Fetal calf serum-primed dendritic cells induce a strong anti-fetal calf serum immune response and diabetes protection in the non-obese diabetic mouse

In recent years, several investigators have shown that transfer of dendritic cells (DC) prevents diabetes development in non-obese diabetic (NOD) mice. Accumulating evidences showing that DC cultured in medium containing fetal calf serum (FCS) can induce a dominant unspecific immune response in tumor models after i.v. injection prompted us to investigate if the protecting effect of DC on diabetes development in NOD mice might be supported by the induction of an anti-FCS immune response in recipient mice. Five-week-old NOD mice were injected i.v. with FCS-cultured bone marrow-derived DC or PBS as control. Levels of anti-FCS and anti-bovine serum albumin (BSA) antibodies were measured in the serum of recipient mice. Anti-FCS cellular immune responses were also analysed after a single DC injection using in vitro proliferation of splenocytes either in RPMI supplemented with FCS, AIMV-BSA or RPMI containing autologous mouse serum or BSA as a read out. DC injection prevented diabetes development in NOD mice and high titers of anti-FCS and anti-BSA antibodies were detected in serum of all DC-injected mice. Besides, splenocytes isolated from DC-injected mice proliferated vigorously in the presence of bovine proteins in contrast to splenocytes isolated from control mice but removing bovine proteins abrogated the high level of proliferation of those splenocytes suggesting that lymphocytes have been primed against bovine proteins in vivo after DC injection. All together, our data show that DC transfer induced cellular and humoral anti-FCS immune responses in recipient NOD mice suggesting that the protective effect of DC relies on their unspecific immunostimulatory effects.

Feeding NOD mice with pig splenocytes induces transferable mechanisms that modulate cellular and humoral xenogeneic reactions against pig spleen or islet cells

We have reported previously that oral administration of pig cells to NOD mice modified xenogeneic cellular response against pig islet cells (PICs), and hypothesized that it may have induced active suppression. This preliminary report evaluated only the effect of feeding pig cells by 'primary' proliferation, i.e. when splenocytes from fed mice are confronted with pig cells in vitro. The present study also considered 'secondary' proliferation and cytokine production after feeding and subsequent in vivo graft of pig cells. Additionally, serum IgM and IgG isotypes were quantified by ELISA using pig target cells. Induction of active mechanism by feeding was hypothetical, which led us here to transfer splenocytes from mice fed pig spleen cells (PSC) and evaluate 'primary' (after transfer) and 'secondary' (after transfer and subsequent graft of pig cells) proliferations and cytokine secretions in recipient mice. We also determined whether the effects of feeding pig cells persisted after depression of suppressor mechanisms by cyclophosphamide. Mice fed with PSC displayed increased 'primary' splenocyte proliferation to PSC or PIC (P < 0.0001), while 'secondary' responses were decreased (P < 0.03) in those fed PSC and subsequently grafted with PSC. The increased 'primary' and decreased 'secondary' proliferations were reduced (P < 0.04) by pretreatment with cyclophosphamide. The IL-10/ and IL-4/IFNgamma ratios produced in response to PSC increased (P < 0.04) in mice fed and grafted with PSC compared to those grafted only with PSC. IgM and IgG levels against pig cells were, respectively, increased (P < 0.04) and decreased (P < 0.04) in mice fed and grafted with PSC. IgG2a and IgG2b, but not IgG1, levels were lower (P < 0.01). These effects of feeding PSC on 'secondary' proliferation, cytokine and antibody productions, were not detected when mice were fed PSC only after graft with PSC. Transfer with splenocytes from mice fed PSC increased 'primary' proliferation of splenocytes from recipient mice in response to PSC (P < 0.02) or PIC (P < 0.05). After transfer with splenocytes from PSC-fed mice and graft with PSC, 'secondary' proliferation to pig cells were reduced (P < 0.04), and the IL-10/IFNgamma ratio produced in response to PSC was increased fourfold. Thus, oral administration of PSC induces active transferable mechanisms, characterized by a biphasic pattern with early increased 'primary' xenogeneic cellular reactions to both PSC and PIC, followed by decreased 'secondary' responsiveness and a concomitant shift of the Th1/Th2 balance towards greater Th2 influence. Decreased responsiveness may be due to active suppression, even though induction of anergy or deletion cannot be excluded.

Expression of ActA, Ami, InlB, and listeriolysin O in Listeria monocytogenes of human and food origin

Expression of proteins involved in the adhesion of Listeria monocytogenes to mammalian cells or in the intracellular life cycle of this bacterium, including listeriolysin O (LLO), ActA, Ami, and InlB, was used to compare two populations of L. monocytogenes strains. One of the populations comprised 300 clinical strains, and the other comprised 150 food strains. All strains expressed LLO, InlB, and ActA. No polymorphism was observed for LLO and InlB. Ami was detected in 283 of 300 human strains and in 149 of 150 food strains. The strains in which Ami was not detected were serovar 4b strains. Based on the molecular weights of the proteins detected, the strains were divided into two groups with Ami (groups Ami1 [75% of the strains] and Ami2 [21%]) and into four groups with ActA (groups ActA1 [52% of the strains], ActA2 [18%], ActA3 [30%], and ActA4 [one strain isolated from food]). Logistic regression showed that food strains were more likely to belong to group ActA3 than human strains (odds ratio [OR] = 2.90; P = 1 x 10(-4)). Of the strains isolated from patients with non-pregnancy-related cases of listeriosis, bacteremia was predominantly associated with group Ami1 strains (OR = 1.89; P = 1 x 10(-2)) and central nervous system infections were associated with group ActA2 strains (OR = 3.04; P = 1 x 10(-3)) and group ActA3 strains (OR = 3.91; P = 1 x 10(-3)).

In vitro recognition and impairment of pig islet cells by baboon immune cells: similarity to human cellular reactions

BACKGROUND

Grafting pig islets into patients with type 1 diabetes requires control of the strong cellular xenogeneic rejection. This in vitro study compared the cellular reaction of baboons and humans to pig islet cells (PICs) to confirm the validity of using these animals for further in vivo preclinical trials.

METHODS

Baboon or human peripheral blood mononuclear cells (PBMCs) or subsets were co-incubated with PICs from specific pathogen-free adult pigs for 7 days to determine the mechanisms and intensity of PBMC proliferation. Interleukin (IL) 10 and interferon (IFN) gamma secretion were assessed by enzyme-linked immunosorbent assay. Because proliferation was not indicative of aggression, a test based on perifusion analysis of the alteration of basal and stimulated insulin releases from PIC incubated with different baboon and human cells was developed.

RESULTS

Baboon PBMCs strongly proliferated in response to PICs (stimulation index [SI]=24.8+/-6.9 [n=8] vs. 23.9+/-3.4 [n=34] for human PBMCs), showing considerable variation in intensity among animals (2.3<SI<63) and humans (1.8<SI<97). PBMC proliferation was inhibited in baboons and humans by anti-CD4 (% inhibition of SI: 71+/-10% and 75+/-7%, respectively) and anti-DR (75+/-35% and 80+/-6%) monoclonal antibodies (MoAbs) or by depletion of MHC class II+ cells (99+/-1% and 90+/-6%). Blocking by anti-CD8 or anti-CD16 MoAbs was weaker and variable among both animals and humans. IL-10 production by baboon and human PBMCs in response to PICs increased more than IFN-gamma production after 2 days of coculture, but the IL-10/IFN-gamma ratio was inverted after 5 days of coculture. After 7 days (and even after only 2 days) of coculture with baboon (n=8) or human (n=18) PBMCs, basal and glucose-stimulated insulin secretions from PICs were almost completely abolished (P<0.0001). The drop in insulin release could have mainly resulted from lysis of PICs, because the number of PICs decreased by 78% after 7 days of co-incubation with PBMCs. A decrease of insulin release by PBMCs was reproduced with plastic-adherent cells and was abolished by depletion of MHC class II+ cells or by addition of 100 microg/ml gadolinium (which inhibits macrophages), but not by cyclosporine. In baboons, as in humans, insulin release was also decreased after coculture of PICs with enriched T lymphocytes remixed with antigen-presenting cells (APCs).

