Urinary neopterin is a valuable tool in monitoring Crohn's disease activity

BACKGROUND

The aim was to investigate the relation between urinary neopterin and the Crohn's Disease Activity Index (CDAI) and to compare its ability to discriminate active versus inactive CD with serum C-reactive protein (CRP).

METHODS

In all, 217 urinary samples for neopterin measurement were obtained in a cohort of 93 consecutive patients with CD and 66 samples in 33 healthy volunteers. Clinical parameters were recorded and blood samples for CRP were collected as well.

RESULTS

Whereas patients with inactive CD showed similar levels of urinary neopterin excretion than healthy volunteers (163 +/- 8 versus 142 +/- 7 nmol/mol of creatinine, respectively; P = 0.1), urinary neopterin excretion from mild to severe active CD was significantly higher (302 +/- 15 nmol/mol of creatinine; P < 0.001). Serum CRP levels were higher in active CD (14.8 +/- 2.1 mg/L) compared with inactive CD (5.6 +/- 0.8 mg/L; P < 0.001). Urinary neopterin excretion, and to a lesser degree CRP, were positively and significantly correlated with CDAI (r = 0.64 and 0.43, respectively, P < 0.001). Based on the cutoff of 183 nmol/mol of creatinine for urinary neopterin, the sensitivity and specificity of urinary neopterin to discriminate between active and inactive CD were 73% and 82%, respectively, and the positive and negative predictive values were 80% and 78%, respectively.

CONCLUSIONS

Urinary neopterin excretion is an objective, valuable, simple, and noninvasive biomarker to detect and follow fluctuations of CD activity. Further work is warranted to study its clinical value and relation to mucosal healing.

Oral tolerance and regulation of mucosal immunity

Regulated mechanisms sustain the ability of the gut immune system to discriminate harmless food antigens (Ag) and commensal bacteria from pathogenic microorganisms, resulting in tolerance versus protective immunity, respectively. Antigens of the gut commensals are not simply ignored, but rather trigger an active immunosuppressive process, more commonly known as oral tolerance, which prevents the outcome of immunopathology. Both intrinsic properties of the gut microenvironment and cellular actors, as well as peripheral events induced by systemic dissemination of oral Ag, promote the induction of regulatory mechanisms that ensure maintenance of gut homeostasis. The aim of this review is to provide a synthetic update on the mechanisms of oral tolerance, with particular emphasis on the complex interplay between regulatory CD4+ T cells, dendritic cells and the gut microenvironment.

Afferent and efferent phases of allergic contact dermatitis (ACD) can be induced after a single skin contact with haptens: evidence using a mouse model of primary ACD

Allergic contact dermatitis is a T cell-mediated delayed type hypersensitivity reaction that occurs upon hapten challenge in sensitized individuals. The inflammatory response in classical allergic contact dermatitis requires both a sensitization phase and an elicitation phase responsible for the recruitment and activation of specific T cells at the site of hapten skin challenge. Conversely, previously unsensitized patients may develop a "primary allergic contact dermatitis" after the first skin contact with potent contact sensitizers leading to a skin inflammation with all the features of classical allergic contact dermatitis. In this study we used an experimental murine model, referred to as contact hypersensitivity, to study the pathophysiology of primary allergic contact dermatitis and its relationship to classical allergic contact dermatitis. We show that one epicutaneous application of a nonirritant dose of hapten (2,4-dini-trofluorobenzene, fluorescein isothiocyanate) was sufficient to induce an optimal allergic contact dermatitis reaction at the site of primary contact with the hapten without subsequent challenge. As in classical allergic contact dermatitis, the skin inflammation in primary allergic contact dermatitis was mediated by interferon-gamma producing, CD8+ effector T cells that were induced in the draining lymph nodes at day 5 postsensitization and downregulated by CD4+ T cells. Reverse transcription-polymerase chain reaction analysis revealed that the primary allergic contact dermatitis reaction was mediated by a recruitment of CD8+ T cells at the sensitization skin site at day 6 postsensitization. Analysis of the fate of the hapten fluorescein isothiocyanate applied once on the skin revealed its persistence in the epidermis for up to 14 d after skin painting. These results suggest that the development of primary allergic contact dermatitis (i.e., without secondary challenge) is associated with persistence of the hapten in the skin, which allows the recruitment and activation of CD8+ T cells at the site of the single hapten application.

Measles virus exploits dendritic cells to suppress CD4+ T-cell proliferation via expression of surface viral glycoproteins independently of T-cell trans-infection

Dendritic cells (DC) have been proposed to play a pivotal role in transient immune suppression induced by measles virus (MV) infection. In the present study, we show that DC-induced suppression of T-cell proliferation was not mediated by IL-10 or IFNalpha/beta, which are released following infection of DC, but required cell contacts between MV-infected DC and T cells. Human sera containing neutralizing anti-MV antibodies, as well as anti-MV hemagglutinin (HA) or fusion protein (F) mAbs, were found (i) to reverse suppression and (ii) to restore DC allostimulatory capacity. Interestingly, DC-induced T-cell suppression was associated with both phenotypic and functional DC maturation, as demonstrated by IL-12 production and chemotaxis to MIP-3beta. These data suggest that MV infection turns on the maturation program of DC allowing migration to draining lymph nodes, where potent T-cell immune suppression might be achieved via cell surface expression of HA and F glycoproteins, independently of T cell trans-infection.

Flagellin stimulation of intestinal epithelial cells triggers CCL20-mediated migration of dendritic cells

Enteropathogenic bacteria elicit mucosal innate and adaptive immune responses. We investigated whether gut epithelial cells played a role in triggering an adaptive immune response by recruiting dendritic cells (DCs). Immature DCs are selectively attracted by the CCL20 chemokine. The expression of the CCL20 gene in human intestinal epithelial cell lines was up-regulated by pathogenic bacteria, including Salmonella species, but not by indigenous bacteria of the intestinal flora. The Salmonella machinery for epithelial cell invasion was not required for CCL20 gene activation. Flagellin but not the lipopolysaccharide was found to be the Salmonella factor responsible for stimulation of epithelial CCL20 production. CCL20 in turn triggered a specific migration of immature DCs. Our data show that crosstalk between bacterial flagellin and epithelial cells is essential for the recruitment of DCs, a mechanism that could be instrumental to initiate adaptive immune responses in the gut.

