"Tolerosomes" are produced by intestinal epithelial cells

The development of immunological tolerance to orally fed antigens depends on the sampling, processing and transportation events followed in the intestinal epithelium. We present here a description of a "tolerosome": a supra-molecular, exosome-like structure assembled in and released from the small intestinal epithelial cell. The tolerosome is a approximately 40 nm large vesicular structure that carries MHC class II (MHC II) with bound antigenic peptides sampled from the gut lumen. Tolerosomes isolated from serum shortly after antigen feeding or from an in vitro pulsed intestinal epithelial cell line are fully capable of inducing antigen specific tolerance in naive recipient animals. Purified tolerosomes represent a structure by which fed antigens can be efficiently presented to the immune system. Removal of the tolerosomes from serum by ultracentrifugation or absorption of MHC II results in abrogated tolerance development.

Immune defense mechanisms of the dental pulp

Defense reactions of the dentin/pulp complex involve a variety of biological systems, in which the immune system plays a pivotal role. The knowledge of the organization and function of pulpal immunocompetent cells has been sparse, but in recent years a significant body of information of immune mechanisms in general has provided a footing for substantial new knowledge of the immune mechanisms of the dental pulp. The identification of pulpal dendritic cells (DCs) has generated research activities which have led to a concept of how an antigenic challenge may evoke a pulpal inflammatory response. Although DCs are not able to identify foreign antigens specifically, they provide necessary signals to activate T-lymphocytes which in turn will orchestrate other immunocompetent cells to mount the local immune defense of the dental pulp. The purpose of this review is to accent the organization and function of pulpal DCs and other tissue and cellular components and to provide a basis for how they may interact to instigate pulpal defense mechanisms.

Influence of oestrogen receptor alpha and beta on the immune system in aged female mice

Oestrogen has a dichotomous effect on the immune system. T and B lymphopoiesis in thymus and bone marrow is suppressed, whereas antibody production is stimulated by oestrogen. In this study the importance of the oestrogen receptors (ER) ER-alpha and ER-beta in the aged immune system was investigated in 18 months old-wild type (WT), ER-alpha (ERKO), ER-beta (BERKO) and double ER-alpha and ER-beta (DERKO) knock-out mice, and compared with 4 months old WT mice. Cell phenotypes in bone marrow, spleen and thymus, and the frequency of immunoglobulin (Ig) spot forming cells (SFC) were determined. We show here that the 17-beta-oestradiol (E2)-induced downregulation of B lymphopoietic cells in bone marrow of young ovariectomized mice can be mediated through both ER-alpha and ER-beta. However, only ER-alpha is required for the age-related increased frequency of immunoglobulin M (IgM) SFC in the bone marrow, as well as for the increased production of interleukin-10 (IL-10) from cultured splenocytes in aged mice. Furthermore, increased age in WT mice resulted in lower levels of both pro- and pre-B cells but increased frequency of IgM SFC in the bone marrow, as well as increased frequency of both IgM and IgA SFC in the spleen. Results from this study provide valuable information regarding the specific functions of ER-alpha and ER-beta in the aged immune system.

Mucosal immunity

Mucosal defense is provided by a number of host factors countering the specific virulence factors of the many microorganisms infecting the mucous membranes. Secretory IgA antibodies presumably play an important role. Increase of the sIgA antibodies may most advantageously be attained by parenteral immunization, following mucosal priming. This was demonstrated in a rat model, where it was also noted that antigen injection into PP induced high milk IgA antibody levels. In man, parenteral vaccination against polio increased the sIgA antibody levels in the milk of mothers previously exposed naturally to the poliovirus. The response was relatively short-lived. In the previously unexposed, there was little or no response. By contrast peroral immunization with live poliovirus vaccine did not increase, or even decrease, the milk sIgA poliovirus antibody levels. Although salivary sIgA antibodies against antigens of colonizing E. coli appear during the first days of life, they are slow to increase. This deficiency is richly compensated for by all the sIgA antibodies that are provided the baby through the milk. No transfer of dimeric IgA into the milk could be shown in lactating rats, in contrast to what has been reported in mice. There is no evidence for a contribution to milk sIgA from serum in man. Close to parturition, human milk often contains some 7S IgA and various sizes of free SC, in addition to the dominating 11S sIgA. A few days later there is almost exclusively monomeric SC and 11S sIgA. IgG antibodies also play a role at the mucosal level. IgG2 antibodies against the bacterial polysaccharide capsule are as slow to appear as sIgA in ontogeny, possibly explaining the prevalence of infections with encapsulated bacteria and the poor response to polysaccharide vaccines in early childhood. Other defense factors preventing infections by way of mucous membranes may be important. Thus, oligosaccharides present in human milk seem to specifically prevent pneumococcal attachment to retropharyngeal cells. This anti-attachment capacity, in addition to that provided by milk and salivary IgA antibodies, may explain why breast-fed babies have less otitis media than formula-fed ones.