CONCLUSIONS

This study provides the first data on in vitro comparison of baboon and human cell-mediated recognition and impairment of PICs. Proliferation of PBMCs against PICs involves mainly CD4 T cells, with indirect recognition mediated by baboon or human MHC class II+ APCs. The Th2/Th1 profile of cytokines secreted in response to PICs was similar in baboon and human PBMCs. The model based on alteration of insulin secretion indicates that PIC impairment by whole mononuclear cells was strong and rapid and that a crucial role was played by MHC class II+ and plastic-adherent cells. Two mechanisms appear to be responsible for the role of these cells: (1) early and strong direct effect, which is potentially involved in vivo in primary nonfunction of islets aggressed by monocytes and macrophages; and (2) presentation of PIC xenoantigens, which leads to impairment by T lymphocytes possibly involved in in vivo-specific cellular rejection. The mechanisms and intensity of baboon cellular reactions to PICs in vitro were similar to those observed in humans, which suggests that the baboon is a suitable model for the study of cellular mechanisms during preclinical trials of pig islet xenografts.

A role for cofilin and LIM kinase in Listeria-induced phagocytosis

The pathogenic bacterium Listeria monocytogenes is able to invade nonphagocytic cells, an essential feature for its pathogenicity. This induced phagocytosis process requires tightly regulated steps of actin polymerization and depolymerization. Here, we investigated how interactions of the invasion protein InlB with mammalian cells control the cytoskeleton during Listeria internalization. By fluorescence microscopy and transfection experiments, we show that the actin-nucleating Arp2/3 complex, the GTPase Rac, LIM kinase (LIMK), and cofilin are key proteins in InlB-induced phagocytosis. Overexpression of LIMK1, which has been shown to phosphorylate and inactivate cofilin, induces accumulation of F-actin beneath entering particles and inhibits internalization. Conversely, inhibition of LIMK's activity by expressing a dominant negative construct, LIMK1(-), or expression of the constitutively active S3A cofilin mutant induces loss of actin filaments at the phagocytic cup and also inhibits phagocytosis. Interestingly, those constructs similarly affect other actin-based phenomenons, such as InlB-induced membrane ruffling or Listeria comet tail formations. Thus, our data provide evidence for a control of phagocytosis by both activation and deactivation of cofilin. We propose a model in which cofilin is involved in the formation and disruption of the phagocytic cup as a result of its local progressive enrichment.

Listeria protein ActA mimics WASp family proteins: it activates filament barbed end branching by Arp2/3 complex

Actin-based propulsion of the bacteria Listeria and Shigella mimics the forward movement of the leading edge of motile cells. While Shigella harnesses the eukaryotic protein N-WASp to stimulate actin polymerization and filament branching through Arp2/3 complex, the Listeria surface protein ActA directly activates Arp2/3 complex by an unknown mechanism. Here we show that the N-terminal domain of ActA binds one actin monomer, in a profilin-like fashion, and Arp2/3 complex and mimics the C-terminal domain of WASp family proteins in catalyzing filament barbed end branching by Arp2/3 complex. No evidence is found for side branching of filaments by ActA-activated Arp2/3 complex. Mutations in the conserved acidic (41)DEWEEE(46) and basic (146)KKRRK(150) regions of ActA affect Arp2/3 binding but not G-actin binding. The motility properties of wild-type and mutated Listeria strains in living cells and in the medium reconstituted from pure proteins confirm the conclusions of biochemical experiments. Filament branching is followed by rapid debranching. Debranching is 3-4-fold faster when Arp2/3 is activated by ActA than by the C-terminal domain of N-WASp. VASP is required for efficient propulsion of ActA-coated beads in the reconstituted motility medium, but it does not affect the rates of barbed end branching/debranching by ActA-activated Arp2/3 nor the capping of filaments. VASP therefore affects another still unidentified biochemical reaction that plays an important role in actin-based movement.

Co-incubation of pig islet cells with spleen cells from non-obese diabetic mice causes decreased insulin release by non-T-cell- and T-cell-mediated mechanisms

In vitro studies were conducted in the non-obese diabetic (NOD) mouse, prone to Type 1 autoimmune diabetes, to investigate the mechanisms involved in cell-mediated rejection of pig islet xenografts. Our previous work concerning the mechanisms of proliferation of xenogeneic lymphocytes to pig islet cells (PIC) was not indicative of PIC impairment. Consequently, a test was developed based on perifusion analysis of the alteration of basal and stimulated insulin release from adult PIC incubated with mouse splenocytes or subsets. Compared with PIC incubation alone or with syngeneic pig splenocytes, co-incubation with mouse whole spleen cells resulted in a decrease of basal and stimulated insulin release (P < 0.001). Two components of this alteration were detected separately: PIC impairment was decreased (P < 0.01) after removal of plastic-adherent cells from spleen cells, but maintained (P < 0.01) when plastic-adherent cells alone were co-incubated with PIC. The increase of murine interleukin-1 beta when mouse plastic-adherent spleen cells were cultured with PIC (P < 0.04) was indicative of macrophage activation. Soluble factors produced during co-incubation of mouse splenocytes or plastic-adherent cells with PIC were involved in the impairment process, since supernatant fluids collected during previous PIC-mouse cell co-incubations directly altered (P < 0.01) insulin release from PIC. Moreover, impairment of PIC by mouse spleen cells was abolished (P < 0.01) by gadolinium chloride (which inhibits macrophages), but not by cyclosporin A. Another mechanism was apparent, since co-incubation of PIC with purified mouse T cells or CD4+ T cells, re-mixed with antigen-presenting cells, led to a decrease (P < 0.01) of insulin release. This model, based on the alteration of dynamic basal and stimulated insulin release, is indicative of in vitro cell-mediated alteration of PIC in the NOD mouse. The effect of whole spleen cells was rapid, and a crucial role was played by plastic-adherent cells. Two mechanisms were responsible for the behaviour of these cells: an early direct effect (at least in part via soluble products); and the indirect presentation of PIC xenoantigens (leading to impairment by CD4+ T lymphocytes).

In vitro co-incubation of pig islet cells with xenogeneic human blood mononuclear cells causes loss of insulin release during perifusion: involvement of non-T-cell- and T-cell-mediated mechanisms

Because the different steps of the human cellular immune rejection of pig islets are still poorly understood, our previous work concerned the intensity and mechanisms of the proliferation of human peripheral blood mononuclear cells (PBMC) to adult pig islet cells (PIC). As lymphocyte proliferation is not indicative of alteration of PIC, the present in vitro study evaluated cell-mediated immune effectors possibly involved in impairment of adult PIC. A test was thus developed, based on perifusion analysis of the alteration of insulin release from PIC incubated with different human cells. Compared to PIC incubation alone or with autologous pig splenocytes, seven-day co-incubation with whole human peripheral blood mononuclear cells (PBMC) (n = 18) led to almost complete abolition of basal and stimulated insulin releases (p < 0.0001). This effect could not be reversed by extensive sequential washes before perifusion of PIC, and the number of PIC was decreased by 78% after seven-day co-incubation with PBMC. PBMC are a complex mixture of cells involved in different xenogeneic mechanisms, and two components of this PIC impairment were then detected separately. First, the effect of PBMC against PIC was decreased (p < 0.0001) after removal of either MHC class II+ or CD14+ cells from PBMC. On the contrary, decreasing effect (p < 0.001) on insulin secretion was observed when only plastic-adherent or CD14+ cells were co-incubated with PIC. Additionally, alteration of insulin release from PIC cultured with PBMC or plastic-adherent cells was abolished dose-dependently (p < 0.0001 and p < 0.04, respectively) by gadolinium chloride (which inhibits macrophages), but not modified by cyclosporin A or mycophenolate mofetil which did not alter insulin release from PIC but blocked the proliferation of PBMC against PIC. A second mechanism was also detected, since co-incubation of PIC with purified human T cells remixed with antigen-presenting cells led to a decrease (p < 0.0001) of insulin release. This model based on the alteration of dynamic basal and stimulated insulin secretion provides detailed account of in vitro human cell-mediated impairment of PIC. It shows that the xenogeneic effect of whole mononuclear cells was strong and rapid. A crucial role was played by MHC class II+, CD14+, and plastic-adherent cells. Two mechanisms appear to be responsible for the role of these cells: 1) early direct effect, potentially involved in vivo in primary nonfunction of islets aggressed by monocytes/macrophages; and 2) the presentation of PIC xenoantigens leading to impairment by T lymphocytes, which may be involved in in vivo specific cellular rejection.