Dendritic cells and viral immunity: friends or foes?

Dendritic cells (DC) residing in epithelial tissues of various mucosae and the skin are characterized by the unique ability to capture antigens and migrate to draining lymph nodes, where they can activate naive and memory T cells. Although DC play a pivotal role in inducing protective immunity to viral infection, they can also be exploited by viruses to evade the host immune response, induce immune suppression, or serve as latent viral reservoirs. Thus, virus interactions with DC may lead to an immune response that can be protective, but does not necessarily lead to complete virus elimination, resulting in immunopathology.

Dendritic cells recruitment and in vivo priming of CD8+ CTL induced by a single topical or transepithelial immunization via the buccal mucosa with measles virus nucleoprotein

The buccal mucosa, a prototype of pluristratified mucosal epithelia, contains a network of directly accessible class II(+) epithelial dendritic cells (DC), similar to skin Langerhans cells. We showed that a single buccal immunization with measles virus nucleoprotein (NP), by either topical application onto or intradermal injection in the buccal mucosa, induced in vivo priming of protective class I-restricted specific CD8(+) CTL. Both routes of immunization with NP induced a rapid recruitment of DC into the mucosa, which peaked at 2 h and decreased by 24 h. Treatment of mice with Flt3 ligand resulted in an increased number of DC in the buccal mucosa and enhanced the frequency of IFN-gamma-producing NP-specific effectors and the NP-specific CTL response generated after buccal immunization with NP. Finally, NP-pulsed bone marrow-derived DC induced NP-specific IFN-gamma-producing cells upon adoptive transfer to naive mice. These data demonstrate that a viral protein delivered to DC of the buccal mucosa induces in vivo priming of protective anti-viral CD8(+) CTL.

Combined natural killer cell and dendritic cell functional deficiency in KARAP/DAP12 loss-of-function mutant mice

KARAP/DAP12 is a transmembrane polypeptide with an intracytoplasmic immunoreceptor tyrosine-based activation motif (ITAM). KARAP/DAP12 is associated with several activating cell surface receptors in hematopoietic cells. Here, we report that knockin mice bearing a nonfunctional KARAP/DAP12 ITAM present altered innate immune responses. Although in these mice NK cells are present and their repertoire of inhibitory MHC class I receptors is intact, the NK cell spectrum of natural cytotoxicity toward tumor cell targets is restricted. KARAP/DAP12 loss-of-function mutant mice also exhibit a dramatic accumulation of dendritic cells in muco-cutaneous epithelia, associated with an impaired hapten-specific contact sensitivity. Thus, despite its homology with CD3zeta and FcRgamma, KARAP/DAP12 plays a specific role in innate immunity, emphasizing the nonredundancy of these ITAM-bearing polypeptides in hematopoietic cells.

Development of minimal lentivirus vectors derived from simian immunodeficiency virus (SIVmac251) and their use for gene transfer into human dendritic cells

Lentivirus-derived vectors are very promising gene delivery systems since they are able to transduce nonproliferating differentiated cells, while murine leukemia virus-based vectors can only transduce cycling cells. Here we report the construction and characterization of highly efficient minimal vectors derived from simian immunodeficiency virus (SIVmac251). High-fidelity PCR amplification of DNA fragments was used to generate a minimal SIV vector formed from a 5' cytomegalovirus early promoter, the 5' viral sequences up to the 5' end of gag required for reverse transcription and packaging, the Rev-responsive element, a gene-expressing cassette, and the 3' long terminal repeat (LTR). Production of SIV vector particles was achieved by transfecting 293T cells with the vector DNA and helper constructs coding for the viral genes and the vesicular stomatitis virus glycoprotein G envelope. These SIV vectors were found to have transducing titers reaching 10(7) transducing units/ml on HeLa cells and to deliver a gene without transfer of helper functions to target cells. The central polypurine tract can be included in the minimal vector, resulting in a two- to threefold increase in the transduction titers on dividing or growth-arrested cells. Based on this minimal SIV vector, a sin vector was designed by deleting 151 nucleotides in the 3' LTR U3 region, and this SIV sin vector retained high transduction titers. Furthermore, the minimal SIV vector was efficient at transducing terminally differentiated human CD34(+) cell-derived or monocyte-derived dendritic cells (DCs). Results show that up to 40% of human primary DCs can be transduced by the SIV vectors. This opens a new perspective in the field of immunotherapy.

Oral administration of hapten inhibits in vivo induction of specific cytotoxic CD8+ T cells mediating tissue inflammation: a role for regulatory CD4+ T cells

We investigated whether oral tolerance could block the development of an inflammatory response mediated by CD8+ T cells, using a mouse model of oral tolerance of contact sensitivity (CS) to the hapten 2, 4-dinitrofluorobenzene (DNFB). In this system, the skin inflammatory response is initiated by hapten-specific class I-restricted cytotoxic CD8+ T (CTL) cells, independently of CD4 help. Oral delivery of DNFB before skin sensitization blocked the CS response by impairing the development of DNFB-specific CD8+ effector T cells in secondary lymphoid organs. This was shown by complete inhibition of DNFB-specific CTL and proliferative responses of CD8+ T cells, lack of specific IFN-gamma-producing CD8+ T cells, and inability of CD8+ T cells to transfer CS in RAG20/0 mice. RT-PCR and immunohistochemical analysis confirmed that recruitment of CD8+ effectors of CS in the skin at the site of hapten challenge was impaired in orally tolerized mice. Sequential anti-CD4 Ab treatment showed that only depletion of CD4+ T cells during the afferent phase of CS abrogated oral tolerance induction by restoring high numbers of specific CD8+ effectors in lymphoid organs, whereas CD4 depletion during the efferent phase of CS did not affect oral tolerance. These data demonstrate that a single intragastric administration of hapten can block in vivo induction of DNFB-specific CD8+ CTL responsible for tissue inflammation and that a subset of regulatory CD4+ T cells mediate oral tolerance by inhibiting expansion of specific CD8+ effectors in lymph nodes.

