On the etiology of Crohn disease

Elevated antibody responses in patients with Crohn's disease against a 14-kDa secreted protein purified from Mycobacterium avium subsp. paratuberculosis

Patients with Crohn's disease (CD) (n = 10) and ulcerative colitis (UC) (n = 10) were tested for immune responses against various antigens from Mycobacterium avium subsp. paratuberculosis; alkyl hydroperoxide reductase C (AhpC) and alkyl hydroperoxide reductase D (AhpD), which are constitutively expressed in this species as opposed to other mycobacteria, a 14-kDa secreted antigen and PPD-J. The CD patients had significantly elevated antibody levels against the 14 kDa protein (P < 0.05) that were negatively correlated with the duration of the disease (r(s) = - 0.85). They also seemed to have increased antibody levels against AhpC and AhpD, but the differences between the two groups were not significant. However, taken together, the antibody responses to three individual mycobacterial antigens in CD patients strengthen the possibility that the observed responses are caused by mycobacterial infection. No significant differences in the interferon (IFN)-gamma production, the interleukin (IL)-10 production and the ability to proliferate upon stimulation with these antigens were observed. These results show that measuring antibody responses against purified specific antigens is a suitable and simple approach when assessing the connection between CD and mycobacteria in patients with clinical CD. Another important aspect in such studies is to have well defined patient groups tested at the onset of clinical symptoms.

Results of multiple diagnostic tests for Mycobacterium avium subsp. paratuberculosis in patients with inflammatory bowel disease and in controls

Mycobacterium avium subsp. paratuberculosis has been incriminated as a cause of Crohn's disease (CD); however, studies to date have been relatively small and generally only used a single diagnostic assay. The objective of the study was to reexamine the association of M. avium subsp. paratuberculosis and CD using multiple diagnostic tests. Five methods were used to detect M. avium subsp. paratuberculosis infections in 439 inflammatory bowel disease (IBD) patients and 324 control subjects in the United States and Denmark. Most assays were adaptations of diagnostic tests for this infection performed routinely on animals. PCR for IS900, a genetic element unique to M. avium subsp. paratuberculosis, was positive significantly more often on resected bowel and lymph node tissues from CD patients (19.0%) and ulcerative colitis (UC) patients (26.2%) than from controls (6. 3%) (P < 0.05). Positive IS900 PCR results occurred more often in U. S. than in Danish IBD patients, 32.0 versus 13.3% (P = 0.025). The majority of Danish patients were bacillus Calmette-Guérin (Mycobacterium bovis BCG) vaccinated (CD, 77.5%; UC, 86.6%; controls, 83.0%) whereas none of the U.S. patients with IBD and only 2% of U. S. controls were vaccinated. Among Danish IBD patients, positive PCR findings were four times more common among subjects who were not BCG vaccinated (33.3%) than among BCG vaccinates (8.8%, P = 0.02). Culture of the same tissues tested by PCR using modified BACTEC 12B medium failed to grow M. avium subsp. paratuberculosis from patients or controls. U.S. CD patients had the highest serological evidence (enzyme-linked immunosorbent assay [ELISA] for serum antibodies) of M. avium subsp. paratuberculosis infection (20.7% of patients positive) which was higher than for all UC patients studied (6.1%) or healthy controls (3.8%, P < 0.005). Among Danish patients alone, however, no significant differences in rates of ELISA-positive results among CD, UC, or control patients were found. For 181 study subjects, both IS900 PCR and ELISA were performed. Although 11 were ELISA positive and 36 were PCR positive, in no instance was a patient positive by both tests, suggesting that these states are mutually exclusive. Evaluation of cytokine-mediated immune responses of IBD patients was complicated by the influence of immunosuppressive therapy given most IBD patients. Gamma interferon (IFN-gamma) release by peripheral blood leukocytes after M. avium purified protein derivative PPD antigen stimulation showed significantly lower responses in CD patients than in UC patients or controls in both U.S. (by ex vivo assay) and Danish (by in vitro assay) populations (P < 0.05). Interleukin-5 responses were not different among CD, UC, or control groups. Collectively, the PCR, ELISA, and IFN-gamma tests for M. avium subsp. paratuberculosis together with the unexpected observation that BCG vaccination influenced M. avium subsp. paratuberculosis detection, lead us to conclude that M. avium subsp. paratuberculosis, or some similarly fastidious mycobacterial species, infects at least a subset of IBD patients. Whether the infection is primary (causal) or secondary, it may contribute to the etiopathogenesis of IBD.

