Genetically engineered Lactococcus lactis secreting murine IL-10 modulates the functions of bone marrow-derived dendritic cells in the presence of LPS.

Oral delivery of IL-10 by genetically modified Lactococcus lactis (LL-pTmIL10) has been shown to efficiently reduce intestinal inflammation in mice with chronic colitis, but the mechanisms involved have not been elucidated. It has been suggested that IL-10 controls intestinal inflammation by inhibiting microbe-induced activation of dendritic cells. We therefore investigated whether LL-pTmIL10 can modulate the functions of bone marrow-derived dendritic cells (BM-DC) responding to LPS. Incubation of these cells with LL-pTmIL10 or with the control strain LL-pTREX reduced their ability to activate allogeneic T-cell proliferation. However, in contrast to LL-pTREX, LL-pTmIL10 inhibited the LPS-stimulated secretion of MCP-1 by BM-DC and reduced the synergistic up-regulation of IL-12/IL-23p40. In addition, LL-pTmIL10 treatment of LPS-stimulated BM-DC significantly inhibited their capacity to induce strong secretion of IL-17 by CD4+ T cells. Our data suggest that the beneficial effects of LL-pTmIL10 treatment during chronic colitis might involve inhibition of CD4+ Th17 cells and a reduced accumulation of these cells as well as other immune cells at the site of inflammation.

Murine trefoil factor 3 does not directly modulate LPS-mediated dendritic cell function.

Peptides of the trefoil factor family (TFF) are expressed along the gastro-intestinal tract. They protect mucous epithelia from damage and contribute to mucosal repair, which is essential for preventing inflammation. Moreover, it has been suggested that TFF2 and TFF3, in particular, play a role in regulating immune responses. Depending on their activation status, dendritic cells (DC) can initiate either tolerance or immunity. This study, by comparing LPS-induced maturation of mTFF3-treated DC and non-treated DC, investigated whether murine TFF3 directly regulated DC function. mTFF3-treated DC and non-treated DC did not differ phenotypically or functionally. Both populations expressed, both before and after LPS-stimulation, similar levels of co-stimulatory molecules and cytokines, and were both efficient stimulators of T-cells. Our results suggest that mTFF3 does not govern immune responses on the level of DC function.

Liver tolerance mediated by antigen presenting cells: fact or fiction?

Possible mechanisms by which liver antigen presenting cells (APC) may facilitate tolerance induction are discussed. Tolerance may be facilitated by a distinctive combination of factors, linked to the unique anatomical and microenvironmental features of the liver.

Expression of Ly49E and CD94/NKG2 on fetal and adult NK cells.

Murine NK cells express inhibitory receptors belonging to the Ly49 and CD94/NKG2 family. Ly49E and CD94 are the only NK cell receptor transcripts detectable in fetal NK cells. Still unproved is the surface expression of Ly49E on NK cells. Here we generated two novel mAbs, a mAb recognizing Ly49E with cross-reactivity to Ly49C, and a mAb against NKG2A/C/E. Ly49E was immunoprecipitated as a disulfide-linked homodimer with 46-kDa subunits. Removal of N-linked carbohydrates revealed a 31-kDa protein backbone. NKG2A was immunoprecipitated as a 38-kDa protein. Although the frequency of fetal NK cells expressing Ly49E was higher than 25%, it decreased drastically from 2 wk after birth. Phenotypic analysis showed that approximately 90% of fetal NK cells and approximately 50% of adult NK cells express high levels of CD94/NKG2. The remaining 50% of adult NK cells expressed low surface levels of CD94/NKG2. Expression of Ly49E and CD94/NKG2 was not restricted to NK cells, but was also observed on NK T and memory T cells. Functional analysis showed that sorted Ly49E(+) and CD94/NKG2(+) fetal NK cells could discriminate between MHC class I-positive and MHC class I-negative tumor cells. We also demonstrated that Ly49E becomes phosphorylated following pervanadate stimulation of fetal NK cells. The expression levels of Ly49E and CD94/NKG2 were similar in wild-type compared with beta(2)-microglobulin(-/-) mice. In conclusion, generation of mAbs against Ly49E and NKG2 extended the phenotypic and functional characterization of NK cells.

Langerhans cells that have matured in vivo in the absence of T cells are fully capable of inducing a helper CD4 as well as a cytotoxic CD8 response.

Langerhans cells (LCs) are immature dendritic cells (DCs) present in the skin epithelium. Upon Ag exposure, they migrate to the draining lymph nodes where they mature into potent stimulators of naive T cells. The aim of this study was to investigate the influence of T cells on LC migration and maturation. Therefore, the in vivo migration and maturation of LCs after sensitization with the hapten FITC was compared between C57BL/6 or BALB/c mice used as positive controls, and recombination activating gene (RAG) 1 knockout (-/-) mice or SCID mice used as T cell-deficient mice. Phenotypically, there was no difference between migrated LCs from RAG1-/- or SCID mice vs normal C57BL/6 or BALB/c mice: both populations of FITC+ cells had a dendritic morphology and a mature phenotype as they expressed high levels of MHC class II molecules and costimulatory molecules CD80, CD86, and CD54. Sorted migrated LCs of RAG1-/- or SCID mice were efficient stimulators of allogeneic T cells and Ag-specific CD4+ T cells. The same results were found if migrated LCs were fixed instead of irradiated, excluding the possibility that LCs derived from RAG1-/- or SCID mice would mature in the presence of T cells during the stimulation tests. Importantly, fixed migrated LCs of RAG1-/- mice were also efficient stimulators of cytotoxic CD8+ T cells. These data suggest that T cells are not required for full maturation of LCs.

Murine fetal natural killer cells are functionally and structurally distinct from adult natural killer cells.

Natural killer (NK) cell phenotype and activity was studied by analyzing uncultured and short-time-cultured murine NK cells from fetal day 17 spleen and thymus. In contrast to NK cells from adult mice, freshly sorted fetal NK cells did not contain NK receptor transcripts for Ly-49A, B, C/I, D, F, G2, or H. The only NK receptor transcripts that could be detected were Ly-49E and CD94. It is important that Ly-49E was present at a 10- to 30-fold higher level compared with uncultured NK cells from adult mice. After short-time interleukin-2 culture, the level of Ly-49E mRNA was comparable between fetal and adult NK cells. Functionally, fetal NK cells only killed MHC class I-negative tumor cells when activating NK receptors were cross-linked with antibody. We show that fetal NK cells are mature but are different from NK cells in adult mice regarding their NK cell receptor repertoire and function.