Modulation of antigen trafficking to MHC class II-positive late endosomes of enterocytes

BACKGROUND & AIMS

Oral tolerance is recognized as a central immunoregulatory phenomenon. The mechanisms of its induction remain unclear, and the role of the intestinal epithelial cells that are able to present antigens to T lymphocytes is poorly understood. In this report, we analyze under in vivo conditions the intracellular targeting of mucosally administered ovalbumin (OVA) to major histocompatibility complex (MHC) class II antigen containing compartments of enterocytes and compare these pathways between BALB/c and SCID mice, the latter being unable to generate a transferable tolerogenic moiety after a feed of OVA.

METHODS

OVA, lysosome-associated membrane proteins (LAMP-1), and MHC class II antigens were localized in jejunal biopsy specimens of BALB/c and SCID mice at 0, 5, 10, 20, 40, 60, and 120 minutes after a single feed with OVA by fluorescence and electron microscopy.

RESULTS

Ten minutes after oral administration, OVA was transported to the proximity of MHC class II antigens within LAMP-1-positive vacuoles and to the basolateral membrane of enterocytes from BALB/c strain mice. However, in SCID mice, OVA reached the paracellular spaces during the same time period through LAMP-1-negative vacuoles of enterocytes, which lacked MHC class II antigens.

CONCLUSIONS

Orally administered OVA is rapidly targeted to late endosomes containing LAMP-1 and MHC class II antigens in enterocytes of BALB/c mice but not in SCID mice bred on a BALB/c background. We suggest that this targeting process within the enterocytes is one of the requirements for the induction of oral tolerance.

Entry sites for oral vaccines and drugs: A role for M cells, enterocytes and dendritic cells?

M cells have long been considered as the unique entry site of macromolecules and pathogens in the intestine, allowing delivery to antigen-presenting cells in the Peyer's patches. Therefore, antigen formulation for the development of oral vaccines has been based on administration of antigens in the form of live replicating pathogens or soluble antigen vectorized into biodegradable microspheres. However, progress in the understanding of the biology of dendritic cells, as well as identification of their localization at different sites of the intestine, suggest that they may capture antigen directly from the lumen of mucosal tissues or from epithelial cells of the intestine. Besides, a role for the absorptive epithelium in antigen presentation through both classical or non-classical MHC elements suggests that PP may not be the exclusive inductive site of the immune response in the gut. Thus, depending on the nature of the antigen (soluble or infectious) there may be different sites of antigen entry through the intestine, and each site may have distinct efficiency to promote a protective immune response, depending on the presence and function of dendritic cells. Cross talk between M cells, epithelial cells and dendritic cells may play an important role in determining the outcome of tolerance versus immunity.

Epicutaneous and transcutaneous immunization using DNA or proteins

Mucocutaneous surfaces are constantly exposed to an array of exogenous antigens including environmental proteins, peptides and low molecular weight and microbial pathogens. These tissues are covered by an epithelium which exerts both the role of a barrier, limiting the penetration of microbes and of hydrophylic antigenic moieties, but at the same time ensures that antigens which penetrate through the epithelium are rapidly captured and transported to draining lymph nodes for initiation of a specific immune response. Epithelial dendritic cells represent the immunocompetent cells responsible for the dynamic uptake and presentation of antigen entering peripheral tissues, and are unique in their efficiency in triggering the immune system and in initiating a primary immune response.

Cytotoxicity is mandatory for CD8(+) T cell-mediated contact hypersensitivity

Contact hypersensitivity (CHS) is a T cell-mediated skin inflammation induced by epicutaneous exposure to haptens in sensitized individuals. We have previously reported that CHS to dinitrofluorobenzene in mice is mediated by major histocompatibility complex (MHC) class I-restricted CD8(+) T cells. In this study, we show that CD8(+) T cells mediate the skin inflammation through their cytotoxic activity. The contribution of specific cytotoxic T lymphocytes (CTLs) to the CHS reaction was examined both in vivo and in vitro, using mice deficient in perforin and/or Fas/Fas ligand (FasL) pathways involved in cytotoxicity. Mice double deficient in perforin and FasL were able to develop hapten-specific CD8(+) T cells in the lymphoid organs but did not show CHS reaction. However, they did not generate hapten-specific CTLs, demonstrating that the CHS reaction is dependent on cytotoxic activity. In contrast, Fas-deficient lpr mice, FasL-deficient gld mice, and perforin-deficient mice developed a normal CHS reaction and were able to generate hapten-specific CTLs, suggesting that CHS requires either the Fas/FasL or the perforin pathway. This was confirmed by in vitro studies showing that the hapten-specific CTL activity was exclusively mediated by MHC class I-restricted CD8(+) T cells which could use either the perforin or the Fas/FasL pathway for their lytic activity. Thus, cytotoxic CD8(+) T cells, commonly implicated in the host defence against tumors and viral infections, could also mediate harmful delayed-type hypersensitivity reactions.