Identification of a novel bacterial sequence associated with Crohn's disease

BACKGROUND & AIMS

Enteric microorganisms are implicated in the pathogenesis of Crohn's disease (CD), but no clear bacterial or viral species has been identified. In this study, representational difference analysis (RDA) was used to isolate DNA segments preferentially abundant in lamina propria mononuclear cells of lesional mucosa vs. adjacent uninvolved mucosa.

METHODS

Two RDA-derived microbial sequences were isolated (I1 and I2) and identified as novel homologues of the ptxR and tetR bacterial transcription-factor families.

RESULTS

Quantitative competitive polymerase chain reaction of paraffin-embedded intestinal specimens from 212 patients showed that I2 DNA was present in many CD colonic lesions (43%), but was infrequent in other colonic specimens (9% of ulcerative colitis lesions and 5% of non-inflammatory bowel disease diseases; P<0.0001). I2 was prevalent in ileal specimens, regardless of disease status (43%-54%). Enzyme-linked immunosorbent assay analysis of 150 individuals with an I2 glutathione-S-transferase fusion protein showed frequent immunoglobulin A seroreactivity in CD (54% of patients), but infrequent seroreactivity in patients with ulcerative colitis, other inflammatory enteric diseases, or normals (10%, 19%, and 4%, respectively; P<0.001 to 0.00001).

CONCLUSIONS

These findings relate CD to a novel lesion-localized and immunologically associated bacterial sequence, suggesting that the microorganism expressing the I2 gene product may be related to CD pathogenesis.

Effect of three factors in cheese production (pH, salt, and heat) on Mycobacterium avium subsp. paratuberculosis viability

Low pH and salt are two factors contributing to the inactivation of bacterial pathogens during a 60-day curing period for cheese. The kinetics of inactivation for Mycobacterium avium subsp. paratuberculosis strains ATCC 19698 and Dominic were measured at 20 degrees C under different pH and NaCl conditions commonly used in processing cheese. The corresponding D values (decimal reduction times; the time required to kill 1 log(10) concentration of bacteria) were measured. Also measured were the D values for heat-treated and nonheated M. avium subsp. paratuberculosis in 50 mM acetate buffer (pH 5.0, 2% [wt/vol] NaCl) and a soft white Hispanic-style cheese (pH 6.0, 2% [wt/vol] NaCl). Samples were removed at various intervals until no viable cells were detected using the radiometric culture method (BACTEC) for enumeration of M. avium subsp. paratuberculosis. NaCl had little or no effect on the inactivation of M. avium subsp. paratuberculosis, and increasing NaCl concentrations were not associated with decreasing D values (faster killing) in the acetate buffer. Lower pHs, however, were significantly correlated with decreasing D values of M. avium subsp. paratuberculosis in the acetate buffer. The D values for heat-treated M. avium subsp. paratuberculosis ATCC 19698 in the cheese were higher than those predicted by studies done in acetate buffer. The heat-treated M. avium subsp. paratuberculosis strains had lower D values than the nonheated cells (faster killing) both in the acetate buffer (pH 5, 2% [wt/vol] NaCl) and in the soft white cheese. The D value for heat-treated M. avium subsp. paratuberculosis ATCC 19698 in the cheese (36.5 days) suggests that heat treatment of raw milk coupled with a 60-day curing period will inactivate about 10(3) cells of M. avium subsp. paratuberculosis per ml.

A meta-analysis of antimycobacterial therapy for Crohn's disease

OBJECTIVE

Various therapies have been studied for the treatment of Crohn's disease, including antimycobacterial therapy. Meta-analysis was used to evaluate the effect of antimycobacterial therapy in patients with Crohn's disease.

METHODS

Randomized, controlled trials comparing antimycobacterial therapy with placebo were identified. Key outcome data were abstracted and the results were pooled to yield odds ratios for maintenance of remission in treated versus control groups.

