Role of mucosal immunity in influenza

Adaptive humoral immunity mediated by secretory antibodies appears to be desirable in the defence against mucosal virus infections. Specific secretory immunoglobulin A (SIgA) can inhibit initial pathogen colonization by performing immune exclusion both on the mucosal surface and within infected secretory epithelial cells without causing tissue damage. Like natural infections, live topical vaccines or adequate combinations of inactivated vaccines and mucosal adjuvants give rise not only to SIgA antibodies, but also to longstanding serum IgG and IgA responses. The intranasal route of vaccine application appears particularly attractive to achieve this result. The degree of protection after vaccination may range from complete inhibition of re-infection to reduction of symptoms. In this scenario it is generally difficult to determine unequivocally the relative importance of SIgA versus serum antibodies. However, infection models in knockout mice support the notion that SIgA exerts a decisive role in protection and cross-protection against influenza.

Interferon-gamma-secreting T cells localize to the epithelium in coeliac disease

Increased levels of interferon-gamma (IFN-gamma) transcripts have previously been found in duodenal biopsy specimens from patients with untreated coeliac disease (CD). Such samples and duodenal control mucosa were therefore studied to locate and phenotype cells spontaneously secreting IFN-gamma. Specimens were collected from consecutively recruited patients with untreated (seven), treated (four) or refractory (three) CD and from five histologically normal controls. Morphological and immunohistochemical examinations were performed, and epithelial and lamina propria cell suspensions were prepared from parallel samples. Unstimulated viable cells secreting IFN-gamma were identified and phenotyped with a new fluorescence-activated cell sorter-based assay, and IFN-gamma messenger RNA (mRNA) was analysed in snap-frozen aliquots of the same suspensions. Untreated CD cases had the highest fraction of IFN-gamma+ cells in the epithelial compartment (median 2.6%, range 1.6-6.2%) and, less strikingly, in the lamina propria compartment (1.6%, range 0.3-3.6%), followed by refractory (1.4%, 1.0-1.9%; and 0.3%, 0.0-1.2%) and treated (0.8%, 0.5-0.9%; and 0.7%, 0.2-1.1%) disease and finally the controls (0.5%, 0.3-0.9%; and 0.2%, 0.1-0.7%). IFN-gamma mRNA data supported these findings. IFN-gamma+ intraepithelial lymphocytes were mostly CD3+ and CD8+, whereas many positive lamina propria cells were CD8-. We conclude that isolated T cells spontaneously secreting IFN-gamma localize preferentially in the epithelium of patients with classical and refractory CD.

Involvement of plasmacytoid dendritic cells in human diseases

In vitro studies have reported that plasmacytoid dendritic cells (PDCs) exert multiple functions, including production of interferon (IFN)-alpha as effector cells and regulation of T-cell responses as mature DCs. Here we review recent data obtained in situ showing that PDCs accumulate in lesions of type I IFN-related disorders (virus infections and lupus erythematosus), Th2 cell-dominated allergic reactions, and ovarian carcinoma. These results demonstrate that PDCs do migrate to peripheral tissues during inflammation, which lends further support to the view that PDCs most likely are important players in innate and adaptive immunity in vivo. Future research should aim at defining the exact pathogenic or defense roles of PDCs in such disorders and determine whether these cells are potential targets for therapeutic intervention in microbial infections, allergy, autoimmunity, or cancer.

CD38 is a marker of human lacteals

CD38 is a type II transmembrane glycoprotein involved in signaling and adhesion which is expressed mainly by immature hematopoietic cells and activated lymphoid cells. Central lymphatic channels of human small intestinal villi, the so-called lacteals, were coincidentally found to express CD38. Gastric and large intestinal mucosae, pancreas, liver, lung, nasal mucosa, kidney, thymus, palatine tonsil, Peyer's patches, appendix, and mesenteric lymph nodes, and rodent intestinal mucosa were subsequently examined for lymphatic expression of CD38. Cryosections prepared from biopsy or surgical resection specimens were immunostained with four different antibodies to CD38 combined with antibodies to von Willebrand factor and CD31 to differentiate lymphatics from blood vessels, or with antibody to lysosomal protein. Sections were evaluated by ordinary and confocal immunofluorescence microscopy. Jejunal cryosections were subjected to in situ hybridization for CD38. All CD38 antibodies decorated human lacteals, and some of these were positive for CD38 mRNA. Lymphatics draining Peyer's patches and appendix as well as afferent lymphatics of mesenteric lymph nodes expressed CD38 weakly. CD38 was not detected on lymphatics in other organs or in rodent lacteals. We propose that CD38 is a novel marker of human small intestinal lymphatic vessels.