[Acceptability of xenograft in type 1 diabetic patients and by the general French population]

OBJECTIVE

The possibility of using pig xenografts raises the questions of their acceptability and the reasons for reluctance by patients and society, which have not been clearly investigated in Europe.

RESEARCH DESIGN AND METHODS

A survey using a multiple-choice questionnaire was conducted to quantify the acceptability of pig xenografts in type 1 diabetic patients potentially concerned by xenografts (n = 377) as compared to a sample of the French population (n = 697).

RESULTS

Willingness to accept a xenograft was significantly greater among diabetic patients than the general population (64% vs 54%, P < 0.001). The notion of using pig xenografts appears to be rather well accepted by the general population, and more information might improve acceptability. The acceptance of xenografts in general and pig tissues in particular was higher in diabetic patients.

CONCLUSIONS

Because the general population and type 1 diabetic patients are not aware of the sanitary risks specifically related to a xenograft, the decision to use xenografts cannot be based simply on the expectations of possible recipients. The sanitary risks need to be assessed before further xenografts are performed, particularly in diabetic patients whose risk/benefit ratio is not particularly favourable.

Listeria monocytogenes ActA protein interacts with phosphatidylinositol 4,5-bisphosphate in vitro

The N-terminal region of the Listeria monocytogenes ActA protein, in conjunction with host cell factors, is sufficient for actin polymerization at the bacterial surface. Previous data suggested that ActA could protect barbed ends from capping proteins. We tested this hypothesis by actin polymerization experiments in the presence of the ActA N-terminal fragment and capping protein. ActA does not protect barbed ends from capping protein. In contrast, this polypeptide prevents PIP(2) from inhibiting the capping activity of capping protein. Gel filtration and tryptophan fluorescence experiments showed that the purified ActA N-terminal fragment binds to PIP(2) and PIP, defining phosphoinositides as novels ligands for this functional domain of ActA. Phosphoinositide binding to the N-terminal region of ActA may induce conformational changes in ActA and/or facilitate binding of other cell components, important for ActA-induced actin polymerization.

A comparative study of the actin-based motilities of the pathogenic bacteria Listeria monocytogenes, Shigella flexneri and Rickettsia conorii

Listeria monocytogenes, Shigella flexneri, and Rickettsia conorii are three bacterial pathogens that are able to polymerize actin into ‘comet tail’ structures and move within the cytosol of infected cells. The actin-based motilities of L. monocytogenes and S. flexneri are known to require the bacterial proteins ActA and IcsA, respectively, and several mammalian cytoskeleton proteins including the Arp2/3 complex and VASP (vasodilator-stimulated phosphoprotein) for L. monocytogenes and vinculin and N-WASP (the neural Wiskott-Aldrich syndrome protein) for S. flexneri. In contrast, little is known about the motility of R. conorii. In the present study, we have analysed the actin-based motility of this bacterium in comparison to that of L. monocytogenes and S. flexneri. Rickettsia moved at least three times more slowly than Listeria and Shigella in both infected cells and Xenopus laevis egg extracts. Decoration of actin with the S1 subfragment of myosin in infected cells showed that the comet tails of Rickettsia have a structure strikingly different from those of L. monocytogenes or S. flexneri. In Listeria and Shigella tails, actin filaments form a branching network while Rickettsia tails display longer and not cross-linked actin filaments. Immunofluorescence studies revealed that the two host proteins, VASP and (α)-actinin colocalized with actin in the tails of Rickettsia but neither the Arp2/3 complex which we detected in the Shigella actin tails, nor N-WASP, were detected in Rickettsia actin tails. Taken together, these results suggest that R. conorii may use a different mechanism of actin polymerization.

Characterisation of a new operon encoding a Zur-like protein and an associated ABC zinc permease in Listeria monocytogenes

Metal ions uptake is mainly studied for iron, as it has often been implicated in bacterial virulence. Although Listeria monocytogenes virulence is expected to be controlled by the iron availability, little is known about such an uptake and its regulation. We describe the analysis of the first operon involved in metal ions uptake in L. monocytogenes. Its three ORFs encode respectively (1) an ABC protein, likely implicated in zinc uptake, (2) a hydrophobic membrane protein, generally associated with ABC proteins and (3) a ferric uptake regulator-like protein, that we named zinc uptake regulator, as it shows strong homologies with the zinc uptake regulator, a regulator of the zinc homeostasis in Bacillus subtilis. The expression of this operon is regulated by the zinc concentration.

Inducible recruitment of Cdc42 or WASP to a cell-surface receptor triggers actin polymerization and filopodium formation

BACKGROUND

Cdc42, a GTP-binding protein of the Rho family, controls actin cytoskeletal organization and helps to generate actin-based protruding structures, such as filopodia. In vitro, Cdc42 regulates actin polymerization by facilitating the creation of free barbed ends - the more rapidly growing ends of actin filaments - and subsequent elongation at these ends. The Wiskott- Aldrich syndrome protein, WASP, which has a pleckstrin-homology domain and a Cdc42/Rac-binding motif, has been implicated in cell signaling and cytoskeleton reorganization. We have investigated the consequences of local recruitment of activated Cdc42 or WASP to the plasma membrane.

RESULTS

We used an activated Cdc42 protein that could be recruited to an engineered membrane receptor by adding rapamycin as a bridge, and added antibody-coupled beads to aggregate these receptors. Inducible recruitment of Cdc42 to clusters of receptors stimulated actin polymerization, resulting in the formation of membrane protrusions. Cdc42-induced protrusions were enriched in the vasodilator-stimulated phosphoprotein VASP and the focal-adhesion-associated proteins zyxin and ezrin. The Cdc42 effector WASP could also induce the formation of protrusions, albeit of different morphology.

CONCLUSIONS

This is the first demonstration that the local recruitment of activated Cdc42 or its downstream effector, WASP, to a membrane receptor in whole cells is sufficient to trigger actin polymerization that results in the formation of membrane protrusions. Our data suggest that Cdc42-induced actin-based protrusions result from the local and serial recruitment of cytoskeletal proteins including zyxin, VASP, and ezrin.

Intensity and mechanisms of in vitro xenorecognition of adult pig pancreatic islet cells by CD4+ and CD8+ lymphocytes from type I diabetic or healthy subjects

The intensity and mechanisms of cell-mediated rejection of pig islet cells were studied in 49 Type I diabetic and 34 healthy subjects. Human peripheral mononuclear cells proliferated strongly in response to pig islet cells (p<0.001), though with notable interindividual variations (stimulation index 2 to 215). The variance of stimulation index was higher in diabetic than healthy subjects (p<0.0001). The response to islet cells was stronger (p<0.01) than that to pig splenocytes. Proliferation in response to islet cells was strongly decreased (p<0.01) when CD4+ T cells were blocked with monoclonal antibodies, whereas the blocking of CD8+ cells or NK cells gave less pronounced effects. The response to islet cells was decreased (p<0.01), but not abolished, after antigen-presenting cells were removed. Purified CD4+ cells alone did not proliferate in response to islet cells but recovered their proliferative ability when mixed with antigen-presenting cells, whereas CD8+ cells alone proliferated in the presence of interleukin-2 in response to islet cells. Proliferation was blocked (p<0.01) by anti-DR monoclonal antibodies. During proliferation in response to islet cells, interleukin-10 increased 43-fold (p<0.01) but interferon-gamma increased only slightly. No statistical differences were detected between diabetic and control subjects with respect to lymphocyte subsets and the recognition mechanisms or to interferon-gamma/interleukin-10 production in response to islet cells. These results provide the first detailed information on human cell-mediated xenoreaction to pig islet cells. This situation involves a dominant CD4 class II-restricted Th2 response, with an indirect recognition pathway, as well as a CD8 T-cell response resulting from direct recognition. This strong reaction constitutes a serious obstacle which may vary in degree among subjects.

