Potential role of superantigen induced activation of cell mediated immune mechanisms in the pathogenesis of Crohn's disease

Mouse mammary tumor virus is implicated in severity of colitis and dysbiosis in the IL-10-/- mouse model of inflammatory bowel disease

BACKGROUND

Following viral infection, genetically manipulated mice lacking immunoregulatory function may develop colitis and dysbiosis in a strain-specific fashion that serves as a model for inflammatory bowel disease (IBD). We found that one such model of spontaneous colitis, the interleukin (IL)-10 knockout (IL-10-/-) model derived from the SvEv mouse, had evidence of increased Mouse mammary tumor virus (MMTV) viral RNA expression compared to the SvEv wild type. MMTV is endemic in several mouse strains as an endogenously encoded Betaretrovirus that is passaged as an exogenous agent in breast milk. As MMTV requires a viral superantigen to replicate in the gut-associated lymphoid tissue prior to the development of systemic infection, we evaluated whether MMTV may contribute to the development of colitis in the IL-10-/- model.

RESULTS

Viral preparations extracted from IL-10-/- weanling stomachs revealed augmented MMTV load compared to the SvEv wild type. Illumina sequencing of the viral genome revealed that the two largest contigs shared 96.4-97.3% identity with the mtv-1 endogenous loci and the MMTV(HeJ) exogenous virus from the C3H mouse. The MMTV sag gene cloned from IL-10-/- spleen encoded the MTV-9 superantigen that preferentially activates T-cell receptor Vβ-12 subsets, which were expanded in the IL-10-/- versus the SvEv colon. Evidence of MMTV cellular immune responses to MMTV Gag peptides was observed in the IL-10-/- splenocytes with amplified interferon-γ production versus the SvEv wild type. To address the hypothesis that MMTV may contribute to colitis, we used HIV reverse transcriptase inhibitors, tenofovir and emtricitabine, and the HIV protease inhibitor, lopinavir boosted with ritonavir, for 12-week treatment versus placebo. The combination antiretroviral therapy with known activity against MMTV was associated with reduced colonic MMTV RNA and improved histological score in IL-10-/- mice, as well as diminished secretion of pro-inflammatory cytokines and modulation of the microbiome associated with colitis.

CONCLUSIONS

This study suggests that immunogenetically manipulated mice with deletion of IL-10 may have reduced capacity to contain MMTV infection in a mouse-strain-specific manner, and the antiviral inflammatory responses may contribute to the complexity of IBD with the development of colitis and dysbiosis. Video Abstract.

The systemic and pulmonary immune response to staphylococcal enterotoxins

In response to environmental cues the human pathogen Staphylococcus aureus synthesizes and releases proteinaceous enterotoxins. These enterotoxins are natural etiologic entities of severe food poisoning, toxic shock syndrome, and acute diseases. Staphylococcal enterotoxins are currently listed as Category B Bioterrorism Agents by the Center for Disease Control and Prevention. They are associated with respiratory illnesses, and may contribute to exacerbation of pulmonary disease. This likely stems from the ability of Staphylococcal enterotoxins to elicit powerful episodes of T cell stimulation resulting in release of pro-inflammatory cytokines. Here, we discuss the role of the immune system and potential mechanisms of disease initiation and progression.

Regulatory T cells modulate staphylococcal enterotoxin B-induced effector T-cell activation and acceleration of colitis

Oral administration of bacterial superantigen Staphylococcus aureus enterotoxin B (SEB) activates mucosal T cells but does not cause mucosal inflammation. We examined the effect of oral SEB on the development of mucosal inflammation in mice in the absence of regulatory T (Treg) cells. SCID mice were fed SEB 3 and 7 days after reconstitution with CD4(+) CD45RB(high) or CD4(+) CD45RB(high) plus CD4(+) CD45RB(low) T cells. Mice were sacrificed at different time points to examine changes in tissue damage and in T-cell phenotypes. Feeding SEB failed to produce any clinical effect on SCID mice reconstituted with CD4(+) CD45RB(high) and CD4(+) CD45RB(low) T cells, but feeding SEB accelerated the development of colitis in SCID mice reconstituted with CD4(+) CD45RB(high) T cells alone. The latter was associated with an increase in the number of CD4(+) Vbeta8(+) T cells expressing CD69 and a significantly lower number of CD4(+) CD25(+) Foxp3(+) T cells. These changes were not observed in SCID mice reconstituted with both CD45RB(high) and CD45RB(low) T cells. In addition, SEB impaired the development of Treg cells in the SCID mice reconstituted with CD4(+) CD45RB(high) T cells alone but had no direct effect on Treg cells. In the absence of Treg cells, feeding SEB induced activation of mucosal T cells and accelerated the development of colitis. This suggests that Treg cells prevent SEB-induced mucosal inflammation through modulation of SEB-induced T-cell activation.