The carboxyl-terminal domains of IgA and IgM direct isotype-specific polymerization and interaction with the polymeric immunoglobulin receptor

Mucosal surfaces are protected by polymeric immunoglobulins that are transported across the epithelium by the polymeric immunoglobulin receptor (pIgR). Only polymeric IgA and IgM containing a small polypeptide called the "joining" (J) chain can bind to the pIgR. J chain-positive IgA consists of dimers, and some larger polymers, whereas only IgM pentamers incorporate the J chain. We made domain swap chimeras between human IgA1 and IgM and found that the COOH-terminal domains of the heavy chains (Calpha3 and Cmu4, respectively) dictated the size of the polymers formed and also which polymers incorporated the J chain. We also showed that chimeric IgM molecules engineered to contain Calpha3 were able to bind the rabbit pIgR. Since the rabbit pIgR normally does not bind IgM, these results suggest that the COOH-terminal domain of the polymeric immunoglobulins is primarily responsible for interaction with the pIgR. Finally, we made a novel chimeric IgA immunoglobulin, containing the terminal domain from IgM. This recombinant molecule formed J chain-containing pentamers that could, like IgA, efficiently form covalent complexes with the human pIgR ectodomain, known as secretory component.

B cell attracting chemokine 1 (CXCL13) and its receptor CXCR5 are expressed in normal and aberrant gut associated lymphoid tissue

BACKGROUND AND AIMS

In mice, the B lymphocyte chemoattractant (BLC) CXC chemokine ligand 13 (CXCL13) is sufficient to induce a series of events leading to the formation of organised lymphoid tissue. Its receptor, CXCR5, is required for normal development of secondary lymphoid tissue. However, the human counterpart, B cell attracting chemokine 1 (BCA-1) has only been detected in the stomach and appendix and not in other parts of normal or diseased gut. Hence to elucidate the potential role of this chemokine and its receptor in human gut associated lymphoid tissue (GALT), we analysed their expression in normal intestine and ulcerative colitis (UC).

METHODS

Frozen sections of surgical specimens were studied by multicolour immunofluorescence staining, in situ mRNA hybridisation, and reverse transcription-polymerase chain reaction.

RESULTS

BCA-1 mRNA was detected in all normal colonic and UC specimens. BCA-1 was produced and accumulated in relation to peripheral dendritic elements of lymphoid follicles in Peyer's patches and normal colon, as well as in irregular lymphoid aggregates in UC lesions. BCA-1 was partially associated with the traditional follicular dendritic cell phenotype but also with extracellular fibrils in GALT structures. CXCR5 protein was expressed by mantle zone B cells and appeared at a high level on scattered germinal centre T cells.

CONCLUSIONS

BCA-1 and CXCR5 are expressed in normal GALT structures as well as in irregular lymphoid aggregates in UC. This strongly suggests that BCA-1 plays an important role not only in the formation of normal GALT but also in the generation of aberrant lymphoid tissue in inflammatory bowel disease.

Heterogeneity of intraepithelial lymphocytes in refractory sprue: potential implications of CD30 expression

BACKGROUND

Refractory sprue is defined as primary or secondary failure to respond to a gluten free diet in patients with coeliac disease-like enteropathy and may signify cryptic or overt enteropathy associated T cell lymphoma.

AIMS

To study in detail jejunal morphology and immunophenotypes in patients with refractory sprue in the search for features that might be useful to predict prognosis.

PATIENTS

Seven patients are described, representing all such cases identified in our hospital over a 13 year period.

METHODS

Biopsy and/or surgical resection specimens were examined by morphology, immunohistochemistry, including enzymatic and immunofluorescent detection, and molecular biology.