Long-term culture of free or encapsulated islets isolated from specific pathogen-free (SPF) pigs

As the risk of recipient contamination is a limiting factor for xenotransplantation, the use of specific pathogen-free (SPF) pigs is mandatory. This study investigated the long-term culture of SPF pig islets and evaluated their insulin production when encapsulated in AN69 hollow fibres. Insulin secretion was studied after 3 weeks (n = 10), 2 months (n = 8) and 3 months (n = 3) by 45-min incubation in the presence of 2.8, 5.5, 11 and 16.5mM glucose. Although a decrease in the amount of secreted insulin occurred (1385 +/- 421 and 4323 +/- 1068 microns U/ml at 3 weeks for 2.8 and 16.5 mM glucose respectively; 702 +/- 261 and 2397 +/- 1047 microU/ml at 2 months; 59 +/- 23 and 154 +/- 34 microU/ml at 3 months), glucose-dependent insulin secretion was observed in all cases, i.e. stimulation indices of 8.1 +/- 3.1 (p < 0.05 vs the presence of 5.5 mM glucose) at 3 weeks, 3.3 +/- 1.1 at 2 months and 3.0 +/- 0.7 at 3 months. The insulin secretion of encapsulated SPF pig islets, cultured for 1 or 3 weeks, was evaluated under perifusion conditions using a stimulus of 10mM glucose plus 5.5 mM theophylline. Glucose stimulation resulted in a significant two-fold increase in insulin secretion (p < 0.05), which was maintained over culture time. These results indicate that SPF-isolated islets remained functional when cultured for several weeks either as free or encapsulated islets, although the magnitude of insulin secretion decreased dramatically after three months of culture.

Identification of cofilin, coronin, Rac and capZ in actin tails using a Listeria affinity approach

Actin assembly is involved in cell motility and intracellular movement of Listeria monocytogenes. Induction of Listeria actin tails is mediated by the surface protein ActA. The N-terminal domain of ActA is sufficient for this function. Cell components known to play a role in the actin-based motility of Listeria are VASP (vasodilatator-stimulated phosphoprotein), the multiprotein Arp2/3 complex and cofilin. VASP interacts with the central domain of ActA. Proteins interacting with the N-terminal domain of ActA have not been identified. To identify novel host cell components of ActA-induced actin tails, we used bovine brain extracts and an affinity approach with Listeria as matrix. Several known components of Listeria tails were isolated including VASP, Arp3 and cofilin. Cofilin was identified by peptide sequencing, and cofilin recruitment and Listeria tail length were found to be pH-dependent, in agreement with its recently reported role in enhancing actin filament turnover. In addition, three proteins not previously known to be associated with Listeria tails, coronin, Rac and capZ, were identified in our affinity approach. In infected cells, the localization of the identified proteins was studied by immunofluorescence. Our findings suggest that these latter proteins, which are known to play critical roles in cellular actin rearrangements, may also be involved in the dynamics of Listeria-induced actin assembly.

In vitro xenorecognition of adult pig pancreatic islet cells by splenocytes from nonobese diabetic or non-diabetes-prone mice

BACKGROUND

In vitro studies of the nonobese diabetic (NOD) mouse prone to type 1 autoimmune diabetes were conducted in order to investigate the mechanisms possibly involved in cell-mediated rejection of adult pig islet xenografts. Mouse cellular proliferation in discordant situations was previously investigated only with stimulator lymphocytes and found to be low in intensity and due to an indirect recognition mechanism involving murine antigen-presenting cells (APC). It was also important to characterize murine anti-pig islet response.

METHODS AND RESULTS

In the present study, mouse splenocytes responded to pig islet cells since primary proliferations were detected in non-diabetes-prone Balb/c (P<0.04) or NOD (P<0.001) mice. Moreover, NOD mice displayed a higher (P<0.003) splenocyte response to pig islet cells (stimulation index: 5.8+/-0.7) than did Balb/c mice (stimulation index: 2.3+/-0.3), whereas responses to pig stimulator splenocytes were similar in both strains. The proliferation of NOD splenocytes to pig islet cells was lower (P<0.0001) than the allogeneic response to Balb/c islet cells but similar to syngeneic proliferation to NOD islet cells. In both NOD and Balb/c mice, splenocyte proliferation to pig islet cells was abolished (P<0.01) when CD4+ cells were blocked with antibodies, whereas the blocking of CD8+ cells had a nonsignificant effect. The main T-splenocyte subsets involved were restricted to mouse MHC class II molecules as they did not proliferate in the presence of monoclonal antibodies directed at I-A molecules. NOD and Balb/c splenocyte proliferation to pig islet cells was abolished after removal of plastic-adherent APC, which indicates that the major activation pathway was indirect. Purified CD4+ or CD8- cells alone did not proliferate in response to pig islet cells but recovered a proliferative ability when mixed with APC. CD4- cells, alone or in the presence of APC, were not capable of responding to pig islet cells. Both Th1 and Th2 splenocytes were involved in response to pig islet cells since interferon-gamma (IFN-gamma) and interleukin (IL-)-4 production increased significantly (300-fold and 11-fold, respectively, P<0.02 for both), whereas the increase in IL-10 production was much lower (only 1.5-fold). The IFN-gamma/IL-4 and IFN-gamma/IL-10 ratios stimulated by pig islet cells were not different with NOD and Balb/c splenocytes.

CONCLUSION

In conclusion, mouse cell-mediated reaction against xenogeneic adult pig islet cells mainly involves class II-restricted CD4+ T lymphocytes of Th1 and Th2 subtypes, with an indirect pathway for the recognition. Although of low intensity, this cell-mediated reaction constitutes an obstacle to pig islet engraftment in the mouse, although one not necessarily more insurmountable than alloreactivity. The peculiarity of NOD mouse splenocytes, in terms of proliferation against pig islets, suggests that the study of islet xenograft rejection should take the immunogenetic context of diabetes into account, in which case the use of non-diabetes-prone mice has its limitations.

Spleen cells of non-obese diabetic mice fed with pig splenocytes display modified proliferation and reduced aggressiveness in vitro against pig islet cells

A new means of modifying xenogeneic reaction to pig islet cells, which involves pre-feeding with pig spleen cells, was investigated for the first time in the non-obese diabetic (NOD) mouse. Compared with controls, mice fed with pig spleen cells displayed much higher splenocyte proliferation in response to pig spleen and islet cells (p < 0.0001). This enhanced proliferation was specific for the species providing the fed cells. Positive relationships (p < 0.01) were found between increased splenocyte proliferation in response to pig spleen or islet cells and the number of cells per feeding or the number of daily feedings. Concomitantly, while co-incubation with splenocytes from control mice led to inhibition of both basal and stimulated insulin releases from pig islet cells (p < 0.001), this aggressiveness was abolished (p < 0.001) after co-culture with splenocytes from mice fed with pig spleen cells. The proliferative responses of splenocytes from fed or control mice to pig islet or spleen cells were abolished after removal of plastic-adherent cells, indicating that the major indirect pathway of T-cell activation was unchanged by pig spleen cell feeding. The main T-splenocyte subsets involved were restricted to MHC class II as they did not proliferate in the presence of monoclonal antibodies (mAbs) directed at I-A molecules. In mice fed with pig spleen cells, as well as in control mice, the blocking of CD4 + T cells with mAbs led to abolition of proliferation (p < 0.002), while the blocking of CD8 + led to a less marked effect. However, an increase in the blocking effect of anti-CD8 mAbs was noted in mice fed with pig spleen cells (p < 0.02). In control mice, the main splenocyte subset involved during proliferation in response to pig islet cells was Thl, since interferon gamma (IFNgamma) production increased significantly (p < 0.01) while that of interleukin-10 (IL-10) increased only slightly. The main change observed in mice fed with pig spleen cells was a marked increase in basal IL-10 production (p < 0.01) and the basal IL-10/IFNgamma ratio (p < 0.001). It seems likely that feeding with pig spleen cells shifted the Th1/Th2 balance towards a dominance of Th2-type class II-restricted CD4 + T cells, which may have been conducive to activating CD8 + suppressor T cells. In any event, oral administration of pig cells modified xenogeneic cellular response, which may have implications for xenografts of pig islets. In a more general sense, physiological feeding of cells from xenogeneic species would appear to have certain effects on the immune system.