IFN-gamma expression in CD8+ T cells regulated by IL-6 signal is involved in superantigen-mediated CD4+ T cell death

Infection with pathogens containing superantigens (Sags) can result in massive excessive CD4+ T cell activation and death in such conditions as toxic shock, food poisoning and autoimmune diseases. We here showed how enhancement of IL-6 signaling suppresses Sag-mediated activated CD4+ T cell death. Sag-induced CD4+ T cell death increased in IL-6 knockout (KO) mice, whereas it decreased in mice characterized by enhanced IL-6-gp130-STAT3 signaling. The serum concentration of IFN-gamma was inversely correlated with the magnitude of IL-6 signaling, and IFN-gamma deficiency inhibited Sag-induced activated CD4+ T cell death, suggesting that IL-6 suppresses CD4+ T cell death via IFN-gamma expression. Interestingly, depletion of activated CD8+ T cells inhibited Sag-mediated increases in IFN-gamma expression in IL-6 KO mice as well as the augmented CD4+ T cell death. The results demonstrate that IL-6-gp130-STAT3 signaling in activated CD8+ T cells contributes to Sag-induced CD4+ T cell death via IFN-gamma expression, highlighting this signaling axis in CD8+ T cells as a potential therapeutic target for Sag-related syndromes.

Rhinosinusitis derived Staphylococcal enterotoxin B possibly associates with pathogenesis of ulcerative colitis

Background

During clinical practice, we noticed that some patients with both ulcerative colitis (UC) and chronic rhinosinusitis (CRS) showed amelioration of UC after treatment of CRS. This study was designed to identify a possible association between CRS and UC.

Methods

Thirty-two patients with both CRS and UC received treatment with functional endoscopic sinus surgery (FESS) for CRS. Clinical symptom scores for CRS and UC, as well as serum levels of anti-Staphylococcal enterotoxin B (SEB) were evaluated at week 0 and week 12. Sinus wash fluid SEB content was measured with enzyme-linked immunosorbent assay (ELISA). The surgically removed tissues were cultured to identify growth of Staphylococcus. aureus (S. aureus). Immunohistochemistry was employed to identify anti-SEB positive cells in the colonic mucosa. Colonic biopsies were obtained and incubated with SEB. Mast cell activation in the colonic mucosa in response to incubation with SEB was observed with electron microscopy and immunoassay.

Results

The clinical symptom scores of CRS and UC severe scores (UCSS) were significantly reduced in the UC-CRS patients after FESS. The number of cultured S. aureus colonies from the surgically removed sinus mucosa significantly correlated with the decrease in UCSS. High levels of SEB were detected in the sinus wash fluids of the patients with UC-CRS. Histamine and tryptase release was significantly higher in the culture supernate in the patients with UC-CRS than the patients with UC-only and normal controls. Anti-SEB positive cells were located in the colonic mucosa.

Conclusion

The pathogenesis of UC in some patients may be associated with their pre-existing CRS by a mechanism of swallowing sinusitis-derived SEB. We speculate that SEB initiates inappropriate immune reactions and inflammation in the colonic mucosa that further progresses to UC.

A murine model of ulcerative colitis: induced with sinusitis-derived superantigen and food allergen

BACKGROUND

The etiology of ulcerative colitis (UC) is to be understood. The basic pathological feature of UC is intestinal chronic inflammation. Superantigen, such as Staphylococcus enterotoxin B (SEB), is reported to compromise intestinal barrier function by increasing epithelial permeability and initiate inflammation in the intestinal mucosa. Inasmuch as anatomic position of the sinus, chronic sinusitis-derived SEB may follow the secretion and to be swallowed down to the gastrointestinal tract and induce lesions to the intestinal mucosa.

