Microflora reactive IL-10 producing regulatory T cells are present in the colon of IL-2 deficient mice but lack efficacious inhibition of IFN-gamma and TNF-alpha production.

BACKGROUND: Inflammatory bowel disease in interleukin 2 (IL-2) deficient (IL-2(-/-)) mice is triggered by the intestinal microflora and mediated by CD4(+) T cells. AIMS: To determine the characteristics of microflora specific intestinal T cells, including migration and cytokine production. METHODS: Intestinal T cell populations and cytokine mRNA expression of specific pathogen free (SPF) and germ free (GF) IL-2(-/-) and IL-2(+/+) mice were compared by flow cytometry and reverse transcription-polymerase chain reaction. Cytokine production of intestinal mononuclear cells on stimulation with microflora antigens was assessed by ELISA. In vivo migration of T cells was assessed by adoptive transfer of (51)Cr labelled CD4(+)CD25(-)alpha beta(+) T cells. The ability of intestinal T cell lines to promote colitis was determined by adoptive transfer experiments. RESULTS: SPF IL-2(-/-) mice produced higher interferon gamma (IFN-gamma) and tumour necrosis factor alpha mRNA levels than GF IL-2(-/-) mice, which was accompanied by an increased number of CD4(+)alpha beta T cells in the colon. Tracking of (51)Cr labelled and adoptively transferred T cells revealed an increased MAdCAM-1 dependent but VCAM-1 independent recruitment of these cells into the colon of SPF IL-2(-/-) mice. Colon lamina propria lymphocytes (LPL) from SPF IL-2(-/-) mice showed increased spontaneous IFN-gamma production in vitro. On stimulation with bacterial microflora antigens, intraepithelial lymphocytes and LPL did not produce IFN-gamma, but high quantities of IL-10, which did not suppress IFN-gamma production. Bacterial antigen specific cell lines established from colon LPL of SPF IL-2(-/-) mice with colitis showed a regulatory T cell-like cytokine profile and only marginally modulated the course of colitis and survival of IL-2(-/-) mice. CONCLUSIONS: Our results suggest that microflora reactive regulatory T cells are present in the colon of SPF IL-2(-/-) mice. However, IL-10 produced by these cells did not significantly modulate a possible secondary proinflammatory CD4 Th1 cell population to produce IFN-gamma.

Interferon consensus sequence binding protein confers resistance against Yersinia enterocolitica.

Interferon consensus sequence binding protein (ICSBP)-deficient mice display enhanced susceptibility to intracellular pathogens. At least two distinct immunoregulatory defects are responsible for this phenotype. First, diminished production of reactive oxygen intermediates in macrophages results in impaired intracellular killing of microorganisms. Second, defective early interleukin-12 (IL-12) production upon microbial challenge leads to a failure in gamma interferon (IFN-gamma) induction and subsequently in T helper 1 immune responses. Here, we investigated the role of ICSBP in resistance against the extracellular bacterium Yersinia enterocolitica. ICSBP(-/-) mice failed to produce IL-12 and IFN-gamma, but also IL-4, after Yersinia challenge. In addition, granuloma formation was highly disturbed in infected ICSBP(-/-) mice, leading to multiple necrotic abscesses in affected organs. Consequently, ICSBP(-/-) mice rapidly succumbed to acute Yersinia infection. In vitro treatment of spleen cells from ICSBP(-/-) mice with recombinant IL-12 (rIL-12) or rIL-18 in combination with a second stimulus resulted in IFN-gamma induction. In experimental therapy of infected ICSBP(-/-) mice, we observed that administration of rIL-12 induced IFN-gamma production which was associated with improved resistance to Yersinia. In contrast, treatment with rIL-18 failed to enhance endogenous IFN-gamma production but nevertheless reduced bacterial burden in ICSBP(-/-) mice. Although cytokine therapy with rIL-12 or rIL-18 ameliorated the course of Yersinia infection in ICSBP(-/-) mice, both cytokines failed to completely restore impaired immunity. Taken together, the results indicate that the transcription factor ICSBP is essential for efficient host immune defense against Yersinia. These results are important for understanding the complex host immune responses in bacterial infections.

DNA immunization confers systemic, but not mucosal, protection against enteroinvasive bacteria.

Naked plasmid DNA (pRc/Y-hsp60) with a cytomegalovirus promoter and a sequence encoding Yersinia enterocolitica 60-kDa heat shock protein (Y-HSP60) was used for vaccination. After intramuscular injection of pRc/Y-hsp60, Y-hsp60 mRNA could be detected by reverse transcription-PCR in muscle, liver and spleen. A single immunization with pRc/Y-hsp60 induced significant Y-HSP60-specific T cell responses after 1 week. IFN-gamma production by spleen cells upon stimulation with Y-HSP60 was strictly dependent on the presence of CD4+ T cells, indicating the generation of a Th1 response upon DNA immunization. DNA immunization in addition induced strong Y-HSP60-specific IgG2a, weak IgG1, but not IgA antibodies. Immunization of BALB/c and C57BL/6 mice with pRc/Y-hsp60 conferred protection against disseminated Y. enterocolitica infection in spleen, but not at the site of mucosal entry, the Peyer's patches. Furthermore, pRc/Y-hsp60 vaccination did not induce cross-protection against related pathogens. Vaccination of beta2-microglobulin- and H2-I-Abeta-deficient mice was not protective, suggesting that both CD4+ and CD8+ T cells are required for protective immunity induced by DNA vaccination.

Cytokine mRNA expression in intestinal tissue of interleukin-2 deficient mice with bowel inflammation.

BACKGROUND: Mice deficient in interleukin-2 (IL-2) develop inflammatory bowel disease resembling ulcerative colitis in humans. Recent studies provided evidence that alpha beta T cells, particularly CD4 T cells, rather than B cells, are involved in the pathogenesis of bowel inflammation of IL-2 deficient mice. AIM: To analyse the pattern of expression of cytokine mRNA in intestinal tissue of normal and IL-2 deficient mice. METHODS: Expression of beta-actin, IL-1 alpha, IL-1 beta, IL-6, IL-10, tumour necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma) and transforming growth factor beta 1 (TGF-beta 1) mRNA was analysed in colon and small intestinal tissue of both IL-2 deficient (IL-2-/-) mice and normal (wild type) litter mates (IL-2+/+) at different ages by using qualitative, as well as semiquantitative, competitive reverse transcription polymerase chain reaction (RT-PCR). Results were correlated with the phase of progression of the disease, as determined by histology. RESULTS: IL-2-/- mice had expressed low levels of IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, and IFN-gamma mRNA in the colon by 1.5 weeks of age. In advance of the development of histologically and clinically detectable bowel inflammation, expression of IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, IFN-gamma, and IL-10, but not TGF-beta 1, mRNA increased in the colon of IL-2 deficient mice. In contrast, IL-2+/+ mice expressed TGF-beta 1 mRNA in colon tissue at 13 and 23 weeks of age, but not IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, IL-10, or IFN-gamma mRNA. Levels of expression of cytokine mRNA in tissue from the small intestine were comparable in IL-2-/- and IL-2+/+ mice. CONCLUSIONS: Bowel inflammation in IL-2 deficient mice is preceded by an increase in IL-1 alpha, IL-1 beta, TNF-alpha, and IFN-gamma mRNA expression in colon tissue. Low levels of TGF-beta 1, but high levels of IL-1 alpha, IL-1 beta, IL-6, TNF-alpha, IFN-gamma, and IL-10 mRNA expression correlate with the manifestation of severe colitis, and suggest that T cells and macrophages are involved in bowel inflammation of IL-2 deficient mice.