Perifusion analysis of insulin secretion from specific pathogen-free large-white pig islets shows satisfactory functional characteristics for xenografts in humans

Though the pig appears to be the islet donor of choice for grafts in diabetic patients, there may be a risk of transmission of infectious agents. In this context, we adopted a strategy of islet isolation from pigs raised and killed in specific pathogen-free (SPF) conditions as a minimum with regard to the concept of quality assurance. Accordingly, the present study investigated the function of SPF pig islets to determine whether they react qualitatively and quantitatively to nutriments, hormones and neuromediators with which they would be confronted in man and could therefore provide effective regulation during physiologic or physiopathologic situations. beta cells from 18 Large-White SPF pigs were functionally intact after 7 days in culture. Insulin stimulation indexes (SI) of 3.1 +/- 0.2, 2.2 +/- 0.1, and 4.4 +/- 0.3 were found respectively for 30 mmol/l K+, 100 mumol/l tolbutamide and 10 mmol/l theophylline. Basal insulin secretion (72.2 +/- 7.6 muU/min) had already increased significantly (p < 0.001) with 5.5 mmol/l glucose (184.2 +/- 25.5 muU/min, SI: 2.5 +/- 0.6), indicating that the threshold stimulatory concentration was comparable to that of human islets. Insulin secretion increased in a glucose dose-dependent manner (p < 0.001): SI: 3.1 +/- 0.3 and 3.6 +/- 0.2 with 11.0 mmol/l and 22.0 mmol/l glucose, which showed a satisfactory magnitude with reference to human islets. Even the subtle phenomenon of "glucose memory" was apparent in these pig islets. Arginine stimulated (p < 0.001) insulin secretion dose-dependently (SI: 2.2 +/- 0.3 with 5 mmol/l and 2.9 +/- 0.2 with 10 mmol/l). The ketone body beta-hydroxybutyrate (10 mmol/l) also induced insulin secretion (SI: 4.3 +/- 0.3). Insulin release was stimulated by 4 mumol/l gastric inhibitory peptide, revealing sensitivity to the hormonal enteroinsular axis, and by 2 mumol/l glucagon. Parasympathetic cholinergic influence was studied using 500 mumol/l carbamylcholine, which increased insulin secretion. The influence of orthosympathetic control and of stress situations was also studied. As in human islet response, epinephrine and the alpha 2-agonist clonidine (50 mumol/l) inhibited insulin secretion. Finally pre-culture of islets may be beneficial for graft outcome, provided that no deterioration in islet function occurs. A prolonged 21-day culture of SPF pig islets showed no decrease in insulin response to glucose, arginine and potassium, even with an unaltered threshold stimulatory glucose concentration. Thus, Large-White SPF pigs and the application of our isolation procedure provided islets with functional characteristics reproducibly compatible with potential utilisation for effective regulation of glycaemia under physiologic and physiopathologic situations in humans.

Minimisation of microbial contamination for potential islet xenografts using specific pathogen-free pigs and a protected environment during tissue preparation

One major risk of islet xenotransplantation is transmission of infections. We thus compared microbial contamination during preparation of islets from 4 pigs conventionally breeded and slaughtered or 8 specific pathogen free (SPF) pigs, and different environmental conditions during pancreas excision. Pancreas harvested in a slaughterhouse (for conventional pigs) or in a protected autopsy room (for SPF pigs) were soaked in betadine solution and submitted to enzymatic digestion with collagenase. Islets were purified on histopaque gradient with a COBE 2991 processor. For each step of the process, a 10 ml aliquot was harvested and microbial contamination was analysed. For all animals, contamination of livers, which were not soaked in betadine solution, was also examined. Analysis of livers from the 4 conventional pigs showed polymicrobial contaminations (1,122 +/- 841 CFU/mg) with several species of Staphylococcus, Streptococcus, Bacillus and Enterobacteriaceae. For these conventional pigs, soaking of pancreas in betadine solution and presence of antibiotics in all media decreased the pancreatic contamination compared to hepatic contamination, but were unable to suppress it, as transport solution and crude suspension obtained after the digestion step with collagenase showed persistent contamination (9.7 +/- 2.4 and 10.5 +/- 4 CFU/ml, respectively). After islet purification by histopaque gradient, no medium remained contaminated. During analysis of the 8 SPF pigs, no liver exhibited contamination. Analysis of medium from each preparation step showed complete absence of contamination for 7 pancreases. Only one contamination with Staphylococcus simulans was observed for one pancreas in transport solution (6 CFU/ml), and persisted in digestion medium (16 CFU/ml). Finally, all purified suspensions were completely sterile. In conclusion, breeding conditions of pig islet donors, and controlled environment for pancreas excision, considerably influence the risk of microbial contamination. In order to limit the risk, SPF pigs are a suitable and compulsory source of islets.

The rpoN (sigma54) gene from Listeria monocytogenes is involved in resistance to mesentericin Y105, an antibacterial peptide from Leuconostoc mesenteroides

To gain insight into the mode of action of mesentericin Y105, a bacteriocin bactericidal agent against Listeria monocytogenes, we undertook to identify the listerial factors mediating this susceptibility by using a genetic approach. Transposon mutants resistant to the bacteriocin were obtained. One of them corresponded to a transposon insertion in a gene (rpoN) encoding a putative protein (447 amino acids) with strong homologies to alternative transcriptional sigma54 factors, including that of Bacillus subtilis (38% identity). Complementation experiments with the wild-type rpoN gene demonstrated that the insertion in rpoN was responsible for the resistance phenotype in L. monocytogenes. Moreover, expression of the L. monocytogenes rpoN gene in an rpoN mutant strain of B. subtilis promoted transcription of a sigma54-dependent operon in the presence of the associated regulator. These results demonstrate that the L. monocytogenes rpoN gene encodes a new sigma54 factor.

ActA is a dimer

ActA, a surface protein of Listeria monocytogenes, is able to induce continuous actin polymerization at the rear of the bacterium, in the cytosol of the infected cells. Its N-terminal domain is sufficient to induce actin tail formation and movement. Here, we demonstrate, using the yeast two-hybrid system, that the N-terminal domain of ActA may form homodimers. By using chemical cross-linking to explore the possibility that ActA could be a multimer on the surface of the bacteria, we show that ActA is a dimer. Cross-linking experiments on various L. monocytogenes strains expressing different ActA variants demonstrated that the region spanning amino acids 97-126, and previously identified as critical for actin tail formation, is also critical for dimer formation. A model of actin polymerization by L. monocytogenes, involving the ActA dimer, is presented.

Reversal of diabetes in non-obese diabetic mice by xenografts of porcine islets entrapped in hollow fibres composed of polyacrylonitrile-sodium methallylsulphonate copolymer

Intraperitoneal xenografting of islets immunoprotected by semipermeable membranes is a potential method of avoiding rejection by reversal of diabetes without immunosuppression. In this preliminary study, a xenograft of porcine islets, immunoprotected in semipermeable hollow fibres composed of a hydrogel of a polyacrylonitrile-sodium methallylsulphonate copolymer (AN 69), was used to reverse autoimmune insulin-dependent diabetes mellitus (IDDM) in the NOD mouse. A diabetic state was maintained in all 46 NOD mice which received transplants of empty fibres. Transplantation of encapsulated islets reversed the diabetic state in 37% (18/54) of the recipients. In these mice, nonfasting blood glucose concentration decreased within 24 h. Glycaemia was kept below the diabetic control range and the initial pretransplant value for 6 weeks. Recipient NOD mice suffered from the severe insulitis characteristic of clinical diabetes, confirming that reversal of the hyperglycaemic state was due solely to the xenografts. Pretransplant glycaemia was slightly (p < 0.05) higher in mice which remained diabetic after grafts of fibre-containing islets than in animals which experienced reversal of hyperglycaemia after transplantation) for the peritoneal cavity of recipients which had returned to normoglycaemia after grafting with islet-containing fibres. In all 4 cases, the islets responded to glucose during a perifusion assay. In 2 out of 4 grafts removed from mice which remained hyperglycaemic after grafting with islet-containing fibres (11, 13, 15 and 27 days after transplantation), no basal or stimulated insulin secretion was detectable. Histological sections of a total of 75 fibres retrieved from the peritoneal cavities of recipient NOD mice showed surrounding inflammation, with adherent cells, neovascularisation and fibrotic reaction. These preliminary results are promising for the continued development of this bioartificial pancreas for xenogeneic islet transplantation since they demonstrate that xenogeneic islets can survive in the autoimmune environment of the NOD mouse with spontaneous diabetes mimicking human IDDM).

