Dendritic cells "in vivo": their role in the initiation of intestinal immune responses

Increased S-nitrosylation and proteasomal degradation of caspase-3 during infection contribute to the persistence of adherent invasive Escherichia coli (AIEC) in immune cells

Adherent invasive Escherichia coli (AIEC) have been implicated as a causative agent of Crohn’s disease (CD) due to their isolation from the intestines of CD sufferers and their ability to persist in macrophages inducing granulomas. The rapid intracellular multiplication of AIEC sets it apart from other enteric pathogens such as Salmonella Typhimurium which after limited replication induce programmed cell death (PCD). Understanding the response of infected cells to the increased AIEC bacterial load and associated metabolic stress may offer insights into AIEC pathogenesis and its association with CD. Here we show that AIEC persistence within macrophages and dendritic cells is facilitated by increased proteasomal degradation of caspase-3. In addition S-nitrosylation of pro- and active forms of caspase-3, which can inhibit the enzymes activity, is increased in AIEC infected macrophages. This S-nitrosylated caspase-3 was seen to accumulate upon inhibition of the proteasome indicating an additional role for S-nitrosylation in inducing caspase-3 degradation in a manner independent of ubiquitination. In addition to the autophagic genetic defects that are linked to CD, this delay in apoptosis mediated in AIEC infected cells through increased degradation of caspase-3, may be an essential factor in its prolonged persistence in CD patients.

Concurrent exposure to thermal stress and oral Ag induces intestinal sensitization in the mouse by a mechanism of regulation of IL‐12 expression

The mechanism of food allergy remains unclear. The absorption of intact protein Ag into the intestinal tissue is a prerequisite in the development of intestinal sensitization. Previous studies indicate that thermal stress compromises the intestinal barrier function. Mice were concurrently exposed to thermal stress and oral Ag. Intestinal sensitivity, levels of serum-specific IgE, IL-4 and INF-gamma were assessed. Intestinal dendritic cell, Th1 and Th2 functions were determined. The mice that were treated with thermal stress and oral Ag showed high levels of serum Ag-specific IgE, intestinal mast cell activation in response to oral Ag challenge, suppression of IL-12 expression in the intestinal dendritic cells, inhibition of T-bet expression and Th1 function and marked increases in (GATA)3 expression and Th2 function. Mice exposed to thermal stress alone or oral Ag alone did not show any signs of the intestinal sensitization. Pretreatment with IL-12 inhibited the intestinal sensitization induced by the concurrent exposure to thermal stress and Ag gavage. We conclude that although Ag absorption is essential, Ag absorption alone is insufficient; other accessory factors that can disturb the local immune homeostasis are also required for the induction of intestinal sensitization. The present study illustrates that concurrent exposure to thermal stress and oral Ag can prove to be a factor in the induction of intestinal sensitization by a mechanism of regulating IL-12 expression.

Chronic psychological stress in rats induces intestinal sensitization to luminal antigens

There is increasing evidence that stress plays a role in the pathophysiology of chronic intestinal disorders, but the mechanisms remain unclear. Previous studies in rats have revealed that stress decreases gut barrier function and allows excessive uptake of luminal material. Here, we investigated whether chronic psychological stress acts to induce sensitization of intestinal tissues to oral antigens. Rats were subjected to 1 hour per day of water avoidance stress or sham stress daily for 10 days, and horseradish peroxidase (HRP) was delivered by gavage on day 5. Studies to determine sensitization were conducted on day 20. All stressed rats developed HRP-specific IgE antibodies, antigen-induced intestinal secretion, and increased numbers of inflammatory cells in gut mucosa. Luminal HRP was absorbed more readily by enterocytes of stressed animals. In addition, stressed rats had increased expression of interleukin-4 and decreased expression of interferon-gamma in gut mucosa, a cytokine profile that is typical of allergic conditions. Treatment of stressed rats with an antagonist to corticotropin-releasing hormone (previously shown to inhibit stress-enhanced gut permeability) eliminated the manifestations of intestinal hypersensitivity. Our results indicate that the presence of oral antigen during chronic psychological stress alters the immune response (to sensitization rather than oral tolerance) and causes subsequent antigen-induced gut pathophysiology.

Differentiation to the CCR2+ inflammatory phenotype in vivo is a constitutive, time-limited property of blood monocytes and is independent of local inflammatory mediators

It is proposed that CCR2+ monocytes are specifically recruited to inflammatory sites, whereas CCR2- monocytes are recruited to normal tissue to become resident macrophages. Whether these subsets represent separate lineages, how differential trafficking is regulated and whether monocytes undergo further differentiation is uncertain. Using a mouse model of autoimmune uveoretinitis we examined monocyte trafficking to the inflamed retina in vivo. We show that bone marrow-derived CD11b+ F4/80- monocytes require 24 to 48 h within the circulation and lymphoid system before acquiring the CCR2+ phenotype and trafficking to the inflamed retina is enabled. This phenotype, and the capacity to traffic were lost by 72 h. Monocyte CCR2 expression followed a similar time course in normal mice indicating that differentiation to an inflammatory phenotype is a constitutive, time-limited property, independent of local inflammatory mediators. Phenotypic analysis of adoptively transferred cells indicated that circulating inflammatory monocytes also differentiate into CD11c+ and B220+ dendritic cells and F4/80+ tissue macrophages in vivo. Our data supports the hypothesis of continuous extravasation and progressive differentiation over time of inflammatory monocytes in the circulation rather than replication within the actively inflamed tissue, and supports the concept of myeloid dendritic cell differentiation from trafficking monocytes under physiological conditions in vivo.