The murine buccal mucosa is an inductive site for priming class I-restricted CD8+ effector T cells in vivo

The present study shows that Langerhans cells of the buccal mucosa and the skin share a similar phenotype, including in situ expression of MHC class II, the mannose receptor DEC-205 and CD11c, and absence of the costimulatory molecules B7.1, B7.2 and CD40 as well as Fas. Application of 2,4-dinitrofluorobenzene (DNFB) onto the buccal mucosa is associated with a rapid migration of dendritic cells (DC) to the epithelium and induction of B7.2 expression on some DC. Buccal sensitization with DNFB elicited a specific contact sensitivity (CS) in response to skin challenge, mediated by class I-restricted CD8+ effector T cells and down-regulated by class II-restricted CD4+ T cells, demonstrated by the lack of priming of class I-deficient mice and the enhanced response of class II-deficient mice, respectively. CS induced by buccal immunization is associated with priming of class I-restricted CD8+ effector T cells endowed with hapten-specific cytotoxic activity. Thus, the buccal epithelium is an inductive site, equivalent to the epidermis, for the generation of CS independent of CD4 help, and of cytotoxic T lymphocyte (CTL) responses mediated by class I-restricted CD8+ T cells. We propose that immunization through the buccal mucosa, which allows antigen presentation by epithelial DC efficient for priming systemic class I-restricted CD8+ CTL, may be a valuable approach for single-dose mucosal vaccination with subunit vaccines.

Langerhans cells are susceptible to measles virus infection and actively suppress T cell proliferation

We have previously reported that the measles virus (MV) could productively infect human dendritic cells (DC), derived in vitro from CD34+ cord blood progenitors in the presence of GM-CSF and TNF-alpha. In this study, we provide evidence that freshly isolated Langerhans cells (LC), which are immature dendritic cells located in skin and mucosal epithelia, are susceptible to MV infection in vitro as assessed by viral antigen expression by both LC syncytia and LC remaining as single cells. Moreover, MV-infected LC completely block naive allogeneic CD4+ T cell proliferation in response to uninfected LC. This active inhibitory effect is not due to virus transmission from infected LC, is independent of the maturation stage of LC at the time of infection and is antigen non-specific and MHC-unrestricted. Thus, both immature and mature LC are susceptible to measles virus infection, which turns these efficient antigen-presenting cells into active tolerogenic cells. LC infection may explain the long lasting immune suppression observed during natural measles infection.

Dual role of dendritic cells in the induction and down-regulation of antigen-specific cutaneous inflammation

We have previously reported that contact sensitivity (CS) to dinitrofluorobenzene (DNFB) in C57BL/6 mice was mediated by MHC class I-restricted CD8+ T cells and down-regulated by MHC class II-restricted CD4+ T cells. In this study, we analyzed the contribution of dendritic cells (DC) in the induction of these two T cell subsets endowed with opposite functions. Hapten-pulsed skin- and bone marrow-derived DC, obtained from either normal C57BL/6 mice or from MHC class II (I+ II-) and MHC class I (I- II+)-deficient mice, were tested for their ability to prime normal mice for CS to dinitrofluorobenzene. Expression of MHC class I molecules by transferred DC was mandatory both for the induction of CS and for the generation of hapten-specific CD8+ T cells in lymphoid organs. I+ II- DC were as potent as I+ II+ DC in priming for CS, demonstrating that activation of effector CD8+ T cells can occur independently of CD4+ T cell help. I- II+ DC could not immunize for CS, although they could sensitize for a delayed-type hypersensitivity reaction to protein Ags. Moreover, I- II+ DC injected simultaneously with cutaneous sensitization down-regulated the inflammatory response, suggesting that hapten presentation by MHC class II molecules could prime regulatory CD4+ T cells. These results indicate that DC can present haptenated peptides by both MHC class I and class II molecules and activate Ag-specific CD8+ effector and CD4+ regulatory T cell subsets, concurrently and independently.

Measles virus infects human dendritic cells and blocks their allostimulatory properties for CD4+ T cells

Measles causes a profound immune suppression which is responsible for the high morbidity and mortality induced by secondary infections. Dendritic cells (DC) are professional antigen-presenting cells required for initiation of primary immune responses. To determine whether infection of DC by measles virus (MV) may play a role in virus-induced suppression of cell-mediated immunity, we examined the ability of CD1a+ DC derived from cord blood CD34+ progenitors and Langerhans cells isolated from human epidermis to support MV replication. Here we show that both cultured CD1a+ DC and epidermal Langerhans cells can be infected in vitro by both vaccine and wild type strains of MV. DC infection with MV resulted within 24-48 h in cell-cell fusion, cell surface expression of hemagglutinin, and virus budding associated with production of infectious virus. MV infection of DC completely abrogated the ability of the cells to stimulate the proliferation of naive allogeneic CD4+ T cell as early as day 2 of mixed leukocyte reaction (MLR) (i.e., on day 4 of DC infection). Mannose receptor-mediated endocytosis and viability studies indicated that the loss of DC stimulatory function could not be attributed to the death or apoptosis of DC. This total loss of DC stimulatory function required viral replication in the DC since ultraviolet (UV)-inactivated MV or UV-treated supernatant from MV-infected DC did not alter the allostimulatory capacity of DC. As few as 10 MV- infected DC could block the stimulatory function of 10(4) uninfected DC. More importantly, MV-infected DC, in which production of infectious virus was blocked by UV treatment or paraformaldehyde fixation, actively suppressed allogeneic MLR upon transfer to uninfected DC-T-cultures. Thus, the mechanisms which contribute to the loss of the allostimulatory function of DC include both virus release and active suppression mediated by MV-infected DC, independent of virus production. These data suggest that carriage of MV by DC may facilitate virus spreading to secondary lymphoid organs and that MV replication in DC may play a central role in the general immune suppression observed during measles.

Class I-restricted CTL induction by mucosal immunization with naked DNA encoding measles virus haemagglutinin

We have investigated the class I-restricted CTL response specific for measles virus haemagglutinin (HA) in the spleens of mice immunized by various mucosal routes with a DNA plasmid carrying the HA gene (pV1j-HA). A single immunization with recombinant DNA injected in the buccal mucosa induced an HA-specific CTL response. Similarly, nasal immunization with the DNA vaccine induced primary CTLs against measles virus HA. Booster immunization did not enhance the CTL activity. Oral or intrajejunal immunization with the plasmid induced a CTL response of lower magnitude. However, this could be potentiated by co-administration of the mucosal adjuvant cholera toxin or cationic lipids (DOTAP). These data show that a CTL response can be generated by mucosal vaccination using DNA vaccines.