[Spontaneous animal models for insulin-dependent diabetes (type 1 diabetes)]

Insulin dependent (type 1) diabetes in humans is a polygenic, auto-immune disease that is characterized, among other things, by the infiltration of the islets of Langerhans by immune cells (insulite) as well as many serum auto-antibodies (including islet cell antibodies: ICA). The medical goal is to diagnose the condition at a sub-clinical stage and then to prevent the disease from developing. Spontaneous diabetic rodent models, in particular the NOD mouse and BB rat are invaluable to the continuing progress of the work aimed at better understanding the human disease. In addition to these models, the study of type 1 diabetes in larger animals, having a longer life-span would also be helpful. In dogs and cats, certain minor kinds of diabetes appear to be of type 1. The classification of diabetes types in carnivores remains poorly defined, however, epidemiological, genetic and metabolic studies are required before these diabetes can be used as operational models for the human pathology. Even if the classification of these diseases is clarified, the ethical and social considerations involved with the use of companion animals, will limit the use of these animals as models for spontaneous diabetes. The selection of a specific line of diabetic dogs should perhaps be considered.

Identification of two regions in the N-terminal domain of ActA involved in the actin comet tail formation by Listeria monocytogenes

The ActA protein of Listeria monocytogenes induces actin nucleation on the bacterial surface. The continuous process of actin filament elongation provides the driving force for bacterial propulsion in infected cells or cytoplasmic extracts. Here, by fusing the N-terminus of ActA (residues 1-234) to the omega fragment of beta-galactosidase, we present the first evidence that this domain contains all the necessary elements for actin tail formation. A detailed analysis of ActA variants, in which small fragments of the N-terminal region were deleted, allowed the identification of two critical regions. Both are required to initiate the actin polymerization process, but each has in addition a specific role to maintain the dynamics of the process. The first region (region T, amino acids 117-121) is critical for filament elongation, as shown by the absence of actin tail in a 117-121 deletion mutant or when motility assays are performed in the presence of anti-region T antibodies. The second region (region C, amino acids 21-97), is more specifically involved in maintenance of the continuity of the process, probably by F-actin binding or prevention of barbed end capping, as strongly suggested by both a deletion (21-97) leading to 'discontinuous' actin tail formation and in vitro experiments showing that a synthetic peptide covering residues 33-74 can interact with F-actin. Our results provide the first insights in the molecular dissection of the actin polymerization process induced by the N-terminal domain of ActA.

Proteins spontaneously released by rat insulinoma (RIN) cells are anchored on cell membrane by a glycosyl-phosphatidyl-inositol link and inhibit increased RIN cell adhesion of lymphocytes from type 1 diabetic patients and non-obese diabetic mice in vitro

Our group previously reported an assay for the study of lymphocyte adhesion to insulin-producing cells in which xenogeneic rat insulinoma (RIN) cells were used as targets. The present study found an increased number of RIN-cytoadherent lymphocytes in 63 patients with Type 1 diabetes compared with 150 control subjects and in 211 NOD mice compared with 104 BALB/c mice (p < 0.001). Proteins concentrated from spontaneous RIN cell culture supernatants inhibited increased RIN-adhesion of NOD splenocytes or lymphocytes from diabetic patients (p < 0.001). In addition, increased RIN binding was dose-dependently abolished by RIN membrane extracts. The fact that RIN binding was inhibited by proteins from both membrane and the culture supernatant from RIN cells suggests that soluble inhibitory proteins were spontaneously released into the supernatant from a hydrophobic membrane-bound form. This tended to be confirmed since inhibition obtained with both preparations involved a 55-75 kDa HPLC protein fraction. The possibility that the membrane form of the inhibitory protein was anchored by a glycosylphosphatidylinositol (GPI) tail was evaluated. When RIN cells were treated with PI-PLC, their ability to bind lymphocytes from diabetic patients or NOD splenocytes decreased (p < 0.001) to control levels. Co-incubation with the 55-75 kDa fraction of proteins cleaved from RIN cells by PI-PLC also lowered the number of RIN-adherent NOD splenocytes to control levels. SDS-PAGE and IEF analyses of the 55-75 kDa inhibitory fraction from RIN cell supernatant revealed a major band with Mr 66 kDa and PI5.4, which may correspond to a protein with similar characteristics noted on 2-D electrophoresis of proteins cleaved from RIN cells by PI-PLC. Specific labelling of GPI moieties with 3H-ethanolamine, 3H-glucosamine, or 14C-glucosamine, as well as conversion of the hydrophobic Triton-X114 solubilised form into a hydrophilic form after PI-PLC treatment, confirmed the presence of a GPI anchor in this approximately 66 kDa RIN protein, which could thus be the molecule inhibiting adhesion in the system. Our data suggest that GPI-proteins from insulin-producing cells may influence the immune system both in their membrane-anchored and soluble forms. When considering the binding model, in which beta cells were tumoral and xenogeneic to diabetic lymphocytes, this potential influence of GPI-proteins suggests possible implications in situations of lymphocyte-beta cell interaction, i.e. anti-beta cell autoimmunity, immune reaction against insulinomas, and reaction against islet xenografts.

Prophylactic oral administration of metabolically active insulin entrapped in isobutylcyanoacrylate nanocapsules reduces the incidence of diabetes in nonobese diabetic mice

Nonobese diabetic (NOD) mice develop an autoimmune disease with a long prodromal period and constitute a model for investigating the prevention of human type 1 diabetes. Since prophylactic insulin injections reduced the incidence of diabetes in NOD mice, we tested a new prophylactic strategy to prevent diabetes in NOD mice consisting of oral administration of insulin, protected in polyalkylcyanoacrylate nanocapsules from degradation in the gastrointestinal tract. In humans, this form of prophylactic insulin administration would be less constraining than insulin injections. Ninety female NOD mice were randomized at weaning and fed once a week (from 60 to 300 days of age) with insulin nanocapsules (100 U/kg) or empty nanocapsules. Within the group fed with insulin nanocapsules, the incidence of diabetes was reduced (38% vs 75%; P < 0.02), the onset of disease was delayed (P < 0.02), and the severity of lymphocytic inflammation of endogenous islets was reduced (P < 0.03). Although the oral treatment was stopped at 300 days of age, the incidence of diabetes at 360 days remained lower in mice previously fed insulin nanocapsules (P < 0.02). Previous feedings with insulin nanocapsules did not protect against cyclophosphamide-induced diabetes, since final incidence of diabetes (sum of the incidence during the initial 360 days and the further CY-induced incidence) reached the final incidence obtained in mice previously fed empty nanocapsules and treated with cyclophosphamide. Intestinal absorption of insulin nanocapsules was evidenced by HPLC separation of human insulin in NOD sera. During cotransfer, T splenocytes from mice fed insulin nanocapsules were able to reduce the capacity of T cells from diabetic donors to adoptively transfer the disease (P < 0.01). Antigens for islet-cell autoantibodies (ICA) in pancreata from both NOD groups were compared by immunofluorescence with the same ICA-positive human sera to ensure that differences were due to quantitative changes in antigen. These antigens, which could serve as an index of a possibly more extended antigen beta-cell rest, were decreased (P < 0.02) and pancreatic insulin content was reduced (P < 0.05) in mice fed with insulin nanocapsules, suggesting a mechanism of 'beta cell rest'. To summarize, early feeding with insulin nanocapsules reduces diabetes and insulitis in the NOD mouse model that mimics human type 1 diabetes. This may be due both to generation of cellular mechanisms that actively suppress disease and a decrease in antigens which makes beta cells less vulnerable to autoimmune aggression.