Serum antibody reactivity against recombinant PrtC of Porphyromonas gingivalis following periodontal therapy

OBJECTIVES

In 34 patients with chronic periodontitis, the presence of IgA, IgG, and IgG subclass serum antibodies against recombinant PrtC (rPrtC) of Porphyromonas gingivalis was assessed by immunoblot analysis 24 months after therapy.

METHODS

rPrtC was produced from P. gingivalis ATTC 33277 using the plasmid pGEX-2T. In addition, intraoral colonization with P. gingivalis was detected by PCR in subgingival plaque and swab samples from buccal mucosae, tonsils and tongue at baseline, 10 d, and 3, 6, 9, 12, 18, and 24 months.

RESULTS

All patients were found to harbor P. gingivalis in the oral cavity at least once during the observation period. The identified antibody responses against the rPrtC of P. gingivalis were IgA (97%, i.e. 33/34 patients) and IgG (100%, i.e. 34/34), with an IgG subclass distribution of IgG2 (65%, i.e. 22/34 patients) > IgG3 (47%, i.e. 16/34) > IgG1 (38%, i.e. 13/34) > IgG4 (29%, i.e. 10/34). Anti-rPrtC IgA and IgG antibody reactivity was found in all but one patients (anti-rPrtC IgA negative), who tested negative for P. gingivalis at all of the assessed intraoral sites for at least 6 months before sera collection. There was no association between IgG subclass reactivity against the rPrtC of P. gingivalis and progression of periodontal attachment loss.

CONCLUSION

The results indicated that anti-rPrtC IgA and IgG antibodies may serve as an indicator for past or present intraoral colonization with P. gingivalis.

Phenotypic diversity of antigen-presenting cells in ovine-afferent intestinal lymph

The phenotypic and functional repertoire of antigen-presenting cells (APCs) remains incompletely characterized, particularly during the migratory phase of their life history, when these cells leave peripheral tissues and travel via afferent lymphatic vessels to regional lymph nodes. Lymphatic cannulation procedures were used to collect ovine APCs as they migrated from the mucosa of the small intestine to regional lymph nodes. A panel of 19 new monoclonal antibodies (mAbs) was produced to characterize surface molecules expressed on APCs by means of two-color flow cytometry and microscopy. Two broad patterns of mAb reactivity were evident. Twelve mAbs reacted almost exclusively with cells in the APC-gated region, because all these mAbs stained < 3% of cells in the lymphocyte-gated region. Within this group, some mAbs identified distinct subsets of dendritic cells (DCs). The second group of seven mAbs displayed high-intensity staining on cells in the APC-gated region but also reacted with variable numbers (4-26%) of cells in the lymphocyte-gated region. This indicates that molecules recognized by these mAbs are highly expressed on APCs but also occur on other lineages. When new mAbs were analyzed by two-color flow cytometry of cells in afferent intestinal lymph, a wide range of differences in reactivity were observed, especially on CD11b(+), CD11c(+), CD4(+), MHCII(+), and gammasigmaTCR(+) cells. Although molecular specificities of mAbs reported here remain undefined, marked heterogeneity of staining patterns indicates considerable phenotypic, and probably functional, diversity within APC population in afferent intestinal lymph. MAbs reported here will provide useful tools to explore these features further.

Antigenic specificity of gingival crevicular fluid antibody to Actinobacillus actinomycetemcomitans

Elevated antibody levels to periodontopathogens in GCF have been identified and used as support for local antibody synthesis in periodontitis. This study examined both cross-sectional and longitudinal GCF samples for the antigenic specificity of antibody in the fluid. GCF samples were collected from each tooth of 27 periodontitis patients infected with A. actinomycetemcomitans. Levels of IgG antibody in the GCF were assessed by means of an ELISA and compared with serum for determination of local elevations. A proportion of those GCF samples that exhibited significantly elevated antibody were examined by Western immunoblotting to outer membrane antigens from A. actinomycetemcomitans. Homologous sera were also examined for comparison of antibody specificities. Of the sites with elevated IgG antibody, 87% were colonized by A. actinomycetemcomitans; however, 46% of sites with A. actinomycetemcomitans infection did not have elevated antibody. Cross-sectional studies identified a 78 to 100% agreement between the antibody specificities in GCF and those in serum. Additionally, patterns of antibody reactivity in both GCF and serum in the subjects were often very distinctive. Longitudinal alterations in GCF antibody were examined in 15 patients through a monitoring interval of up to 2 years and showed a general conservation of specificities. However, 7/15 patients exhibited a definite acquisition of different antibody specificities during the monitoring. These results describe a relationship between elevated local antibody and A. actinomycetemcomitans infection. Furthermore, the antibody specificities in serum appear to reflect generally the local response to this pathogen.