Intolerance of the dirty intestine

The link between COPD and ankylosing spondylitis: A population based study

BACKGROUND

Ankylosing spondylitis (AS) is one of the most common and severe subtypes of the spondyloarthropathies. Extra-articular involvement among AS patients, including lung disease, has been described widely. Chronic obstructive pulmonary disease (COPD) has been linked to several autoimmune diseases, however, very few studies have investigated the association between AS and COPD.

OBJECTIVE

To assess whether an association exists between AS and COPD.

MATERIAL AND METHODS

A population-based cross-sectional study was conducted using data retrieved from the largest electronic medical records database in Israel, the Clalit Health Services (CHS). Patients were defined as having AS or COPD when there was at least one such documented diagnosis in their medical records. The proportion of COPD was compared between AS patients and controls. A logistic regression model was used to estimate the association between AS and COPD in a multivariate analysis adjusted for age, gender and smoking status.

RESULTS

The study included 4076 patients with AS and 20,290 age- and sex-frequency matched controls. The proportion of COPD in AS patients was higher than in controls (46% vs. 18%, respectively, p < .001). Multivariate logistic regression demonstrated a robust independent association between AS and COPD (OR 1.225, p = .031).

CONCLUSION

Our study supports an association between AS and COPD, further extending the link between COPD and autoimmune diseases. This finding highlights the importance of smoking cessation in AS patients and raises the question of whether COPD screening may be warranted.

Enhanced oral tolerance in transgenic mice with hepatocyte secretion of IL-10

Several cytokines derived from Th3 and Tr1 cells, including IL-10, are believed to regulate oral tolerance, but direct evidence is lacking. We have explored the potential role of IL-10 by generating transgenic (TG) mice with sustained hepatocyte-specific expression of rat IL-10. TG mice expressed rat IL-10 downstream of a transthyretin promoter, which led to serum levels that were increased 10- to 100-fold compared with normal animals. Animals were orally administered 1 mg of whole OVA for 5 consecutive days, with control animals receiving PBS. There were six animal groups: Either OVA or PBS were fed orally to rat IL-10 TG mice, non-TG wild-type mice without IL-10 administration, and non-TG wild-type mice administered rat IL-10 systemically. On day 8, all mice were immunized with two injections of OVA, and then analyzed on day 18. T cell proliferation responses were reduced by 65.8 +/- 14.3% after feeding of OVA in rIL-10 TG animals, compared with 39.4 +/- 15.6% in the non-TG mice (p = 0.02). Anti-OVA titers were expressed as fold increase over naive non-TG mice. After feeding, titers decreased by approximately 33% (from 3- to 2-fold) in TG animals and, to a lesser extent, in non-TG animals. IFN-gamma secretion by cultured popliteal lymphocytes decreased in TG animals by 83% after feeding and by 69% in non-TG animals. IL-4 secretion increased 4-fold in TG-fed mice, but did not significantly change in non-TG OVA-fed animals. In contrast to hepatic TG expression of rIL-10, systemic administration of rIL-10 had only a modest effect on tolerance. IL-10, when transgenically expressed in the liver enhances mucosal tolerance to an oral Ag.

The macrophage F4/80 receptor is required for the induction of antigen-specific efferent regulatory T cells in peripheral tolerance

We show that the mouse macrophage-restricted F4/80 protein is not required for the development and distribution of tissue macrophages but is involved in the generation of antigen-specific efferent regulatory T (T reg) cells that suppress antigen-specific immunity. In the in vivo anterior chamber (a.c.)–associated immune deviation (ACAID) model of peripheral tolerance, a.c. inoculation of antigen into F4/80^−/− mice was unable to induce efferent T reg cells and suppress delayed-type hypersensitivity (DTH) responses. Moreover, the use of anti-F4/80 mAb and F4/80^−/− APCs in an in vitro ACAID model showed that all APC cells in the culture must be able to express F4/80 protein if efferent T reg cells were to be generated. In a low-dose oral tolerance model, WT but not F4/80^−/− mice generated an efferent CD8⁺ T reg cell population that suppressed an antigen-specific DTH response. Peripheral tolerance was restored in F4/80^−/− mice by adoptive transfer of F4/80⁺ APCs in both peripheral tolerance models, indicating a central role for the F4/80 molecule in the generation of efferent CD8⁺ T reg cells.