Cyclosporin depresses pancreatic islet expression of antigens for islet cell autoantibodies in non obese diabetic mice

An unexpected observation led us to investigate whether a short course (7 days) of oral cyclosporin (CsA) at different doses (5, 10, 20 or 40 mg/kg/day) in nonobese diabetic (NOD) mice could modify the expression of islet antigens related to the autoimmune process. Analysis was performed on the last day of CsA administration, and then up to 60 days after CsA withdrawal. Antigen modulation was analysed by indirect immunofluorescence using islet-cell antibody (ICA)-positive human sera for ICA antigens, and by immunoperoxidase for glutamic acid decarboxylase 67 Kd (GAD67). Concomitantly, beta-cell function was evaluated by in vivo glucose tolerance and insulin response from isolated islets. The severity of insulitis and histological damage to islets was quantified. We measured splenocyte and thymocyte subsets by cytofluorometry (CD4+ CD8-, CD4- CD8+, and double-positive thymocytes; Thy1-2+, CD3+, CD4+, and CD8+ spleen cells) and determined splenocyte mitogenesis in response to concanavalin A. Even when the lowest dose (5 mg/kg) was used, CsA concentrated in the islets. A graded reduction of ICA antigens was detected, showing no effect for 5 mg/kg/day but a significant dose-dependent reduction (P < 0.01) with 10, 20 and 40 mg/kg/day. GAD67 expression was also reduced (P < 0.03) in a CsA dose-dependent manner. On the other hand, only treatment with the highest CsA dose (40 mg/kg/day) induced glucose intolerance in vivo (P < 0.02), decreased insulin sensitivity to glucose from isolated islets (P < 0.03), reduced insulitis (P < 0.03), and altered thymocyte and splenocyte phenotypes and mitogenesis (P < 0.02). Moreover, the reversibility of the different effects was different: islet antigens were not completely recovered 2 months after CsA withdrawal, whereas other immunologic and metabolic effects obtained with the highest CsA dose were reversed within 15 days. Thus, a short course of low CsA doses in NOD mice produced a pancreatic concentration of the drug which reduced the expression of certain islet antigens for several weeks, whereas major effects on immunological parameters and islet insulin release occurred only with higher CsA doses and improved more rapidly.

The amino-terminal part of ActA is critical for the actin-based motility of Listeria monocytogenes; the central proline-rich region acts as a stimulator

The intracellular bacterial pathogen Listeria monocytogenes moves inside the host-cell cytoplasm propelled by continuous actin assembly at one pole of the bacterium. This process requires expression of the bacterial surface protein ActA. Recently, in order to identify the regions of ActA which are required for actin assembly, we and others have expressed different domains of ActA by transfection in eukaryotic cells. As this type of approach cannot address the role of ActA in the actin-driven bacterial propulsion, we have now generated several L. monocytogenes strains expressing different domains of ActA and analysed the ability of the different domains to trigger actin assembly and bacterial movement in both infected cells and cytoplasmic extracts. We show here that the amino-terminal part is critical for F-actin assembly and movement. The internal proline-rich repeats and the carboxy-terminal domains are not essential. However, in vitro motility assays have demonstrated that mutants lacking the proline-rich repeats domain of ActA moved two times slower (6+/-2 micrometers min(-1)) than the wild type (13 +/-3 micrometers min(-1)). In addition, phosphatase treatment of protein extracts of cells infected with the L. monocytogenes strains expressing the ActA variants suggested that phosphorylation may not be essential for ActA activity.

The unrelated surface proteins ActA of Listeria monocytogenes and IcsA of Shigella flexneri are sufficient to confer actin-based motility on Listeria innocua and Escherichia coli respectively

Listeria monocytogenes and Shigella flexneri are two unrelated facultative intracellular pathogens which spread from cell to cell by using a similar mode of intracellular movement based on continuous actin assembly at one pole of the bacterium. This process requires the asymmetrical expression of the ActA surface protein in L. monocytogenes and the IcsA (VirG) surface protein in S. flexneri. ActA and IcsA share no sequence homology. To assess the role of the two proteins in the generation of actin-based movement, we expressed them in the genetic context of two non-actin polymerizing, non-pathogenic bacterial species, Listeria innocua and Escherichia coli. In the absence of any additional bacterial pathogenicity determinants, both proteins induced actin assembly and propulsion of the bacteria in cytoplasmic extracts from Xenopus eggs, as visualized by the formation of characteristic actin comet tails. E. coli expressing IcsA moved about two times faster than Listeria and displayed longer actin tails. However, actin dynamics (actin filament distribution and filament half-lives) were similar in IcsA- and ActA-induced actin tails suggesting that by using unrelated surface molecules, L. monocytogenes and S. flexneri move intracellularly by interacting with the same host cytoskeleton components or by interfering with the same host cell signal transduction pathway.

iactA of Listeria ivanovii, although distantly related to Listeria monocytogenes actA, restores actin tail formation in an L. monocytogenes actA mutant

A gene homologous to the actA gene of Listeria monocytogenes was cloned from Listeria ivanovii (strain CLIP257) by chromosome walking starting from the ilo gene that encodes the pore-forming toxin ivanolysin. The nucleotide sequence revealed that this gene, named iactA, encodes a protein of 1,044 amino acids (IactA) comprising a central region with seven highly conserved tandem proline-rich repeats of 47 amino acids. Although IactA and ActA share an overall similar structure, these two proteins are only distantly related. Like ActA, IactA migrates aberrantly on sodium dodecyl sulfate gels. When expressed in an L. monocytogenes actA deletion mutant strain, iactA restored actin polymerization.

Targeting of Listeria monocytogenes ActA protein to the plasma membrane as a tool to dissect both actin-based cell morphogenesis and ActA function

Actin assembly on the surface of Listeria monocytogenes in the cytoplasm of infected cells provides a model to study actin-based motility and changes in cell shape. We have shown previously that the ActA protein, exposed on the bacterial surface, is required for polarized nucleation of actin filaments. To investigate whether plasma membrane-associated ActA can control the organization of microfilaments and cell shape, variants of ActA, in which the bacterial membrane signal had been replaced by a plasma membrane anchor sequence, were produced in mammalian cells. While both cytoplasmic and membrane-bound forms of ActA increased the F-actin content, only membrane-associated ActA caused the formation of plasma membrane extensions. This finding suggests that ActA acts as an actin filament nucleator and shows that permanent association with the inner face of the plasma membrane is required for changes in cell shape. Based on the observation that the amino-terminal segment of ActA and the remaining portion which includes the proline-rich repeats cause distinct phenotypic modifications in transfected cells, we propose a model in which two functional domains of ActA cooperate in the nucleation and dynamic turnover of actin filaments. The present approach is a new model system to dissect the mechanism of action of ActA and to further investigate interactions of the plasma membrane and the actin cytoskeleton during dynamic changes of cell shape.

The virulence gene cluster of Listeria monocytogenes is also present in Listeria ivanovii, an animal pathogen, and Listeria seeligeri, a nonpathogenic species

Most known Listeria monocytogenes virulence genes cluster within a 9.6-kb chromosomal region. This region is flanked on one end by two uncharacterized open reading frames (ORF A and ORF B) and ldh, an ORF presumably encoding the L. monocytogenes lactate dehydrogenase (J.-A. Vazquez-Boland, C. Kocks, S. Dramsi, H. Ohayon, C. Geoffroy, J. Mengaud, and P. Cossart, Infect. Immun. 60:219-230, 1992). We report here that the other end is flanked by prs, and ORF homologous to phosphoribosyl PPi synthetase genes. ORF B and prs were detected in all Listeria species and thus delimit the virulence region. This virulence gene cluster was detected exclusively in hemolytic Listeria species, Listeria ivanovii, an animal pathogen, and Listeria seeligeri, a nonpathogenic species.