METHODS

Sinus wash fluid (SWF, containing SEB) was collected from a group of patients with both chronic sinusitis (CS) and UC. A group of mice were sensitized to ovalbumin (OVA) in the presence of SWF. The sensitized mice were challenged with the specific antigen OVA. The inflammatory status of the colonic tissue was determined with histology, serology and electron microscopy. Using horseradish peroxidase (HRP) as a tracer, another group of mice was stimulated with SWF for 2 hours. The HRP activity was detected in the colonic tissue with enzymatic approaches and electron microscopy.

RESULTS

Epithelial hyperpermeability in colonic epithelium was induced by stimulating with SWF. The HRP activity in the colonic mucosa was almost 11 times more in the SWF treated group (3.2 +/- 0.6 microg/g tissue) than the control group (0.3 +/- 0.1 microg/g tissue). Mice were sensitized using a mixture of SWF and OVA (serum OVA-specific IgE was detected with a highest titer as 1:64). Challenge with OVA induced extensive inflammation in the colonic mucosa by showing (1) marked degranulation in mast cells (MC, 46.3 +/- 4.5%) and eosinophils (Eo, 55.7 +/- 4.2%); (2) inflammatory cell infiltration (MC = 145.2 +/- 11.4; Eo = 215.8 +/- 12.5; mononuclear cell = 258.4 +/- 15.3/mm2 tissue); (3) increased MPO activity (12.9 +/- 3.2 U/g tissue) and inflammatory scores (1.8 +/- 0.3); (4) mucosal surface ulcers; (5) edema in the lamina propria; (6) bacterial translocation and abscess formation in the subepithelial region.

CONCLUSION

Introducing Sinusitis-derived SEB-containing SWF to the gastrointestinal tract compromised colonic mucosal barrier function increasing epithelial permeability to luminal macromolecular protein in mice. The SWF facilitated colonic mucosal sensitization to luminal antigen. Multiple challenging the sensitized colonic mucosa with specific antigen OVA induced inflammation, induced a condition similar to human ulcerative colitis.

Oral Administration of the Bacterial Superantigen Staphylococcal Enterotoxin B Induces Activation and Cytokine Production by T Cells in Murine Gut-Associated Lymphoid Tissue

The toxicity of the staphylococcal enterotoxins (SEs) has been linked to the activation of large numbers of T cells in the peripheral lymphoid tissues. Because the primary manifestations of foodborne enterotoxic poisoning are associated with the gastrointestinal tract, we have compared the responses of T cells in the gut-associated lymphoid tissue and in the periphery to intragastric (i.g.) and i.p. administration of SEB. Intraperitoneal SEB results in an early expansion of peripheral Vβ8+ T cells and Th1 cytokine secretion followed by deletion at 7–10 days. We found that i.g. SEB rapidly (within 4 h) leads to the expansion and activation of Vβ8+ T cells in the Peyer’s patch and mesenteric lymph nodes. Analysis of cytokine mRNA in purified Vβ8+ T cells by competitive RT-PCR showed that, 4 h after i.g. SEB, the induction of mRNA for IL-2 and IFN-γ is about 10-fold greater in mucosal than in peripheral lymphoid tissue. Our results show that activated mucosal T cells expand and up-regulate cytokine mRNA in response to luminal exposure to SEB, suggesting a role for the gut-associated lymphoid tissue in the gastrointestinal manifestations of enterotoxic poisoning.

Changes in murine jejunal morphology evoked by the bacterial superantigen Staphylococcus aureus enterotoxin B are mediated by CD4+ T cells