RESULTS

A total of eight randomized trials were identified. Six trials were fully published and were included in the primary analysis. Two trials used antimycobacterial therapy in combination with corticosteroids to induce remission in patients with active Crohn's disease, followed by maintenance therapy with antimycobacterial agents. In these trials, control patients received corticosteroids to induce remission but no antimycobacterial therapy. Pooling of these trials yielded an odds ratio of maintenance of remission in treatment versus control of 3.37 (95% confidence interval [CI], 1.38-8.24) in favor of antimycobacterial therapy. The remaining four trials used antimycobacterial therapy combined with standard therapy in patients with Crohn's disease. In these trials, control patients received standard therapy alone. Pooling of these trials yielded an odds ratio of maintenance of remission in treatment versus control of 0.69 (95% CI, 0.39-1.21) in favor of standard therapy.

CONCLUSIONS

These results suggest that antimycobacterial therapy is effective in maintaining remission in patients with Crohn's disease after a course of corticosteroids combined with antimycobacterial therapy to induce remission. Treatment of Crohn's disease with antimycobacterial therapy does not seem to be effective without a course of corticosteroids to induce remission. Because of the small number of studies included in this meta-analysis, the results should be interpreted with caution.

Effect of rifaximin on intestinal bacterial overgrowth in Crohn's disease as assessed by the H2-Glucose Breath Test

The occurrence of intestinal bacterial overgrowth in patients with Crohn's Disease (CD) has been described and antimicrobial treatment has been shown to be effective in reversing this condition. However, the mechanisms underlying the efficacy of antimicrobial therapy are still only partially known. The aim of the present study was to evaluate the effect of a non-absorbable antibiotic (rifaximin) in comparison to placebo on bacterial overgrowth in patients with CD.

METHODS

Fourteen patients with inactive CD of the ileum and bacterial overgrowth, as assessed by the hydrogen breath test, were blindly allocated to receive rifaximin (1200 mg/day) or placebo t.i.d. for one week. A hydrogen breath test, and clinical and biochemical parameters were further performed 14 days and 30 days after starting treatment.

RESULTS

After 14 days, the hydrogen breath test proved to be negative in seven out of seven patients treated with rifaximin (p < 0.05), and in two out of seven in the placebo group (p = ns). After 30 days, the hydrogen breath test was positive in all patients of the rifaximin and placebo group, respectively. No changes in the CDAI score were documented in any patients.

CONCLUSIONS

Short-term administration of rifaximin is effective in the therapy of bacterial overgrowth in patients with inactive CD of the ileum, thus suggesting that the control of luminal bacterial growth could be useful in the management of these patients. However, since we observed a decline with time in this positive effect, further studies are needed to identify the most appropriate therapeutic strategies.

Development of a transposon mutagenesis system for Mycobacterium avium subsp. paratuberculosis

Mycobacterium avium subspecies paratuberculosis, a slow-growing Mycobacterium, is the causative agent of Johne's disease. Although M. paratuberculosis is difficult to manipulate genetically, our laboratory has recently demonstrated the ability to introduce DNA into these bacteria by transformation and phage infection. In the current study we develop the first transposon mutagenesis system for M. paratuberculosis using the conditionally replicating mycobacteriophage phAE94 to introduce the mycobacterial transposon Tn5367. Southern blotting and sequence analysis demonstrated that the transposon insertion sites are distributed relatively randomly throughout the M. paratuberculosis genome. We constructed a comprehensive bank of 5620 insertion mutants using this transposon. The transposition frequency obtained using this delivery system was 1.0 x 10(-6) transposition events per recipient cell. Auxotrophic mutants were observed in this library at a frequency of 0.3%.

Development of a firefly luciferase-based assay for determining antimicrobial susceptibility of Mycobacterium avium subsp. paratuberculosis

Paratuberculosis (Johne's disease) is a fatal disease of ruminants for which no effective treatment is available. Presently, no drugs against Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis), the causative agent of Johne's disease, are approved for use in livestock. Additionally, M. paratuberculosis has been linked to a human chronic granulomatous ileitis (Crohn's disease). To assist in the evaluation of antimicrobial agents with potential activity against M. paratuberculosis, we have developed a firefly luciferase-based assay for the determination of drug susceptibilities. The microorganism used was M. paratuberculosis K-10(pYUB180), a clinical isolate carrying a plasmid with the firefly luciferase gene. The MICs determined by the broth macrodilution method were as follows: amikacin, 2 microg/ml; Bay y 3118, 0.015 microg/ml; clarithromycin, 1.25 microg/ml; D-cycloserine, 25 microg/ml; ethambutol, 20 microg/ml; and rifabutin, 0.5 microg/ml. The strain was resistant to isoniazid and kanamycin. The results obtained by the luciferase assay were identical or fell within 1 doubling dilution. These results suggest that a combination of amikacin, clarithromycin, and rifabutin may be the most efficacious therapy for the treatment of M. paratuberculosis infections and that the use of fluoroquinolone class of antibiotics deserves further consideration. We demonstrate that the luciferase drug susceptibility assay is reliable for M. paratuberculosis and gives results within 7 days, whereas the broth macrodilution method requires 14 days.