RESULTS

All patients had phenotypically abnormal intraepithelial lymphocytes (IELs) that lacked CD8, T cell receptor alpha beta (or gamma delta), and/or expressed CD30 in addition to variable expression of the natural killer cell receptor CD94. A monoclonal T cell population was present in six cases, data from the seventh being inconclusive. Three patients had overt lymphoma with CD30+ tumour tissue intervening between intact mucosa that contained neoplastic IELs. Intriguingly, CD30+ IELs were observed both a long way away from, and in direct continuity with, the tumours in these patients. Such CD30+ cells were hardly detected in patients without tumours, two of which are in good health several years after the initial diagnosis.

CONCLUSIONS

Our data suggest that abnormal IELs in patients with refractory sprue are phenotypically heterogeneous. CD30 expression by these cells may indicate a worse prognosis, including the occurrence of overt lymphoma.

IgVH gene analysis suggests that peritoneal B cells do not contribute to the gut immune system in man

The contribution of peritoneal B cells to the intestinal lamina propria plasma cell population is well documented in mice, but unknown in humans. We have analyzed immunoglobulin (Ig) genes of human peritoneal B cells, because such genes show distinctive characteristics in mucosal B cells, particularly highly mutated variable regions. Here, we report the characteristics of variable region genes used by IgM, IgA and IgG in peritoneal cells. We focused on the properties of IgV(H)4-34 to allow comparisons of like-with-like between different isotypes and cells from different immune compartments. We observed that the IgM genes were mostly unmutated, and that the mutated subset had less mutations than would be expected in a mucosal B cell population. Likewise, the IgV(H)4-34 genes used by IgA and IgG from peritoneal B cells had significantly lower numbers of mutations than observed in the mucosal counterparts. Other trends observed, while not reaching statistical significance, followed the trend of peripheral B cells. The peritoneal B cell population had more IgA1 than IgA2 sequences, and there was no dominance of J(H)4 in the IgA from peritoneum or spleen, in contrast to the mucosal sequences. Overall, this study suggested that human peritoneal B cell are either peripheral or mixed in origin; they are unlikely to represent an inductive compartment for the mucosal B cell system.

Vascular morphogenesis and differentiation after adoptive transfer of human endothelial cells to immunodeficient mice

To establish a model for adoptive transfer of endothelial cells, we transferred human umbilical vein endothelial cells (HUVECs) to immunodeficient mice (Rag 2(-/-)). HUVECs were suspended as single cells in Matrigel and injected subcutaneously in the abdominal midline. Within 10 days after injection, HUVECs expressed pseudopod-like extensions and began to accumulate in arrays. By day 20, we observed human vessels that contained erythrocytes, and on day 30 we observed perivascular cells that expressed smooth muscle actin, thus resembling mature vessels. Throughout the experimental period, HUVECs bound Ulex europaeus lectin and expressed CD31, VE-cadherin, von Willebrand factor, as well as ICAM-2. A fraction of the cells also expressed the proliferation marker Ki67. Moreover, the sialomucin CD34, which is rapidly down-regulated in cultured HUVECs, was reinduced in vivo. However, we found no reinduction of CD34 in cells cultured inside or on top of Matrigel in vitro. We also injected cells suspended in Matrigel around the catheter tip of implanted osmotic pumps. Delivery of recombinant human interferon-gamma by this route led to strong induction of MHC class II and ICAM-1 on the human vessels. In conclusion, isolated human endothelial cells can integrate with the murine vascular system to form functional capillaries and regain in vivo properties.

Neisseria meningitidis lipopolysaccharides in human pathology

Neisseria meningitidis causes meningitis, fulminant septicemia or mild meningococcemia attacking mainly children and young adults. Lipopolysaccharides (LPS) consist of a symmetrical hexa-acyl lipid A and a short oligosaccharide chain and are classified in 11 immunotypes. Lipid A is the primary toxic component of N. meningitidis. LPS levels in plasma and cerebrospinal fluid as determined by Limulus amebocyte lysate (LAL) assay are quantitatively closely associated with inflammatory mediators, clinical symptoms, and outcome. Patients with persistent septic shock, multiple organ failure, and severe coagulopathy reveal extraordinarily high levels of LPS in plasma. The cytokine production is compartmentalized to either the circulation or to the subarachnoid space. Mortality related to shock increases from 0% to > 80% with a 10-fold increase of plasma LPS from 10 to 100 endotoxin units/ml. Hemorrhagic skin lesions and thrombosis are caused by up-regulation of tissue factor which induces coagulation, and by inhibition of fibrinolysis by plasminogen activator inhibitor 1 (PAI-1). Effective antibiotic treatment results in a rapid decline of plasma LPS (half-life 1-3 h) and cytokines, and reduced generation of thrombin, and PAI-1. Early antibiotic treatment is mandatory. Three intervention trials to block lipid A have not significantly reduced the mortality of meningococcal septicemia.