Mechanisms of natural tolerance in the intestine: implications for inflammatory bowel disease

Tolerance, the regulated inability to respond to a specific immunologic stimulant, is a physiological event important to normal immune function. Just as loss of tolerance to self-proteins results in autoimmune diseases, we assert that loss of tolerance to commensal flora in the intestinal lumen leads to inflammatory bowel disease (IBD). Mechanisms through which the mucosal immune system establishes and remains hyporesponsive toward the presence of food proteins and commensal flora, which we define as natural tolerance, are discussed. In addition to the contributions by commensal flora, the innate host defense and the adaptive immune systems promote natural tolerance to sustain normal mucosal homeostasis. Understanding the molecular and cellular events that mediate natural tolerance will lead to more advanced insights into IBD pathogenesis and improved therapeutic options.

Oral tolerance

The ability of the mucosal immune system to distinguish between harmful and harmless antigens is essential for mounting protective immune responses and preventing the induction of mucosal pathology yet the basis for this remains unclear. As fed antigen can also exert systemic effects understanding oral tolerance and priming will also have important consequences for therapy and vaccination. Here we will not only review the increasing amount of information about the potential mechanisms of oral tolerance and priming but also attempt to shed some light on how differences in the uptake and handling i.e. 'the journey' of orally administered antigen may promote these mechanisms.

Oral tolerance

The intestinal immune system discriminates between potentially harmful and harmless foreign proteins. The basis for this differential response may be related to the conditions of antigen presentation by antigen-presenting cells, as determined by their phenotype or activation state. How these conditions affect specific immunologic unresponsiveness to later challenge with an antigen is not known. Two possible mechanisms are the induction of anergy or deletion of responsive cells and the activation of regulatory cells or mediators, and the mechanism may very depending on the tolerizing regimen used. Should regulatory cells be involved, they are speculated to induce tolerance through their production of inhibitory cytokines, such as IL-4, IL-10, and TGF-beta. Studies using specific antibodies and selective genetic knockout (KO) strains of mice, however, have provided conflicting data. A final intriguing possibility is that tolerance results from cognate interactions between T cells and APCs, so that tolerant T cells or APCs prime T cells they contact to deliver a tolerogenic signal to the next T cell they encounter, possibly through a function dependent on interactions between Notch family receptors and their ligands. As with many questions in mucosal immunology, definition of the mechanisms of oral tolerance (OT) has proved difficult to address experimentally, but promising approaches include study of the distribution of fed antigen, of targeted genetic KOs, and of transgenic strains.

Basic mechanisms and clinical implications of oral tolerance

Oral tolerance is the physiologic mechanism that prevents hypersensitivity to food proteins and probably to commensal bacteria. It has also attracted attention as a means of administering therapy for autoimmune and inflammatory diseases. Although evidence indicates that both clonal inactivation and active regulatory mechanisms may play a role and that the induction of these may be determined selectively by the feeding regimen used to induce tolerance, the exact mechanisms of oral tolerance remain unclear. Here, we discuss recent evidence that fed antigens are presented to CD4(+) T cells by antigen-presenting cells (APCs) that lack costimulatory activity, resulting in partial activation of T cells followed by a state of unresponsiveness. This seems to occur in many tissues of the immune system but may be particularly important in the draining mesenteric lymph node. Resting dendritic cells may be the predominant population of APCs involved in oral tolerance, and conditions that activate dendritic cells allow the induction of productive immunity. Conventionally, presentation of antigen in the absence of costimulation is thought to induce T-cell anergy, but evidence now indicates that anergic T cells can also act as regulatory cells via the production of inhibitory mediators or via cognate interactions with APCs and other T cells. We discuss how an ability to deactivate APCs may explain bystander suppressor activity in oral tolerance, and we consider how the production of transforming growth factor-beta or interleukin-10 by Th3 or T regulatory 1 cells may contribute to tolerance in vivo. We speculate that both the production of inhibitory mediators and the delivery of suppression via cognate interactions may be properties of otherwise "anergic" T cells.