Mucosal and systemic immune responses to measles virus haemagglutinin in mice immunized with a recombinant vaccinia virus

The immune response to a vaccinia virus recombinant expressing the measles virus haemagglutinin (VV-HA) was compared after parenteral or mucosal immunizations in mice. Parenteral immunizations with 10(6) p.f.u. VV-HA induced HA-specific antibody-producing cells (IgG>IgA) and HA-specific class I-restricted cytotoxic T lymphocytes (CTL) in the spleen. In contrast, intranasal administrations of 10(6) p.f.u. of VV-HA induced HA-specific spot-forming cells in the spleen (IgG>IgA) and the lungs (IgA>IgG), and HA-specific CTL in the spleen. Co-immunization by the nasal route with VV-HA and cholera toxin enhanced HA-specific immune responses. Oral immunizations with 10(8) p.f.u. of VV-HA generated low numbers of HA-specific IgA-producing cells in the lamina propria of the gut, and a weak HA-specific CTL activity in the spleen and mesenteric lymph nodes. Oral co-immunization with VV-HA and cholera toxin greatly enhanced the level of HA-specific spot-forming cells in the lamina propria (IgA>IgG). Interestingly, intrajejunal immunizations with 10(8) p.f.u. VV-HA alone induced high levels of anti-HA IgG-producing cells in the spleen and anti-HA IgA-secreting cells in the lamina propria of the gut. These data show that (i) VV-HA by the nasal route is immunogenic and generates a measles-specific mucosal immune response in the lung, which represents the primary site of replication of measles virus and that (ii) VV-HA can also induce measles-specific immunity in the intestine provided that it is protected from degradation in the gastrointestinal tract, or that cholera toxin is used as an adjuvant.

Intestinal epithelial cell line induction of T cell differentiation from bone marrow precursors

The mechanism whereby the intestinal microenvironment promotes T cell development in the absence of the thymus is unknown. We show that the murine intestine-derived epithelial cell line, MODE-K, can induce T cell differentiation marker expression in vitro on bone marrow (BM) T cell precursors. Three-color flow cytometry analysis of T-cell-depleted C3H BM mononuclear cells (MNC) after 4 days of coculture on monolayers of MODE-K indicated that approximately 25% of MNC expressed CD3 and TCR alpha beta. Of these CD3+ cells, 36% were CD3loCD4-CD8- double negative (DN), 34% were CD3loCD4+CD8 alpha beta+ double positive (DP), and the remainder were CD3hiCD4+CD8- or CD3hiCD4-CD8 alpha beta+ single positive (SP). In addition, the T cells which developed in coculture with MODE-K expressed the early T cell differentiation marker CD24 (heat-stable antigen). These T cells subsets did not develop when BM was cocultured with the LTA fibroblast cell line or in medium alone. Interestingly, preventing cell contact between MODE-K and BM by culturing in Transwell plates did not interfere with the development of T cells expressing the DN, DP, or SP phenotypes. Double-positive T cells did not develop if splenic MNC were cocultured with MODE-K. These results suggest that the intestinal epithelial environment can induce and support the T cell development from bone marrow precursors.

Lack of oral tolerance but oral priming for contact sensitivity to dinitrofluorobenzene in major histocompatibility complex class II-deficient mice and in CD4+ T cell-depleted mice

Oral tolerance is defined by immune unresponsiveness after oral administration of soluble antigens and by antigen-specific inhibition of peripheral immune responses induced by prior antigen feeding. The aim of this study was to investigate the implication of the major histocompatibility complex (MHC) class II presentation pathway to CD4+ T cells in oral tolerance of contact sensitivity (CS) to the hapten dinitrofluorobenzene (DNFB). We used MHC class II knockout (AB0/0) and invariant chain knockout (Ii0/0) mice, which have, respectively, a total or partial defect in class II-restricted activation of CD4+ T cells, as well as normal C57BL/6 mice depleted of CD4+ T cells by injection of a specific antibody. Intragastric administration of DNFB prior to skin sensitization induced specific inhibition of contact sensitivity to DNFB in A beta +/0 and Ii+/0 heterozygotes comparable to that observed in C57BL/6 mice. In contrast, no oral tolerance was observed in either MHC class II-deficient A beta 0/0 and Ii0/0 homozygote mutants or in syngeneic anti-CD4-depleted C57Bl/6 mice. Moreover, a single oral administration of DNFB, without skin sensitization, could prime A beta 0/0, Ii0/0 as well as anti-CD4-depleted C57BL/6 mice for DNFB-specific CS. These findings demonstrate that the class II/CD4 pathway is involved in oral tolerance manifested both as the inhibition of CS by hapten feeding prior to skin sensitization, and as immune unresponsiveness of normal mice to oral administration of hapten. Furthermore, our data provide evidence that a single oral feeding with DNFB is able to prime mice for hapten-specific CS, provided that the class II/ CD4 pathway is bypassed.