Fc alpha RI/CD89 circulates in human serum covalently linked to IgA in a polymeric state

The FcR for IgA CD89/FcalphaRI, is a type I receptor glycoprotein, expressed on myeloid cells, with important immune effector functions. In vitro CD89 can be released from CD89-expressing cells upon activation. Little information is available on the existence of this soluble molecule in vivo. Using specific and sensitive ELISA techniques (detection limit 50 pg/ml), we were not able to detect circulating CD89 in human sera. However, using Western blotting, a 30-kDa soluble CD89 molecule was demonstrated in both serum and plasma. Moreover, using a specific semiquantitative dot-blot system, we found CD89 in all human sera tested (mean concentration 1900 ng/ml). Size fractionation of human serum using gel filtration chromatography showed that the CD89 molecule was predominantly present in larger molecular mass fractions. Direct complexes between IgA and CD89 were demonstrated by anti-IgA affinity purification, and when analyzed under nonreducing conditions appeared to be covalently linked. Size fractionation of affinity-purified IgA showed the presence of soluble CD89 only in the high molecular mass fractions of IgA, but not in monomeric IgA. High molecular mass complexes of CD89-IgA could be distinguished from J chain containing dimeric IgA. These data show that CD89 circulates in complex with IgA, and suggest that CD89 might contribute to the formation of polymeric serum IgA.

CD89: the human myeloid IgA Fc receptor

CD89 (Fc alphaRI) is the human myeloid IgA Fc receptor expressed on cells, such as neutrophils, eosinophils and monocytes/macrophages. Cross-linking of CD89 on these cells, by IgA-opsonised particles (e.g. bacteria, viruses) or anti-CD89 monoclonal antibodies, can trigger various immunological effector functions which are generally protective but may also cause harm to the body. CD89 is a transmembrane glycoprotein that binds both subclasses of IgA in all its molecular forms (i.e. monomeric, dimeric and secretory IgA) via a region of its membrane-distal EC1 domain. DNA studies have shown that the CD89 gene is located within the newly described leukocyte receptor cluster (LRC) on chromosome 19. CD89 is more closely related to the KIR and MIR proteins, whose genes are also found in the LRC, than to other human Fc receptors (FcRs). On myeloid cells, CD89 is able to associate with the immunoreceptor tyrosine-based activation motif (ITAM)-containing the FcR gamma chain, which is responsible for intracellular signaling via CD89. Recently, it has been suggested that some cells express CD89 in a form that does not associate with the FcR gamma chain. Although the biological relevance of this observation is not yet clear, it may explain certain anti-inflammatory/inhibitory effects attributed to IgA. Here we review current knowledge concerning the genetics, structure and biological function of CD89.

Identification of residues within the extracellular domain 1 of bovine Fc gamma 2R essential for binding bovine IgG2

Neutrophils and monocytes in cattle express a novel class of immunoglobulin Fc receptor, specific for bovine IgG2 (bIgG2), termed bFc gamma 2R. In cows, the ability of neutrophils to kill immunoglobulin-opsonized microorganisms appears to depend largely on this subclass, whose interaction with bFc gamma 2R initiates the killing process. bFc gamma 2R is a transmembrane glycoprotein consisting of two extracellular immunoglobulin-like domains, followed by a 19-amino acid membrane-spanning region and a short cytoplasmic tail. Although related to other mammalian Fc gamma Rs, bFc gamma 2R belongs to a novel gene family that includes the human killer cell inhibitory receptor and Fc alpha RI (CD89) proteins. We have shown previously (Morton, H. C., van Zandbergen, G., van Kooten, C., Howard, C. J., van de Winkel, J. G., and Brandtzaeg, P. (1999) J. Exp. Med. 189, 1715-1722) that like these proteins (and unlike other Fc gamma Rs), bFc gamma 2R binds bIgG2 via the membrane-distal extracellular domain 1 (EC1). In this present study, we introduced mutations into the predicted loop regions of the EC1 domain and assayed the resulting bFc gamma 2R mutants for their ability to bind bIgG2. Our results indicated that the bIgG2 binding site lies within the predicted F-G loop region of the EC1 domain. Furthermore, single amino acid mutational analysis of this region identified Phe-82 and Trp-87 as being critical for bIgG2 binding.