Ovine Johne's disease: the risk associated with sheep imported into Western Australia

OBJECTIVE

To assess the risk of Johne's disease not being detected in sheep imported from New South Wales into Western Australia.

DESIGN

A stochastic simulation model.

PROCEDURE

The process of importing sheep was broken down into steps and numbers or probabilities assigned to each. Controls on the movement of sheep included surveillance tests in source flocks and serological tests on sheep in consignments before and after transportation to Western Australia. The model calculated the risk of occurrence of Johne's disease in Western Australia and the success of the agar gel immunodiffusion test in identifying consignments with infected sheep.

RESULTS

Negative surveillance tests in source flocks reduced the risk to about one twentieth of that when no surveillance tests were required. On average, Johne's disease was predicted to be introduced once in every 3 to 7 years when no testing of either the source flock or the sheep in consignments was required. When negative surveillance tests only were required the interval increased to once in every 63 to 111 years and, with the additional requirement that all sheep in each consignment must have a negative test before and after transport, the interval further increased to once in every 125 to 333 years. When only sheep in consignments were tested, the interval was calculated to be 8 to 14 years.

CONCLUSION

A requirement that imports be derived from flocks which had negative surveillance tests to Johne's disease would provide significantly greater protection for the sheep industry in Western Australia.

Identification of a Crohn's disease specific transcript with potential as a diagnostic marker

BACKGROUND

A long time goal of the medical research community has been the identification of a reliable and valid marker for Crohn's disease.

AIM

To identify differences in the genetic expression patterns of healthy and diseased tissues.

METHOD

The RNA arbitrarily primed polymerase chain reaction (RAP-PCR) procedure was modified to improve its potential to identify clinical markers in heterogeneous RNA populations.

RESULTS

With this procedure, a 1065 bp PCR product associated with the inflammation that occurs in Crohn's disease was identified, cloned and sequenced. Northern blot hybridisations showed that this novel sequence originates from a unique RNA species of 3.1 kb. Dot blot hybridisations clearly showed that this RNA species was specific to Crohn's disease. Moreover, its abundance seemed to correlate with the severity of inflammation. Finally, this RNA species was also detected in macroscopically normal areas from Crohn's disease specimens, suggesting that it appears either early during the disease or at least before severe manifestations.

CONCLUSION

This finding of a 3.1 kb RNA species permits the discrimination of Crohn's disease manifestations. Although further clinical work is required, this transcript appears to have definite potential as a diagnostic marker.

Thermal tolerance of Mycobacterium paratuberculosis

D values (decimal reduction time; the time required to kill 1 log concentration of bacteria) were determined for both human and bovine strains (Dominic, Ben, BO45, and ATCC 19698) of Mycobacterium paratuberculosis in 50 mM lactate solution (pH 6.8) and in milk at four temperatures (62, 65, 68, and 71 degrees C). Viable M. paratuberculosis organisms were quantified by a radiometric culture method (BACTEC). Thermal death curves for the M. paratuberculosis strains tested were generally linear, with R2 of > or = 0.90, but a few curves (R2, 0.80 to 0.90) were better described by a quadratic equation. The human strains (Dominic and Ben) had similar D values in milk and in lactate solution. However, D values for the bovine strains (BO45 and ATCC 19698) were significantly different depending on the menstruum. D values for low-passage clinical strains (Dominic, Ben, and BO45) were lower than those of the high-passage laboratory strain (ATCC 19698). The D value based on pooled data for clinical strains of M. paratuberculosis in milk at 71 degrees C (D71 degrees C) was 11.67 s. Pooled D62 degrees C, D65 degrees C, and D68 degrees C of clinical M. paratuberculosis strains in milk were 228.8, 47.8, and 21.8 s, respectively. The Z value (the temperature required for the decimal reduction time to traverse 1 log cycle) of clinical strains in milk was 7.11 degrees C. The D values of clumped and single M. paratuberculosis cells were not significantly different. The D values of all M. paratuberculosis strains tested were considerably higher than those published for Listeria, Salmonella, and Coxiella spp. and estimated for Mycobacterium bovis, indicating that M. paratuberculosis is more thermally tolerant. This study supports the premise that M. paratuberculosis may survive high-temperature, short-time pasteurization when the initial organism concentration is greater than 10(1) cells/ml.