Antigen presentation in the murine oral epithelium

We have previously reported that the buccal mucosa can support delayed type hypersensitivity (DTH) reactions to contact sensitizers. In the present study, we show that cells isolated from the buccal epithelium are able to present soluble exogenous antigens to specific T cells. Single cell suspensions obtained by enzymatic dispersion of buccal epithelial sheets could present the native protein antigen hen-egg lysozyme (HEL) to the I-Ak-restricted CD4+ T-cell hybridoma specific for a.a 46-61 on HEL. T-cell activation resulted in interleukin-2 (IL-2) production which could be inhibited by anti-major histocompatibility complex (MHC) class-II antibodies of pertinent specificity. Immunohistochemical staining of whole buccal epithelial sheets revealed that all MHC II positive cells had a dendritic morphology and expressed ATPase activity, indicating that these cells represent a major antigen-presenting cell (APC) population in this tissue. Furthermore, single cell suspensions isolated from buccal epithelium (BEC) after local in vivo administration of either a native soluble protein, a synthetic dodecapeptide, or a contact sensitizer were able to activate antigen-specific T cells ex vivo. Kinetic analyses indicated that maximal APC activity in the oral epithelium occurred within 1 hr after local antigen administration, and had essentially vanished after 24 hr. Conversely, APC activity was undetectable in draining cervico-mandibular lymph node cell suspensions recovered 1 hr after local antigen injection but became manifest after 3-24 hr. These observations suggest that dendritic cells can acquire antigens in the buccal epithelium and migrate to draining lymph nodes where they present processed antigen to MHC class II-restricted T cells. This APC population may thus be a critical element in the initiation of Th1-driven DTH responses in the oral mucosa.

A role for stem cell factor and c-kit in the murine intestinal tract secretory response to cholera toxin

The role of stem cell factor (SCF) and its receptor (c-kit) in the intestinal secretory response to cholera toxin (CT) was investigated using a ligated intestinal loop model in mice having mutations in the dominant white spotting (W) locus and the steel (Sl) locus. W/Wv mice, which express an aberrant form of the c-kit protein, failed to give an intestinal secretory response after luminal CT challenge. In contrast, W/Wv mice and their control littermates had equivalent intestinal secretory responses to Escherichia coli heat-stable enterotoxin (STa). Sl/Sld mice, which express only a soluble truncated form of SCF, also gave a significantly reduced intestinal secretory response to CT when compared to the secretory response of their littermate controls. The unresponsiveness of W/Wv mice to CT was restricted to the intestinal tract since these mice had foot pad swelling responses to CT challenge that were equivalent to their littermate controls. Restoration of mast cells in W/Wv mice by bone marrow transplantation of control littermate bone marrow did not reverse the CT-unresponsiveness of the intestinal tract. Histological evaluation of the gastrointestinal tract from W/Wv mice showed a normal distribution of enterochromaffin cells (ECC). CT challenge of either ligated intestinal loops from C57B1/6 mice or a mouse intestinal epithelial cell line (MODE-K) resulted in elevated levels of mRNA for SCF. MODE-K cells exposed to CT also had enhanced expression of c-kit. Finally, fluid obtained from CT-challenged ligated intestinal loops from C57B1/6 mice contained significant levels of SCF. Taken together, the above results suggest that CT-induced intestinal secretory responses are dependent upon SCF-c-kit interactions. These interactions appear to be induced as a consequence of CT stimulation of the intestinal tract and may also play a role in the development or functionality of the enteric nervous system.

Major histocompatibility complex class I-restricted CD8+ T cells and class II-restricted CD4+ T cells, respectively, mediate and regulate contact sensitivity to dinitrofluorobenzene

Contact sensitivity (CS) is a form of delayed-type hypersensitivity to haptens applied epicutaneously and is thought to be mediated, like classical delayed-type hypersensitivity responses, by CD4+ T helper-1 cells. The aim of this study was to identify the effector T cells involved in CS. We studied CS to the strongly sensitizing hapten dinitrofluorobenzene (DNFB) in mice rendered deficient by homologous recombination in either major histocompatibility complex (MHC) class I, MHC class II, or both, and which exhibited deficiencies in, respectively, CD8+, CD4+, or both, T cells. MHC class I single-deficient and MHC class I/class II double-deficient mice, both of which have a drastic reduction in the number of CD8+ T cells, were unable to mount a CS response to DNFB. In contrast, both MHC class II-deficient mice and normal mice treated with an anti-CD4 monoclonal antibody (mAb) developed exaggerated and persistent responses relative to heterozygous control littermates. Furthermore, anti-CD8 mAb depletion of class II-deficient mice totally abolished their ability to mount an inflammatory response to DNFB. Removal of residual CD4+ T cells in class II-deficient mice by anti-CD4 mAb treatment did not diminish the intensity of CS. These data clearly demonstrate that class I-restricted CD8+ T cells are sufficient for the induction of CS to DNFB, and further support the idea that MHC class II-restricted CD4+ T cells down-regulate this inflammatory response.

Interleukin-12 increases interleukin-4 production by established human Th0 and Th2-like T cell clones

Interleukin (IL)-12 is a potent inducer of cell-mediated immunity: it favors the generation of interferon (IFN)-gamma-producing T cells, increases IFN-gamma production by T cells and natural killer cells and prevents the generation of a Th2 response in murine in vivo models. Nevertheless, the effects of IL-12 on an established Th2 response remain poorly documented. In the present paper, we analyzed the effect of IL-12 on the profile of lymphokines produced by established IL-4-producing Th0 and Th2-like human T cell clones (TCC) and by polyclonal T cells. We found that IL-12 (i) enhances, as previously reported, IFN-gamma production by Th0 TCC and, to a smaller extent, by Th2-like TCC, (ii) increases the proliferation of Th0 and Th2-like TCC and (iii) unexpectedly, synergizes with T cell receptor-associated or nonspecific stimuli in increasing IL-4 production by these TCC. Thus, IL-12 potentiates the production of IFN-gamma and also of IL-4 by established IL-4 producing TCC. Although IL-12 has been widely reported to induce a Th1 response and to prevent the development of a Th2 response in vivo, IL-12 may on the contrary potentiate an established Th2 response in humans.