Regulation of switching and production of IgA in human B cells in donors with duplicated alpha1 genes

IgA is the predominant immunoglobulin class synthesized in humans and can be subdivided into two subclasses, IgA1 and IgA2, each encoded by a separate gene and differentially expressed depending on age and anatomical localization of the producing cells. Duplication of the alpha1 gene is frequently observed in selected populations. As this duplication may serve to enhance IgA-mediated immunity, we determined its effect on switching and production of IgA in human B cells. We developed a nested PCR strategy, involving sequencing the switch (S) alpha2 region, the only human S region not sequenced to date, to assess the proportion of cells switching to IgA1 and IgA2 in vivo. Our results show that there is no difference in the serum and salivary levels of IgA1 and IgA or rate of switching to IgA1 and IgA between normal donors and individuals carrying alpha1 gene duplications, suggesting involvement of a regulatory step in the production of IgA.

A novel NF-kappa B/Rel site in intron 1 cooperates with proximal promoter elements to mediate TNF-alpha-induced transcription of the human polymeric Ig receptor

Secretory Abs constitute the first line of specific immune defense at mucosal surfaces. Such Abs are generated by the active transport of polymeric Ig (pIg) across secretory epithelia mediated by the pIgR, also known as transmembrane secretory component (SC). The proinflammatory cytokine TNF-alpha is a key mediator of host responses to infections, and it can stimulate protein synthesis-dependent transcriptional up-regulation of pIgR/SC in the HT-29 intestinal adenocarcinoma cell line. By reporter gene assay we identified a novel TNF-alpha-responsive region located within a 748-bp fragment in intron 1 of the human pIgR/SC gene which depended on an NF-kappaB/Rel site for full responsiveness. EMSAs demonstrated preferential binding of the NF-kappaB/Rel family member p65 (RelA) to this DNA element after TNF-alpha stimulation, with weaker and more delayed binding of p50. Furthermore, the TNF-alpha-responsive region in intron 1 required cooperation with DNA elements located in the proximal promoter region of the gene. Mutational analysis demonstrated that an IFN-stimulated response element near the transcriptional start site in exon 1 was involved in the TNF-alpha responsiveness. Thus, DNA elements located >4 kb apart were found to cooperate in TNF-alpha-induced pIgR/SC up-regulation. The intronic TNF-alpha-responsive enhancer overlapped with a recently identified IL-4-responsive enhancer. Several intronic DNA elements found to be functionally important in the human gene are highly conserved between the human and mouse pIgR/SC genes, suggesting the presence of a conserved cytokine-responsive enhancer region.

Age-related changes in CCR9+ circulating lymphocytes: are CCR9+ naive T cells recent thymic emigrants?

The chemokine receptor CCR9 is reported to be predominantly expressed by thymocytes as well as by circulating gut-homing and resident T cells in the small intestinal mucosa. Its ligand thymus-expressed chemokine (TECK) is produced by thymic and small intestinal epithelium. Here we report that the proportion of circulating CCR9+ naive T cells (mostly CD4+) declines with age, from approximately 15% of all T cells at birth to around 1% in adults. The proportion of CCR9+ T cells lacking the classical gut-homing receptor alpha4beta7, was much higher in children than in adults. Therefore, circulating CD3+CCR9+CD45RA+ cells have most likely left the thymus quite recently. This notion was supported by the small number of CCR9+ naive T cells which was present shortly after thymectomy. Establishing a phenotypic marker for recent thymic emigrants might provide a powerful tool in the clinical assessment and follow-up after cancer chemotherapy, hematopoietic stem cell transplantation, and during antiretroviral treatment of human immunodeficiency virus (HIV)-infected patients.