Johne's disease: a hidden threat

Paratuberculosis, which is also known as Johne's disease, is a chronic, progressive enteric disease of ruminants caused by infection with Mycobacterium paratuberculosis. Cattle become infected with M. paratuberculosis as calves but often do not develop clinical signs until 2 to 5 yr of age. The clinical disease is characterized by chronic or intermittent diarrhea, emaciation, and death. Although animals with clinical disease are often culled from the herd, animals with subclinical paratuberculosis may cause economic losses because of reduced milk production and poor reproductive performance. Although the economic impact of paratuberculosis on the national cattle industry has not been determined, it is estimated to exceed $1.5 billion/yr. The diagnosis of subclinical paratuberculosis is difficult. Bacteriologic culture is the most definitive method of diagnosis, but culture is time consuming and labor intensive. Serological assays are not very useful because animals do not develop an antibody response until the clinical stages of disease. Development of assays to measure cell-mediated immunity is critical to accurate detection of paratuberculosis in subclinically infected animals. Although not considered a zoonotic agent, M. paratuberculosis has been identified in intestinal biopsy tissue from patients with Crohn's disease, an inflammatory enteritis in humans. Currently, the potential human health risk is being addressed by research evaluating pasteurization of dairy products in the US.

Innovative approaches to novel antibacterial drug discovery

Increasing antibiotic resistance in microorganisms and new emerging pathogens have become a major problem in our society. Rising to satisfy this urgent medical need is a recent confluence of powerful new drug discovery technologies: combinatorial chemistry; sequence and functional genomic analysis; and novel methods of high-throughput screening. The combination of these technologies will bring to bear untapped power in the search for new antimicrobials.

Mycobacterium paratuberculosis: a potential food-borne pathogen?

Mycobacterium paratuberculosis commonly infects dairy cattle, leading to Johne's disease, which is also known as paratuberculosis. The infection is chronic progressive, and incurable. As the infection progresses, excretion of M. paratuberculosis in feces and milk occurs, and the bacterium spreads through the blood to multiple internal organs. Consequently, raw products originating from cattle may harbor M. paratuberculosis. Thermal treatments, such as pasteurization, are commonly relied on to kill food-borne bacterial pathogens that can infect humans. The small number of studies conducted to determine the thermal resistance of M. paratuberculosis suggest that it is less susceptible to destruction by heat killing than are milkborne zoonotic bacterial pathogens such as Listeria spp. or Mycobacterium bovis. Published reports concerning the thermal resistance of M. paratuberculosis in milk are reviewed herein, and key issues concerning the efficacy of pasteurization for elimination of M. paratuberculosis from milk are summarized.

Ultrastructural localization of osteopontin immunoreactivity in phagolysosomes and secretory granules of cells in human intestine

A post-embedding ultrastructural immunogold method was used to detect osteopontin in human intestinal biopsies with special emphasis on secretory and phagocytic organelles. Osteopontin immunoreactivity was localized to phagolysosomes of macrophages, fibroblasts, absorptive epithelial cells of the small intestine and Paneth cells. The mucigen secretory granules and Golgi structures of mucous epithelial cells of the small intestinal epithelium contained osteopontin, but secretory granules of numerous other cells, including Paneth cells, did not. Extracellular and phagocytosed Tropheryma whippelii within macrophage phagolysosomes also bound osteopontin. These localizations are supportive of a role for osteopontin in phagocytic and some secretory cell functions in human intestine.

A multiplex polymerase chain reaction assay for the detection of Mycobacterium paratuberculosis DNA in Crohn's disease tissue

BACKGROUND

Mycobacterium paratuberculosis is implicated as a possible cause of Crohn's disease. However, due to lack of an appropriate diagnostic method, this has been a subject of significant controversy. Our aim was therefore to develop a multiplex polymerase chain reaction (MPCR) for the detection of M. paratuberculosis DNA in Crohn's disease tissue.

