-1(-/-) allografts survived until days 18-23 post-transplant. On day 7 post-transplant, infiltrating macrophages and CD4(+) and CD8(+) T cells in the ICAM-1(-/-) allografts were 20-30% those observed in the wild-type allografts. ELISPOT analyses indicated that the number of alloantigen-specific T cells producing IFN-gamma from recipients of ICAM-1-deficient grafts was 60% lower than that from recipients of wild-type allografts. On day 16 post-transplant, these numbers did not markedly increase in ICAM-1-deficient allograft recipients. Consistent with the reduced priming of alloreactive T cells, isolated dendritic cells from ICAM-1(-/-) mice stimulated allogeneic T cell proliferation poorly compared with wild-type dendritic cells. When A/J mice were primed with wild-type dendritic cells and then received wild-type or ICAM-1-deficient heart allografts 3 days later, the primed recipients rejected the wild-type and ICAM-1(-/-) allografts on days 5-6 post-transplant. These results indicate that optimal priming of alloreactive T cells requires allograft expression of ICAM-1, but, once primed, recipient T cell infiltration into the allograft is independent of graft ICAM-1 expression.     

Increased T cell autoreactivity in the absence of CD40-CD40 ligand interactions: a role of CD40 in regulatory T cell development

Mutations in the CD40 ligand (CD40L) gene lead to X-linked immunodeficiency with hyper-IgM, which is often associated with autoimmune diseases. To determine the contribution of defective CD40-CD40L interactions to T cell autoreactivity, we reconstituted CD40-CD40L interactions by transferring T cells from CD40-deficient mice to syngenic athymic nude mice and assessed autoimmunity. T cells from CD40-deficient mice triggered autoimmune diseases accompanied with elevations of various autoantibodies, while those from wild-type mice did not. In CD40-deficient mice, the CD25(+) CD45RB(low) CD4(+) subpopulation which regulates T cell autoreactivity was markedly reduced. CD40-deficient APCs failed to induce T regulatory cells 1 producing high levels of an inhibitory cytokine, IL-10 in vitro. Furthermore, autoimmune development was inhibited when T cells from CD40-deficient mice were cotransferred with CD45RB(low) CD4(+) T cells from wild-type mice or with T regulatory cells 1 induced on CD40-expressing APCs. Collectively, our results indicate that CD40-CD40L interactions contribute to negative regulation of T cell autoreactivity and that defective interactions can lead to autoimmunity.     

Exacerbated susceptibility to infection-stimulated immunopathology in CD1d-deficient mice

Mice lacking functional CD1d genes were used to study mechanisms of resistance to the protozoan parasite Toxoplasma gondii. Wild-type (WT) BALB/c mice, CD1d-deficient BALB/c mice, and WT C57BL/6 mice all survived an acute oral infection with a low dose of mildly virulent strain ME49 T. gondii cysts. In contrast, most CD1d-deficient C57BL/6 mice died within 2 wk of infection. Despite having parasite burdens that were only slightly higher than WT mice, CD1d-deficient C57BL/6 mice displayed greater weight loss and intestinal pathology. In C57BL/6 mice, CD4(+) cells can cause intestinal pathology during T. gondii infection. Compared with WT mice, infected CD1d-deficient C57BL/6 mice had higher frequencies and numbers of activated (CD44(high)) CD4(+) cells in mesenteric lymph nodes. Depletion of CD4(+) cells from CD1d-deficient mice reduced weight loss and prolonged survival, demonstrating a functional role for CD4(+) cells in their increased susceptibility to T. gondii infection. CD1d-deficient mice are deficient in Valpha14(+) T cells, a major population of NKT cells. Involvement of these cells in resistance to T. gondii was investigated using gene-targeted Jalpha18-deficient C57BL/6 mice, which are deficient in Valpha14(+) T cells. These mice did not succumb to acute infection, but experienced greater weight loss and more deaths than B6 mice during chronic infection, indicating that Valpha14(+) cells contribute to resistance to T. gondii. The data identify CD4(+) cells as a significant component of the marked susceptibility to T. gondii infection observed in CD1d-deficient C57BL/6 mice, and establish T. gondii as a valuable tool for deciphering CD1d-dependent protective mechanisms.     

Intercellular adhesion molecule 1 deficiency leads to impaired recruitment of T lymphocytes and enhanced host susceptibility to infection with Trypanosoma cruzi

In this study, we investigated the involvement of Th1 cytokines in the expression of cell adhesion molecules (CAM) and recruitment of inflammatory cells to the heart of mice infected with Trypanosoma cruzi. Our results show that endogenously produced IFN-gamma is essential to induce optimal expression of VCAM-1 and ICAM-1 on the cardiac vascular endothelium of infected mice. Furthermore, the influx of inflammatory cells into the cardiac tissue was impaired in Th1 cytokine-deficient infected mice, paralleling the intensity of VCAM-1 and ICAM-1 expression on the vascular endothelium. Consistent with the importance of ICAM-1 in host resistance, ICAM-1 knockout (KO) mice were highly susceptible to T. cruzi infection, as assessed by mortality rate, parasitemia, and heart tissue parasitism. The enhanced parasitism was associated with a decrease in the numbers of CD4(+) and CD8(+) T lymphocytes in the heart tissue of ICAM-1 KO mice. Additionally, ICAM-1 KO mice mounted an unimpaired IFN-gamma response and IFN-gamma-dependent production of reactive nitrogen intermediates and parasite- specific IgG2a. Supporting the participation of ICAM-1 in cell migration during T. cruzi infection, the entrance of adoptively transferred PBL from T. cruzi-infected wild-type C57BL/6 mice into the cardiac tissue of ICAM-1 KO mice was significantly abrogated. Therefore, we favor the hypothesis that ICAM-1 plays a crucial role in T lymphocyte recruitment to the cardiac tissue and host susceptibility during T. cruzi infection.     

Cytokine-induced alterations of α7 nicotinic receptor in colonic CD4 T cells mediate dichotomous response to nicotine in murine models of Th1/Th17- versus Th2-mediated colitis

Ulcerative colitis (UC) and Crohn's disease (CD) are two forms of chronic inflammatory bowel disease. CD4 T cells play a central role in the pathogenesis of both diseases. Smoking affects both UC and CD but with opposite effects, ameliorating UC and worsening CD. We hypothesized that the severity of gut inflammation could be modulated through T cell nicotinic acetylcholine receptors (nAChRs) and that the exact clinical outcome would depend on the repertoire of nAChRs on CD4 T cells mediating each form of colitis. We measured clinical and immunologic outcomes of treating BALB/c mice with oxazolone- and trinitrobenzene sulfonic acid (TNBS)-induced colitides by nicotine. Nicotine attenuated oxazolone colitis, which was associated with an increased percentage of colonic regulatory T cells and a reduction of Th17 cells. TCR stimulation of naive CD4(+)CD62L(+) T cells in the presence of nicotine upregulated expression of Foxp3. In marked contrast, nicotine worsened TNBS colitis, and this was associated with increased Th17 cells among colonic CD4 T cells. Nicotine upregulated IL-10 and inhibited IL-17 production, which could be abolished by exogenous IL-12 that also abolished the nicotine-dependent upregulation of regulatory T cells. The dichotomous action of nicotine resulted from the up- and downregulation of anti-inflammatory α7 nAChR on colonic CD4 T cells induced by cytokines characteristic of the inflammatory milieu in oxazolone (IL-4) and TNBS (IL-12) colitis, respectively. These findings help explain the dichotomous effect of smoking in patients with UC and CD, and they underscore the potential for nicotinergic drugs in regulating colonic inflammation.