The J chain is essential for polymeric Ig receptor-mediated epithelial transport of IgA

Local production of secretory (S)IgA provides adaptive immunologic protection of mucosal surfaces, but SIgA is also protective when administered passively, such as in breast milk. Therefore, SIgA is a potential candidate for therapeutic administration, but its complex structure with four different polypeptide chains produced by two distinct cell types complicates recombinant production. The J chain is critical in the structure of SIgA because it is required for efficient polymerization of IgA and for the affinity of such polymers to the secretory component (SC)/polymeric (p)IgR. To better understand the role of the J chain in SIgA production, we have generated various mutant forms of the human J chain and analyzed the function of these mutants when coexpressed with IgA. We found that the C terminus of the J chain was not required for the formation of IgA polymers, but was essential for the binding of pIgA to SC. Likewise, we found that two of the intrachain disulfide bridges (Cys(13):Cys(101) and Cys(109):Cys(134)) were also required for the binding of pIgA to SC but, interestingly, not for IgA polymerization. Conversely, the last intrachain disulfide bridge (Cys(72):Cys(92)) was not essential for either of these two J chain functions. Finally, we demonstrated that the presence of only Cys(15) or Cys(69) was sufficient to support polymerization of IgA, but that these polymers were mostly noncovalently stabilized. Nevertheless, these polymers bound free SC with nearly the same affinity as pIgA containing wild-type J chain, but were transcytosed by pIgR-expressing polarized epithelial cells at a reduced efficiency.

Cellular activating properties and morphology of membrane-bound and purified meningococcal lipopolysaccharide

Neisseria meningitidis, the cause of epidemic meningitis and acute lethal sepsis, synthesizes surplus lipopolysaccharides (LPSs) during growth, which are released as outer membrane vesicles (OMV) or "blebs". Meningococcal disease severity is related to plasma LPS levels. We have compared the biological activities of native outer membrane vesicles (nOMV) to those of purified Nm-LPS (Nm-LPS) and LPS-depleted OMV (dOMV) prepared from N. meningitidis. The LPS content of nOMV was determined spectrophotometrically by quantifying KDO and by silver-stained SDS-PAGE gels. The morphology of the preparations was studied by transmission electron microscopy. The Limulus amoebocyte lysate (LAL) assay was used to quantify LPS in the plasma solutions. The preparations were diluted in endotoxin-free heparin plasma to equal amounts of LPS (w/w) in the range 50-5000 pg/ml. The biological reactivity was tested by: (i) a monocyte target-assay (monocyte purity > or =96%); and (ii) a whole blood model, measuring the secretion of TNF-alpha and IL-6 induction of procoagulant activity in monocytes (PCA). In both models, nOMV induced dose-dependent cell responses (TNF-alpha, IL-6, PCA) similar to purified Nm-LPS, whereas dOMV induced minimal responses. However, LAL activity was significantly higher for nOMV than for purified Nm-LPS and dOMV. The cellular responses of purified Nm-LPS and nOMV were reduced (>95%) by a specific anti-CD14-antibody.

Cloning and sequencing of a cDNA encoding the bovine FcR gamma chain

Phagocytic cells of the immune system express specific receptors for the Fc region of immunoglobulins (FcRs). In humans, most FcRs for IgG (FcgammaR), IgA (FcalphaR) and IgE (FcvarepsilonR) consist of an immunoglobulin (Ig) -binding subunit associated with a specialized signaling molecule, the FcR gamma chain. The FcR gamma chain is crucial for the transmission of intracellular signals following receptor ligation. In cattle, however, although four distinct complimentary DNAs (cDNAs) encoding IgG-binding subunits have been described (corresponding to bovine FcgammaRI, FcgammaRII, FcgammaRIII, and Fcgamma2R), virtually, nothing is known about signal transduction via bovine FcRs. Therefore, in this study, a cDNA encoding the bovine FcR gamma chain was cloned. The cDNA is 258 base pairs long and encodes a protein of 85 amino-acids. The mature protein shows high homology with the FcR gamma chains from several other species. Interestingly, the cytoplasmic domain of the bovine FcR gamma chain is one amino-acid shorter than those previously described. Cloning of a cDNA encoding, the bovine FcR gamma chain will allow for a better understanding of signal transduction processes triggered by bovine FcRs.