Bacterial superantigens (SAgs) are potent T-cell stimuli that have been implicated in the pathophysiology of autoimmune and inflammatory disease. We used Staphylococcus aureus enterotoxin B (SEB) as a model SAg to assess the effects of SAg exposure on gut form and cellularity. BALB/c, SCID (lacking T cells) and T-cell-reconstituted SCID mice were treated with SEB (5 or 100 microg intraperitoneally), and segments of the mid-jejunum were removed 4, 12, or 48 h later and processed for histochemical or immunocytochemical analysis of gut morphology and major histocompatibility complex class II (MHC II) expression and the enumeration of CD3+ T cells and goblet cells. Control mice received saline only. SEB treatment of BALB/c mice caused a time- and dose-dependent enteropathy that was characterized by reduced villus height, increased crypt depth, and a significant increase in MHC II expression. An increase in the number of CD3+ T cells was observed 48 h after exposure to 100 microg of SEB. Enteric structural alterations were not apparent in SEB-treated SCID mice compared to saline-treated SCID mice. In contrast, SEB challenge of SCID mice reconstituted with a mixed lymphocyte population or purified murine CD4+ T cells resulted in enteric histopathological changes reminiscent of those observed in SEB-treated BALB/c mice. These findings implicate CD4+ T cells in this SEB-induced enteropathy. Our results show that SAg immune activation causes significant changes in jejunal villus-crypt architecture and cellularity that are likely to impact on normal physiological processes. We speculate that the elevated MHC II expression and increased number of T cells could allow for enhanced immune responsiveness to other SAgs or environmental antigens.

Streptococcal pyrogenic exotoxin A (SPE A) superantigen induced production of hematopoietic cytokines, IL-12 and IL-13 by human peripheral blood mononuclear cells

A quantitative and kinetic study of the release of the hematopoietic cytokines IL-3, IL-5 and GM-CSF, the immunoregulatory cytokine IL-12 heterodimer (and its p40 subunit) and IL-13 by human peripheral blood mononuclear cells (PBMC) stimulated in vitro with the superantigen streptococcal pyrogenic (erythrogenic) exotoxin A (SPE A) from Streptococcus pyogenes is reported. PBMC were stimulated in parallel with heat-killed group A streptococcal cells, E. coli lipopolysaccharide (LPS) and with concanavalin A (Con A) in certain experiments for comparative purposes. The cytokines were assayed in the supernatant fluids by ELISA. IL-13 expression was also determined by a quantitative competitive PCR. IL-3, IL-5, GM-CSF, IL-12 p40, IL-12 heterodimer and IL-13 expression was induced by SPE A in a time- and dose-dependent manner in rather substantial amounts except the IL-12 heterodimer, which was released in small quantities. In contrast to SPE A, IL-3, IL-5 and IL-13 were not or poorly elicited by streptococcal cells or LPS whereas these two stimulants induced relatively high amounts of GM-CSF. Interestingly, both IL-12 p40 and IL-12 heterodimer were released in much higher amounts by streptococcal cells. Con A induced IL-3, IL-5, GM-CSF and IL-13 production in amounts comparable to those elicited by SPE A. The possible pathophysiological relevance of the elicitation by SPE A and streptococcal cells of these cytokines is discussed.

HLA class II gene frequencies in Crohn's disease: a population based analysis in Germany

BACKGROUND

Ulcerative colitis is the only known inflammatory bowel disease associated with particular HLA alleles. Whereas the association with the HLA-DRB1*15 allele has been described in several independent studies for ulcerative colitis, no contribution of HLA alleles to susceptibility in Crohn's disease has yet been shown.

AIM

This study was designed to study the strength of association of HLA class II alleles as risk markers for Crohn's disease in a homogenous population in Germany.

PATIENTS

A total of 4251 randomly selected control subjects, and 162 unrelated subjects with Crohn's disease were studied. Subjects were studied for their HLA-DRB1, HLA-DQA1, and HLA-DQB1 alleles.

METHOD

HLA DNA typing was performed after locus specific amplification with the polymerase chain reaction and reverse dot blot hybridisation.

RESULTS

The HLA-DRB1*07 was the only HLA class II allele found to be significantly associated with Crohn's disease (relative risk (RR) = 1.9, 95% CI: 1.66 to 2.14; p = 0.0001). This association remained significant after correction for the number of DRB1 alleles compared. In patients with disease onset before 35 years the RR for the disease in HLA-DRB1*07 positive subjects was found to be higher (RR = 3.1, 95% CI: 2.44 to 3.76). The HLA-DRB1*03 was significantly decreased in frequency in Crohn's disease (RR = 0.5, 95% CI: 0.39 to 0.61; p = 0.0028).

CONCLUSION

The HLA-DRB1*07 allele provides risk for the disease especially in patients with younger ages of onset. These data also provide indirect evidence for an immunogenetically based heterogeneity of the disease.