Loss of ileal IgA+ plasma cells and of CD4+ lymphocytes in ileal Peyer's patches of vitamin A deficient rats

Child mortality in diarrhoeal disease is increased significantly by vitamin A deficiency in poor countries. The pathological mechanisms are not known in detail. However, in this paper we report that vitamin A-deficient Wistar rats had much reduced IgA+ plasma cells in the ileal lamina propria (eightfold reduction from 470 cells/mm(2), P = 0.009), as well as a prominent reduction of CD4+ cells in the parafollicular regions of ileal Peyer's patches (reduction from 7200 to 105 cells/mm(2), P = 0.009). IL-2Ralpha-chain (CD25) positive lymphocytes in the ileal Peyer's patches were also reduced significantly in vitamin A deficiency (from 1400 to 300 cells/mm(2), P = 0.009). The density of CD8 cells tended to be increased relative to the control animals (from 5100 to 6000 cells/mm(2), not statistically significant). In conclusion, the marked decrease of lamina propria IgA+ plasma cells may be one cause of the high diarrhoeal mortality in vitamin A deficiency. This, in turn, appears to be related to reduced numbers of activated or regulatory CD4+ T cells in Peyer's patches.

Dimeric IgA in the rat is transferred from serum into bile but not into milk

Intravenous administration of ductus thoracicus lymph with dimeric IgA antibodies against Escherichia coli 06 to lactating rat dams did not result in transfer of IgA antibodies into the milk, although the antibodies were detectable in serum 1 min after the administration and in bile 60 min later. After intravenous injection of serum from bile-duct-occluded (BDO) rats immunized in the Peyer's patches into lactating rat dams. IgA antibodies appeared in the serum and remained there up to 230 min. At this time no IgA antibodies were seen in the milk while they were present in bile. IgG and IgM 06 antibodies did not appear in bile or milk after intravenous administration of lymph or serum from BDO rats.

Structural and functional association between substance P- and calcitonin gene-related peptide-immunoreactive nerves and accessory cells in the rat dental pulp

Defense mechanisms of the dentin/pulp complex involve a variety of biological systems in which immunocompetent cells, the nervous system, and the vascular supply play important roles. In the present study, pulpal accessory cells were examined regarding (i) their structural relationship to nerves and (ii) how the functional capacities of these cells were affected by neuropeptides. Micro-anatomic association was investigated in the normal rat molar pulp with the use of double-immunofluorescence staining and dual-channel confocal laser scanning microscopy. Examinations of confocal laser scanning microscopic images from single focal planes revealed the presence of apparent contacts between thin, varicose nerve fibers and immunocompetent cells, indicating proximity between these two structures. The close associations were most frequently observed in the para-odontoblastic region of the coronal pulp, where more than 70% of class II antigen-expressing (OX6+) cells showed proximity to nerve fibers immunoreactive to calcitonin gene-related peptide. The corresponding figure for substance P was about 50%. ED2+ macrophages closely associated with nerves were less frequently observed. Functional studies conducted in vitro demonstrated that 10(-9) to 10(-7) mol/L of substance P significantly increased (p < 0.05), while 10(-7) to 10(-6) mol/L of calcitonin gene-related peptide suppressed (p < 0.01) proliferation of purified T-lymphocytes stimulated with sub-optimal concentrations of concanavalin A in the presence of rat incisor pulpal cells as accessory cells. These data suggest that pulpal sensory nerve fibers and their products may have an influence upon the immune defense of the dental pulp.