Nature and function of gastrointestinal antigen-presenting cells

Antigen-presenting cells (APCs) of the human gut are heterogeneous, including both macrophages, a variety of dendritic cells and B cells. They are found both in gut-associated lymphoid tissue and in the mucosal lamina propria, especially beneath the surface epithelium. APCs have diverse phenotypes and therefore probably different functions in various locations; their expression levels of a variety of costimulatory molecules are most likely important for immunological decision making of stimulated T cells, either locally in the gut or in regional lymph nodes to which migrating APCs (dendritic cells) carry antigen. Thus, APCs are involved in active immunity as well as in induction of oral tolerance. However, their precise role in food allergy remains to be defined.

Inflammatory bowel disease: clinics and pathology. Do inflammatory bowel disease and periodontal disease have similar immunopathogeneses?

Inflammatory bowel disease (IBD) comprises two chronic, tissue-destructive, clinical entities Crohn disease (CD) and ulcerative colitis (UC) both apparently caused by immunological overreaction (hypersensitivity) to commensal gut bacteria. Under normal conditions the intestinal immune system shows a down-regulating tone ('oral tolerance') against dietary antigens and the indigenous microbiota. This local homeostasis is disturbed in IBD, leading to hyperactivation of T helper 1 (Th1) cells with abundant secretion of interferon-gamma and tumor necrosis factor (TNF) and production of IgG antibodies against commensal bacteria. In addition, UC includes genetically determined autoimmunity, particularly IgG1-mediated cytotoxic epithelial attack. Breaching of the epithelium is the best-defined event underlying abrogation of oral tolerance, but immune deviation caused by cytokines fiom irritated epithelial cells or subepithelial elements (for example, mast cells, natural killer cells, macrophages) may also be involved. Endogenous infection with local hypersensitivity likewise causes periodontal disease, reflecting 'frustrated' immune elimination mechanisms entertained by antigens from dental plaque. Altogether, perturbation of a tightly controlled cytokine network, with abnormal crosstalk between several cell types, apparently explains the progressive immunopathology of chronic inflammatory mucosal diseases in general. This adverse development will be influenced by numerous immunity genes, the dosage and potential pathogeniciy of commensal bacteria, general health, nutritional status, and psychological factors. Several targets for new therapy have tentatively been identified to block immunopathological mechanisms in IBD, and inhibition of TNF has a striking beneficial effect in CD, supporting a central role of this cytokine.

Plasmacytoid dendritic cells (natural interferon- alpha/beta-producing cells) accumulate in cutaneous lupus erythematosus lesions

Plasmacytoid dendritic cell (P-DC) precursors in peripheral blood produce large amounts of interferon (IFN)-alpha/beta when triggered by viruses. However, when incubated with interleukin-3 and CD40 ligand, the same precursors differentiate into mature DCs that stimulate naïve CD4(+) T cells to produce Th2 cytokines. We recently reported that P-DCs accumulate in nasal mucosa of experimentally induced allergic rhinitis, supporting a role for this DC subset in Th2-dominated inflammation. Here we examined whether P-DCs accumulate in cutaneous lesions of lupus erythematosus (LE), a disorder associated with increased IFN-alpha/beta production. Our results showed that P-DCs were present in 14 out of 15 tissue specimens of cutaneous LE lesions, but not in normal skin. Importantly, the density of P-DCs in affected skin correlated well (r(s) = 0.79,P < 0.0005) with the high number of cells expressing the IFN-alpha/beta-inducible protein MxA, suggesting that P-DCs produce IFN-alpha/beta locally. Accumulation of P-DCs coincided also with the expression of L-selectin ligand peripheral lymph node addressin on dermal vascular endothelium, adding further support to the notion that these adhesion molecules are important in P-DC extravasation to peripheral tissue sites. Together, our findings suggested that P-DCs are an important source of IFN-alpha/beta in cutaneous LE lesions and may therefore be of pathogenic importance.