Oral tolerance to haptens: intestinal epithelial cells from 2,4-dinitrochlorobenzene-fed mice inhibit hapten-specific T cell activation in vitro

The mechanisms underlying the induction of immunological tolerance after feeding soluble exogenous antigens, including proteins and haptens, are still unclear. Using a model of oral tolerance to the contact-sensitizing hapten 2,4-dinitrochlorobenzene (DNCB), we have compared the ability-of intestinal epithelial cells and of Peyer's patch APC to present DNCB in vitro or ex vivo after oral feeding, to specific peripheral lymph node T cells from DNCB-sensitized mice. In contrast to Peyer's patch APC, which induce efficient hapten-specific T cell activation upon exposure to the hapten either in vitro or in vivo, mature MHC class-II-positive intestinal epithelial cells were unable to induce T cell activation in either case. Interestingly, enterocytes from DNCB-fed mice exerted a dramatic inhibitory effect on the proliferative response of hapten-primed T cells in response to dinitrobenzene sulfonate presented by syngeneic spleen cells. This inhibitory effect, which was also observed with supernatant of intestinal epithelial cells from DNCB-fed mice, could be reversed by neutralizing anti-transforming growth factor (TGF)-beta antibodies. In addition, pre-incubation of hapten-sensitized T cells with enterocytes from DNCB-fed mice induced T cell anergy, which could be reversed by exogenous interleukin-2 or interleukin-4. These data demonstrate that intestinal epithelial cells activated in vivo by oral administration of DNCB are able to block proliferation of activated T cells through secretion of immunosuppressive cytokines such as TGF-beta. It is proposed that intestinal epithelial cells may play a significant role in oral tolerance by limiting T cell-mediated hypersensitivity responses.

CD23/CD21 interaction is required for presentation of soluble protein antigen by lymphoblastoid B cell lines to specific CD4+ T cell clones

Previous studies have documented a role for membrane-bound CD23 (the low affinity Fc epsilon RII) in presentation of alloantigens by B cells. The aim of the present study was to examine the involvement of cell surface CD23 in presentation of more conventional soluble protein antigens to T cells. We show that antibodies to CD23 and to its lymphocyte-associated second ligand, CD21, inhibit presentation of the cow's milk allergen casein, by autologous CD23+CD21+ B-EBV cell lines to casein-specific HLA-DP-restricted CD4+ T cell clones obtained from patients with either reaginic or enterophatic forms of cow's milk protein intolerance. Maximal inhibition was achieved when the antibodies were added at the initiation of the culture. The absence of specific inhibition by an anti-DR alpha monoclonal antibody (mAb) argues against a steric hindrance phenomenon impeding access of the T cell receptor to major histocompatibility complex class II molecules. Rather, anti-CD23 and anti-CD21 mAb-induced inhibition of antigen presentation seems to affect at least partly, heterotypic conjugate formation through CD23/CD21 interaction. Double immunofluorescence labeling of the T cell clones and antibody inhibition of T/B conjugate formation shows that functional CD23 and CD21 molecules are induced on T cells following contact with B-EBV cell lines. Taken together, these data indicate that CD23/CD21 interactions between T and B cells are required for presentation of soluble protein antigens by B-EBV cell lines to specific CD4+ T cells. The potential implications of these findings for allergen-specific T cell activation are discussed.

Familial autoimmune enteropathy with circulating anti-bullous pemphigoid antibodies and chronic autoimmune hepatitis

In a family of four children (two boys and two girls), the two brothers had severe, protracted watery diarrhea beginning at 2 and 3 weeks of life, respectively. Duodenal mucosa in both patients showed total villous atrophy and severe inflammatory infiltration of the entire bowel. The first patient also had lymphoid cell infiltration of the pancreas and died at 6 weeks of age. The second boy is alive at 2 years of age and is immunocompetent, but still receives total parenteral nutrition. Indirect immunofluorescence studies revealed circulating antibodies to enterocytes, smooth muscle, thyroid, and islet cells. Bullous pemphigoid antibodies (230 and 180 kd), specific for hemidesmosomal proteins and usually associated with a subepidermal blistering skin disease, were detected by direct and indirect immunofluorescence studies and by Western immunoblot. A diagnosis of autoimmune hepatitis was made, based on evidence of chronic active hepatitis and circulating anti-smooth muscle antibody. Immunosuppressive treatments induced partial clinical remission of the diarrhea but no resolution of the small bowel injury. At 16 months of age, remission of the diarrhea occurred, but persistent autoimmune hepatitis led us to maintain treatment with prednisone and azathioprine, and later with cyclosporine. In this child, as in other patients with autoimmune disease, the link between autoantibodies and organ damage remains uncertain but immunosuppressive treatment is indicated.

Rat cluster of differentiation 1 molecule: expression on the surface of intestinal epithelial cells and hepatocytes

BACKGROUND/AIMS

Cluster of differentiation 1 (CD1) is a family of nonpolymorphic, major histocompatibility complex class I-like molecules with prominent expression in the liver and intestinal epithelium of humans and mice. Models of intestinal and hepatobiliary inflammation and experimental liver transplantation are conducted in the rat, yet nothing is known of CD1 expression in this species.

METHODS

Monoclonal antibodies against murine CD1 were used to identify a rat CD1 homologue. Tissue messenger RNA expression was confirmed by Northern blot analysis with a murine CD1 complementary DNA probe.

RESULTS

Immunoperoxidase staining detected CD1 in intestinal epithelial and liver cells but not in the thymus. Immunofluorescence of isolated hepatocytes and a rat fetal intestinal cell line, SLC-44, showed cell surface expression of CD1. Metabolic labeling and immunoprecipitation of the SLC-44 cell line and a mouse intestinal epithelial cell line, MODE-K, showed a protein of 55 kilodaltons. Immunoblotting of CD1 in isolated intestinal epithelial cells and hepatocytes showed a molecule of 55 kilodaltons. Northern blot analysis showed a single message of approximately 2.2 kilobases in hepatocytes.

CONCLUSIONS

A CD1 homologue exists in the rat. Expression in the rat intestine and liver are similar to those in the human and mouse. The rat may be useful as a model for the study of CD1 function.