Effects of root canal sealers on immunocompetent cells in vitro and in vivo

Over the years of testing biocompatibility of endodontic filling materials, little attention has been paid to the potential adverse influences on the function of the immune system. Therefore, the purpose of this study was to investigate the extent to which extractable components of some commonly used root canal sealing materials (ERCS) may interfere with immunocompetent cells in vitro. The potential of these materials to cause delayed-type hypersensitivity (DTH) was also addressed in a rat model system. Extractable components were drawn in cell culture medium from freshly mixed or set material of AH 26. Grossman's sealer, Endomethasone, and Apexit. In-vitro assays included either spleen cells or rat pulp tissue cells that were released following enzymatic digestion with collagenase. Purified T cells for the pulpal cell assay were obtained from rat mesenteric lymph nodes. The effect of ERCS on the proliferation of concanavalin A (con A) stimulated spleen cell was measured by 3H-thymidine incorporation. Pulpal accessory cell function was monitored by the capacity of pulpal cells, pretreated with components of ERCS, to provide signals to con A stimulated T cells. DTH was tested after subcutaneous implantation of root canal sealers (RCS) in rats and challenge by ear injection. Pretreatment of pulpal cells with low dilutions of eluates from extracted AH 26 and Endomethasone resulted in a strong reduction of the T cell proliferation rate. The effect was considerably reduced (P < 0.01) when extracts of the solid material were employed. Extracts of Grossmans' sealer and Apexit affected T cell proliferation only to a limited extent in the pulpal cell assay. In general, assays on spleen cells showed a similar profile, although increased cell division was induced by Grossman's sealer at high eluate dilutions and a concentration-dependent decrease of cell division at lower concentrations of this material. ERCS evoked both immunosuppression and, in some instances, immunostimulation, but they did not release DTH.

Hydrogen sulfide exposure induces NLRP3 inflammasome-dependent IL-1β and IL-18 secretion in human mononuclear leukocytes in vitro

The aim was to investigate if hydrogen sulfide (H₂S) induces the formation of the NLRP3 inflammasome and subsequent IL‐1β and IL‐18 secretion in human peripheral blood mononuclear cells (PBMCs) and in the human monocyte cell line THP1. Bacterial production of H₂S has been suggested to participate in the inflammatory host response in periodontitis pathogenesis. H₂S is a toxic gas with pro‐inflammatory properties. It is produced by bacterial degradation of sulfur‐containing amino acids, for example, cysteine. We hypothesize that H₂S affects the inflammatory host response by inducing formation of the NLRP3 inflammasome and thereby causes the secretion of IL‐1ß and IL‐18. PBMCs from eight healthy blood donors, the human monocyte cell line THP1 Null, and two variants of the THP1 cell line unable to form the NLRP3 inflammasome were cultured in the presence or absence of 1 mM sodium hydrosulfide (NaHS) in 24‐well plates at 37°C for 24 hr. Supernatants were collected and the IL‐1β and IL‐18 concentrations were measured with DuoSet ELISA Development kit. PBMCs exposed to NaHS produced more IL‐1ß and IL‐18 than unexposed control cells (p = .023 and p = .008, respectively). An increase of extracellular potassium ions (K⁺) inhibited the secretion of IL‐1ß and IL‐18 (p = .008). Further, NaHS triggered the secretion of IL‐1ß and IL‐18 in human THP1‐Null monocytes (p = .0006 and p = .002, respectively), while the NaHS‐dependent secretion was reduced in the monocyte cell lines unable to form the NLRP3 inflammasome. Hence, the results suggest that NaHS induces the formation of the NLRP3 inflammasome and thus the secretion of IL‐1ß and IL‐18. Enhanced NLRP3 inflammasome‐dependent secretion of IL‐1β and IL‐18 in human mononuclear leukocytes exposed to NaHS in vitro is reported. This may be a mode for H₂S to contribute to the inflammatory host response and pathogenesis of periodontal disease.

Antigen presenting capacity of Langerhans cells from rat oral epithelium

The ability of Langerhans cells (LC) from rat oral mucosa to internalize and process antigens and to participate in the induction of T cell mitogenesis was examined. To purify LC from epithelial cells, monoclonal anti-class II antibodies and immunomagnetic beads were employed. Suspensions of epithelial cells, containing LC, were found to be effective in mediating a Con A-induced T cell proliferation. Depletion of class II molecule-expressing LC reduced the proliferation of T cells by 80%. Presentation of ovalbumin (OA) to primed T cells was found to be dependent on the concentration of OA and the number of LC. Partially purified LC were five times as effective in inducing proliferation of primed T cells as the untreated suspension of epithelial cells. The data suggest that LC obtained from rat oral mucosa can generate accessory signals, process antigens and serve as antigen-presenting cells.