Neonatal injections of cyclosporin enhance autoimmune diabetes in non-obese diabetic mice

Since the modulation of the immune system at birth may influence the course of insulin-dependent (type 1) diabetes, we investigated whether neonatal injections of cyclosporin (CsA) to newborn non-obese diabetic (NOD) mice influence diabetes during later life. Two groups of 90 mice (45 female, 45 male) were injected intraperitoneally for the first 6 days of life with CsA (10 mg/kg per day) or with vehicle. In female NOD mice, the onset of diabetes was earlier and cumulative incidence was higher after neonatal treatment with CsA (P < 0.01). The incidence of diabetes was also dramatically enhanced in male NOD mice (P < 0.01), which normally display a very low disease incidence. Concomitantly, the severity of lymphocytic infiltration of the pancreatic islets was higher in female NOD mice neonatally treated by CsA (P < 0.02), and to a lesser extent in males, than in control mice. After administration of CsA to newborn NOD mice, there was a reduction (P < 0.01) of both CD4+CD8- and CD4-CD8+ thymocytes, whereas the number of double positive CD4+CD8+ thymocytes was increased. Concomitantly, Thy1-2+ cells in spleen were decreased (P < 0.01), and spleen cells expressing either CD3 molecule or alpha beta TCR complex were diminished (P < 0.01). Both CD4+ and CD8+ spleen T cells were depleted. By contrast, the low percentage of gamma delta TCR-expressing splenocytes was not modified. Numbers of MHC class 1+ or MHC class 2+ spleen cells were also depressed (P < 0.01). After neonatal injections of CsA, spleen cells showed a reduced response to concanavalin A (Con A) (P < 0.01). On the contrary, stimulation indices of splenocytes incubated with xenogeneic insulin-producing cell extracts were enhanced (P < 0.03). Proliferation indices of splenocytes to self class 2 antigens, generating suppressor cell activity, during syngeneic mixed lymphocyte reaction (SMLR) were significantly reduced (P < 0.01). Irradiated NOD mice were used as recipients for spleen cells from CsA-neonatally treated NOD mice. They displayed enhanced insulitis 2 weeks after transfer, and diabetes was successfully produced by 1 month after transfer in 50% of the recipients. By contrast, NOD mice which received control syngeneic spleen cells remained normoglycaemic, with only moderate islet infiltration which would be expected of NOD mice of this age. Thus, neonatal injections of CsA markedly enhance diabetes in both female and male NOD mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Release of carcinoembryonic antigen from human tumor cells by phosphatidylinositol-specific phospholipase C: highly effective extraction and upregulation from LS-174T colonic adenocarcinoma cells

Carcinoembryonic antigen (CEA), produced by gastrointestinal tumor cells, is anchored to cell membrane by a glycosyl-phosphatidylinositol moiety which can be cleaved with phosphatidylinositol-specific phospholipase C (PI-PLC). We studied the extraction of CEA from living human colon carcinoma (LS-174T, HT-29, COLO-205, and HRT-18) and pancreatic carcinoma (CAPAN) cells by PI-PLC from Bacillus cereus. The total CEA content of LS-174T cells, quantitated by Triton X-114 extraction followed by radioimmunoassay or by immunohistochemistry, was 3.5-fold higher than that of other cells (P < 0.001). The spontaneous release of CEA from LS-174T cells into culture medium was also higher than from other cells (P < 0.001), reaching 620 ng/10(7) cells (approximately 28% of cellular content) after 24 h. Overall, living LS-174T cells were highly susceptible to CEA extraction by PI-PLC, which was dependent on PI-PLC dose and on treatment time, leading in optimal conditions to the solubilization of 4100 ng/10(7) cells after 24 h (approximately 75% of total CEA). After 24 h treatment at the highest PI-PLC dose, cell lines remained viable and growing, and membrane CEA expression was not exhausted but only reduced as compared to untreated cells. At the same time, the amount of CEA solubilized by PI-PLC exceeded the CEA reduction in membranes, suggesting that enzyme treatment increased CEA turnover. This was particularly true for LS-174T cells which maintained 54% of the expression of untreated cells, whereas the amount of CEA extracted by PI-PLC reached 190% of this expression. Growing LS-174T cells thus constitute an effective material for producing high quantities of CEA by PI-PLC cleavage, especially since these cells probably "regenerate" because of enhanced turnover during PI-PLC action, thus allowing continuous CEA production. These experimental conditions also provide an interesting model for studying the modulation of CEA expression and release.

L. monocytogenes-induced actin assembly requires the actA gene product, a surface protein

The intracellular pathogenic bacterium L. monocytogenes can spread directly from cell to cell without leaving the cytoplasm. The mechanism of this movement, generated through bacterially induced actin polymerization, is not understood. By analyzing an avirulent Tn917-lac mutant defective for actin polymerization, we have identified a bacterial component involved in this process. The transposon had inserted in actA, the second gene of an operon. Gene disruption of downstream genes and transformation of the mutant strain with actA showed that the actA gene encodes a surface protein necessary for bacterially induced actin assembly. Our results indicate that it is a 610 amino acid protein with an apparent molecular weight of 90 kd.

Pleiotropic control of Listeria monocytogenes virulence factors by a gene that is autoregulated

Evidence for pleiotropic activation of virulence genes in Listeria monocytogenes is presented. A complementation study of a spontaneous prfA-deletion mutant and analysis of cassette and transposon insertion mutants showed that the gene prfA activates the transcription of four independent genes which code for a phosphatidyl-inositol-specific phospholipase C (gene plcA), listeriolysin O (gene hlyA), a metallo-protease (gene prtA) and a lecithinase (gene prtC). Transcription of prfA is not constitutive. During the growth phase, two peaks of prfA transcript accumulation were observed: the first was during exponential growth, and the second was at the beginning of the stationary phase. In addition, two prfA-specific transcripts of 2.2 kb and 1 kb are detected. Early in exponential growth, prfA is co-transcribed with plcA which lies upstream prfA, giving rise to the 2.2 kb plcA-prfA transcript. In late-exponential growth and at the beginning of the stationary phase, prfA transcripts of 1 kb are predominantly detected. Our results demonstrate that since prfA controls plcA transcription, it also regulates its own synthesis.

Entry of L. monocytogenes into cells is mediated by internalin, a repeat protein reminiscent of surface antigens from gram-positive cocci

We report the identification of a previously unknown gene, inlA, which is necessary for the gram-positive intracellular pathogen Listeria monocytogenes to invade cultured epithelial cells. The inlA region was localized by transposon mutagenesis, cloned, and sequenced. inlA was introduced into Listeria innocua and shown to confer on this normally noninvasive species the ability to enter cells. Sequencing of inlA predicts an 80 kd protein, internalin. Two-thirds of internalin is made up of two regions of repeats, region A and region B, and the C-terminus of the molecule is similar to that of surface proteins from gram-positive cocci. Internalin has a high content of threonine and serine residues, and the repeat motif of region A has regularly spaced leucine residues. As evidenced by Southern blot analysis, inlA is part of a gene family. One of them is the gene situated directly downstream of inlA, called inlB, which also encodes a leucine-rich repeat protein.

Tumor cell biotransformation products of prostaglandin A1 with growth inhibitory activity

The growth inhibitory effect and the fate of prostaglandin A1 (10(-6) M) were followed in cultures of rat B104 neuroblastoma and C6 glioma cells. More than 40% and 85% of the drug were neither recognized by a prostaglandin A1 antiserum nor extracted from the acidified medium with ethyl acetate, after 6 h and 24 h-incubation, respectively. When the supernatant of cells cultured in the presence of prostaglandin A1 during 24 hours was transferred to other cells and used as culture medium, the same growth inhibitory effect as with prostaglandin A1 was observed even when no prostaglandin A1 was added. After extensive purification and reverse phase HPLC of supernatant, four peaks more polar than prostaglandin A1 were shown; two of them were still active as growth inhibitors. This biotransformation was not observed with normal cells like L 929 or chick embryo fibroblasts, for which prostaglandin A1 had no inhibitory effect. The identification of these metabolites will allow the study of the structure-activity relationship.

Growth hormone-releasing factor (GRF) stimulates PGE2 production in rat anterior pituitary. Evidence for a PGE2 involvement in GRF-induced GH release

Rat anterior pituitaries were incubated over a 3-h period. Both PGE2 and GH were increased by GRF in a concentration-related manner (ED50: 3.5 nM and 6.5 nM, respectively). A significant correlation (r = 0.88, n = 127) was observed between GH and PGE2 release over the range of GRF concentrations tested. Among the five prostanoids analyzed, only PGE2 was selectively increased. Somatostatin lowered GH release, without any effect on PGE2 production. Indomethacin (Id) and Aspirin reduced significantly PGE2 synthesis and GRF-induced GH release. The inhibitory effect of Id was counteracted by addition of PGE2 to the medium. GRF and PGE2, at maximal concentrations, had a partial additive effect on GH release. The increase in PGE2 production and the reduced GH release in the presence of cyclooxygenase inhibitors suggest that PGE2 is involved in GRF-induced GH release.