Immortalization of mouse intestinal epithelial cells by the SV40-large T gene. Phenotypic and immune characterization of the MODE-K cell line

Intestinal epithelial cells from the mouse small intestine were immortalized by SV40 large T gene transfer through a murine ecotropic virus. The resulting cell lines expressed the SV40 large T mRNA and exhibited morphological and phenotypic characteristics of normal enterocytes, including intercellular junctions, and expression of cytokeratin, villin, poly-Ig receptor (i.e., secretory component) and vasoactive intestinal peptide receptors. All expressed cell surface major histocompatibility complex class I molecules, but cell surface class II antigens were undetectable. Functional studies on antigen presentation were carried out using the MODE-K cell line established from the mouse duodenum. Interferon-gamma treatment of MODE-K cells resulted in a high level of class II molecule expression, and the ability to process and present native protein antigens to specific CD4+ T-cell hybridomas, via functional class II molecules. These data suggest that the MODE-K cell line is a suitable model for the analysis of intestinal epithelial cell function in mucosal immunity.

Unexpected lack of reactivity of allogeneic anti-Ia monoclonal antibodies with MHC class II molecules expressed by mouse intestinal epithelial cells

We have examined MHC class II molecules expression by murine gut epithelial cells using a large panel of anti-Ia antibodies. In contrast to conventional APC (i.e., B cells and macrophages), only two anti-Ia antibodies reacted with enterocytes: a xenogeneic rat anti-Ia mAb (CD311) directed against a monomorphic class II determinant, and a polyclonal antiserum directed against both I-A and I-E heterodimers. In contrast, allogeneic anti-Ia mAb were either unreactive (17 of 20) or reacted weakly (3 of 20) with enterocytes, even after in vivo treatment with IFN-gamma. This pattern of Ia reactivity of epithelial cells was tissue specific (restricted to gut mucosa) and cell specific (restricted to gut epithelial cells). Biochemical and molecular studies confirmed that enterocytes expressed I-A and I-E isotypes on their cell surface and contained mRNA of both subregion loci. Interestingly, enterocytes appeared deficient in expression of the MHC class II-associated invariant chain, and are not able to stimulate allogeneic T cells. These data suggest that gut epithelial cells express a conformation of class II molecules, antigenically distinct from that expressed on conventional APC.

Unexpected lack of reactivity of allogeneic anti-Ia monoclonal antibodies with MHC class II molecules expressed by mouse intestinal epithelial cells

We have examined MHC class II molecules expression by murine gut epithelial cells using a large panel of anti-Ia antibodies. In contrast to conventional APC (i.e., B cells and macrophages), only two anti-Ia antibodies reacted with enterocytes: a xenogeneic rat anti-Ia mAb (CD311) directed against a monomorphic class II determinant, and a polyclonal antiserum directed against both I-A and I-E heterodimers. In contrast, allogeneic anti-Ia mAb were either unreactive (17 of 20) or reacted weakly (3 of 20) with enterocytes, even after in vivo treatment with IFN-gamma. This pattern of Ia reactivity of epithelial cells was tissue specific (restricted to gut mucosa) and cell specific (restricted to gut epithelial cells). Biochemical and molecular studies confirmed that enterocytes expressed I-A and I-E isotypes on their cell surface and contained mRNA of both subregion loci. Interestingly, enterocytes appeared deficient in expression of the MHC class II-associated invariant chain, and are not able to stimulate allogeneic T cells. These data suggest that gut epithelial cells express a conformation of class II molecules, antigenically distinct from that expressed on conventional APC.

Mouse intestinal epithelial cells express the self superantigen Mls1a

In previous studies, we demonstrated that intestinal epithelial cells of the mouse small intestine could present exogenous antigen to specific CD4+ T cell hybridomas. We now report on the ability of normal enterocytes to present the self superantigen Mls1a. Enterocytes from Mls1a but not from Mls1b strains stimulated interleukin-2 production through a V beta 6+ T cell hybridoma specific for Mls1a determinants. Antibody inhibition experiments showed that enterocytes presented Mls determinants via a major histocompatibility complex class II-dependent mechanism. Furthermore, the ability of enterocytes to activate V beta 6+ Mls1a-specific T cells was inhibited by monoclonal antibodies against the Orf protein encoded by an Mtv-7 provirus which is associated with Mls1a expression. These findings provide evidence for the first time that Mls determinants are expressed on normal enterocytes and support the theory of a possible role of these cells in extrathymic selection of T cell receptor V beta repertoire of intraepithelial T lymphocytes.

Intestinal epithelial cells express the CD23/Fc epsilon RII molecule: enhanced expression in enteropathies

Immunohistochemical analysis of normal human intestine revealed that two anti-CD23 monoclonal antibodies (mAb), EBVCS 1 and EBVCS 2, reacted with human intestinal epithelial cells. Both mAb exhibited an exclusive reactivity with epithelial cells of the small and large bowels. Staining with both EBVCS 1 and EBVCS 2 was localized on the apical and basal sides of enterocytes. Enhanced expression of CD23 on gut epithelial cells was found in inflammatory bowel diseases, in children with food intolerance to cows' milk proteins and in a young infant with severe autoimmune enteropathy. Western blot analysis of anti-CD23 mAb reactivity with gut epithelial cell extracts showed the presence of a non-reducible 42,000-45,000 M(r) polypeptide compatible with the membrane form of the intact CD23 molecule. These data show that CD23 is constitutively expressed by intestinal epithelial cells and that its expression is enhanced in enteropathies.

[CD23: structures, functions and practical perspectives in allergy reactions]

CD23, the low-affinity receptor for IgE, is a surface cell marker and surface CD23 is cleaved into soluble fragments by an autocatalytic mechanism. cDNA clone encoding for CD23 has been isolated and structural studies realized. CD23 is expressed by B and T lymphocytes and by other cells including tumor cells. IL4 and IgE are the most potent inducer of CD23 expression. CD23 has multiple functions: B cell growth and differentiation, capacity to present antigen, cellular mobility, inflammation... The serum sCD23 level is often increased in allergic patients.