CD4+CD25+ T lymphocytes in human tonsils suppress the proliferation of CD4+CD25- tonsil cells

Animal studies define CD4+CD25+ T cells as a subset that protect against autoimmune inflammation. We wanted to investigate whether CD4+CD25+ T cells from patients with recurrent tonsillitis could suppress the proliferation of other tonsil cells, in vitro, as this immunological tissue also may serve as a model for chronic inflammation. Tonsil CD4+CD25+ cells markedly suppressed the proliferation of CD4+CD25- T cells in Concanavalin A-stimulated cocultures compared with cultures containing CD4+CD25- T cells only. The suppression exerted by the CD4+CD25+ cells was abrogated if these cells were irradiated before coculture or if interleukin (IL)-2 was added to the culture medium. CD4+CD25+ T cells proliferated poorly in response to mitogen, when cultured alone. Substitution with CD4+CD25+ T cells isolated from peripheral blood, enriched by similar methods, did not downregulate the proliferation of CD4+CD25- responder cells from tonsils. The augmented suppressive ability of tonsil CD4+CD25+ T cells compared with cells of this phenotype from blood, on CD4+CD25- responder cells from tonsils, suggests that there may be a functional difference between CD25+ cells from the two locations. In conclusion, CD4+CD25+ T cells from inflamed tonsils distinctly suppressed T-cell responses to mitogen in vitro, pointing to a regulatory role for CD4+CD25+ cells retrieved from inflammatory reactions in humans.

IgA antibodies in rat bile are not solely derived from thoracic duct lymph

The IgA level in rat bile was significantly decreased by drainage of the thoracic duct, and passively administered IgA antibodies to Escherichia coli O antigen decreased similarly. In contrast, specific IgA antibodies against E. coli O antigen raised by immunization in the Peyer's patches did not diminish significantly in the bile. Rats immunized in the Peyer's patches with sheep erythrocytes had IgA-forming cells in the thoracic lymph nodes, in the mesenteric lymph nodes, and in the spleen. Perfusion of the liver of immunized animals significantly decreased the bile levels of the IgA antibodies. It seems that IgA antibodies reach the bile not only via the thoracic duct but also via lymph ducts originating from thoracic lymph glands and the spleen.

Defence of mucous membranes by antibodies, receptor analogues and non-specific host factors

Most infections reach man via the mucosal membranes, and more than half of the lymphoid system is found in connection with mucosae. The major antibodies found on mucous membranes are secretory IgA, which function primarily by binding microorganisms and thereby preventing their contact with the host tissues. The optimal mode of immunization to obtain a secretory IgA response is not well defined. Repeated mucosal exposure with antigen may result in oral tolerance, with decreasing circulating antibodies but a remaining secretory IgA response. The secretory IgA response is usually short-lived and can be difficult to boost. IgM as well as IgG antibodies may add to host defence at the mucosal level, but when engaged, they usually induce inflammation in host tissues. Analogues to bacterial receptors on mucosal epithelium may be present in exocrine secretions such as human milk. During an attack on the host, it is possible that such receptor analogues may aid in the prevention of attachment of bacteria to mucous membranes used as an initial site. A number of non-specific host factors support mucosal defence. One of them is lactoferrin. Lactoferrin deficiency seems to result in recurrent bacterial infections, suggesting its importance in normal host defence.

Inflammatory cytokine release is affected by surface morphology and chemistry of titanium implants

To investigate in vitro cellular cytokine expression in relation to commercially pure titanium discs, comparing a native surface to a fluorinated oxide nanotube surface. Control samples pure titanium discs with a homogenous wave of the margins and grooves and an often smeared-out surface structure. Test samples pure titanium discs with a fluorinated titanium oxide chemistry and surface morphology with nanopore/tube geometry characterized by ordered structures of nanotubes with a diameter of ≈ 120 nm, a spacing of ≈ 30 nm, and a wall thickness of ≈ 10 nm. Cross-section view showed vertically aligned nanotubes with similar lengths of ≈ 700 nm. Peripheral blood mononuclear leucocytes were cultured for 1, 3, and 6 days according to standard procedures. BioPlex Pro™ assays were used for analysis and detection of cytokines. Selected inflammatory cytokines are reported. A pronounced difference in production of the inflammatogenic cytokines was observed. Leucocytes exposed to control coins produced significantly more TNF-α, IL-1ß, and IL-6 than the test nanotube coins. The effect on the TH2 cytokine IL-4 was less pronounced at day 6 compared to days 1 and 3, and slightly higher expressed on the control coins. The morphology and surface chemistry of the titanium surface have a profound impact on basic cytokine production in vitro. Within the limitations of the present study, it seems that the fluorinated oxide nanotube surface results in a lower inflammatory response compared to a rather flat surface that seems to favour inflammation.