METHODS

Biopsy samples were collected by endoscopic forceps from terminal ileum, and genomic DNA was isolated. M. paratuberculosis-specific marker genes were amplified by using the present MPCR method.

RESULTS

Here we report a new MPCR for detection of M. paratuberculosis DNA in Crohn's disease tissue. In this technique two genetic markers, IS900 and a newly described specific marker of MP2, were amplified in a single tube simultaneously. The method was evaluated using biopsy specimens from 10 Crohn's disease patients, 6 ulcerative colitis patients, and 21 irritable bowel syndrome patients. The patients were characterized by using standard clinical and histologic observations. The present MPCR method could not detect M. paratuberculosis DNA in the biopsy specimens. However, the marker genes were amplified from the samples that were spiked with M. paratuberculosis before DNA extraction. The marker genes were also not detected in 10 closely related mycobacterial strains and human genomic DNA.

CONCLUSIONS

The present MPCR method is highly specific and can detect M. paratuberculosis DNA more reliably. These findings do not support an aetiologic role of M. paratuberculosis in Crohn's disease.

Effects of gamma interferon and nitric oxide on the interaction of Mycobacterium avium subsp. paratuberculosis with bovine monocytes

In this study, we examined the effects of recombinant bovine gamma interferon (rIFN-gamma) and nitric oxide (NO) on the interaction of M. avium subsp. paratuberculosis with bovine monocytes. Monocytes pretreated with rIFN-gamma exhibited slightly increased phagocytosis of M. avium subsp. paratuberculosis and modest inhibition of the intracellular growth of this microorganism. The number of viable intracellular bacilli decreased earlier in rIFN-gamma-pretreated monocytes than in control monocytes. After infection with M. avium subsp. paratuberculosis, NO was not constitutively released, but NO release from infected monocytes was induced by treatment with rIFN-gamma or with rIFN-gamma and lipopolysaccharide (LPS). Release of nitric oxide was inhibited by addition of N(G)-monomethyl-L-arginine; however, inhibition of nitric oxide did not alter the pattern of intracellular survival of M. avium subsp. paratuberculosis in rIFN-gamma-treated bovine monocytes. Although chemically generated nitric oxide killed M. avium subsp. paratuberculosis in a cell-free system in vitro, the amount of nitric oxide required was far greater than that released from infected monocytes stimulated with rIFN-gamma and LPS. Our data suggest that rIFN-gamma activates M. avium subsp. paratuberculosis-infected bovine monocytes to release nitric oxide but only modestly increases antimycobacterial activity of monocytes against this organism. This may be due, in part, to the fact that the amount of nitric oxide produced by rIFN-gamma-activated bovine monocytes is insufficient to kill intracellular M. avium subsp. paratuberculosis bacilli in vitro.

Enteric Microflora in IBD: Pathogens or Commensals?

: Both pathogenic and normal enteric microflora can induce and perpetuate chronic intestinal inflammation with systemic manifestations in genetically susceptible hosts. At the present time, there is no convincing indication that the majority of cases of ulcerative colitis or Crohn's disease is caused by persistent infection by Mycobacterium paratuberculosis, measles, Listeria monocytogenes, or Helicobacter species, but this possibility remains a valid hypothesis. Transient infection with any of a number of pathogens including upper respiratory tract infections and common enteric pathogens could provide one of the environmental triggers that initiate or reactivate IBD, which is then perpetuated in susceptible hosts by resident (not pathogenic) commensal luminal bacteria. Recent results in animal models demonstrate the absence of colitis, gastritis, and arthritis in a sterile (germ-free) environment, showing the importance of resident bacteria as persistent antigenic stimuli in the genetically susceptible hosts. Furthermore, there is an indication that not all normal luminal bacteria have equal capacities to induce mucosal injury, since some species can induce inflammation (Bacteroides), some are neutral (E. coli) and others may be protective (Lactobacilli). These observations have important therapeutic implications, such that altering luminal bacterial components and thereby decreasing the persistent antigenic drive offer alternative or adjuvant approaches to ongoing efforts to block mucosal immune responses to these stimuli.