Different expression of IL-2 receptor alpha-chain on a lamina propria T cell population and goblet cells in rats orally tolerized or sensitized to ovalbumin (OA) after colonization with an OA-producing Escherichia coli

The aim of this study was to compare the local gut immune response in sensitized and orally tolerized experimental animals. The development of IgE/IgG antibodies and the DTH to OA was studied in rats made orally tolerant to OA and compared with sensitized control rats after colonization with an Escherichia coli genetically engineered to produce OA. At 3 weeks of age, pups were weaned onto a standard diet without OA or an OA-containing diet for 4 weeks and then switched to a standard diet without OA. Both groups of rats were parenterally immunized with a mixture of OA and human serum albumin (HSA) in Freund's complete adjuvant when they were 8 weeks old. After DTH measurement 2 weeks later, all rats were colonized with an E. coli producing OA for 5 days. The local immune response in the small intestine was assessed, using immunohistochemistry, as the expression of MHC class II molecules and IL-2 receptor (IL-2R) alpha-chain. The OA-tolerant rats showed the classical signs of oral tolerance, with a reduced IgE and IgG antibody and DTH response to OA before colonization. The difference between the two groups in the anti-OA antibody response became even more pronounced after colonization with the E. coli that produce OA. Rats orally tolerant to OA maintained a normal villus architecture after colonization, with a normal expression of MHC class II molecules similar to non-treated adult rats, but with a significantly higher (P = 0.004) expression of IL-2R alpha-chain on T cells in the lamina propria of the villus core compared with sensitized control rats. The tolerant rats showed a very weak staining with the anti-IL-2R alpha-chain-specific antibody on a few goblet cells in only one out of seven rats. In the sensitized control rats, a marked local immune response was seen with an intense staining with a monoclonal anti-IL-2R alpha-chain-specific antibody on goblet cells in five out of seven rats (P = 0.019) and also an increased expression of MHC class II molecules in the epithelial cells and cells in the lamina propria of all rats. Rats orally tolerant to OA maintained a normal villus architecture after colonization, but with a significantly higher (P = 0.004) expression of IL-2R alpha-chain on T cells in the lamina propria of the villus core compared with sensitized control rats. The novel finding that goblet cells express IL-2R alpha-chain and the striking difference in expression of the receptor and the numbers of goblet cells between tolerant and sensitized rats may suggest a direct T cell regulation of the goblet cells. A possibility that oral tolerance might be maintained by the activated T cells expressing IL-2R alpha-chain in the lamina propria of the villus core is also discussed.

Defence of mucous membranes by antibodies, receptor analogues and non-specific host factors

Most infections reach man via the mucosal membranes, and more than half of the lymphoid system is found in connection with mucosae. The major antibodies found on mucous membranes are secretory IgA, which function primarily by binding microorganisms and thereby preventing their contact with the host tissues. The optimal mode of immunization to obtain a secretory IgA response is not well defined. Repeated mucosal exposure with antigen may result in oral tolerance, with decreasing circulating antibodies but a remaining secretory IgA response. The secretory IgA response is usually short-lived and can be difficult to boost. IgM as well as IgG antibodies may add to host defence at the mucosal level, but when engaged, they usually induce inflammation in host tissues. Analogues to bacterial receptors on mucosal epithelium may be present in exocrine secretions such as human milk. During an attack on the host, it is possible that such receptor analogues may aid in the prevention of attachment of bacteria to mucous membranes used as an initial site. A number of non-specific host factors support mucosal defence. One of them is lactoferrin. Lactoferrin deficiency seems to result in recurrent bacterial infections, suggesting its importance in normal host defence.

Development of antigen-specific IgE after sensitisation with trimellitic anhydride in rats is attenuated by glucocorticoids and cyclosporin A

BACKGROUND

Trimellitic anhydride (TMA) is a low-molecular-weight compound capable of inducing occupational asthma in man. We have characterized the TMA-induced antibody responses in Brown-Norway rats (BNR) and evaluated the effects of treatment with the glucocorticoid betamethasone or with cyclosporin A (CsA) on this response.

METHODS

Animals were sensitised by two intradermal injections of 0.1 ml TMA suspended in corn oil, and development of specific antibodies was assessed using ELISA.

RESULTS

Both IgE and IgG anti-TMA antibodies started to rise between weeks 1 and 3 after immunisation, reached their highest levels 7 weeks after sensitisation with 3% of TMA and then started to decline. Betamethasone and CsA given orally over the time of sensitisation (8 days in total) inhibited the development of specific IgE and IgG anti-TMA antibodies. Betamethasone given 10-17 days after sensitisation attenuated the IgE and IgG antibody responses as well while treatment with CsA after sensitisation had no effect on the production of specific antibodies. Levels of total IgE and IgG were not affected except for a small decrease in total IgE using medium-dose betamethasone after sensitisation.

CONCLUSION

We conclude that TMA-sensitised BNR develop specific IgE and IgG anti-TMA antibodies, and that glucocorticoids and CsA attenuate this response.