Sustained delayed-type hypersensitivity reaction after in vivo priming but successful induction of unresponsiveness after adoptive transfer of CD4+ effector T cells.

Potential reasons for weak effects of oral tolerance in the primed immune system are still under discussion. In the present study, impacts of oral antigen uptake were studied in adoptive transfer models using T cell receptor transgenic CD4(+) T cells allowing analysis of antigen-specific donor cells on single cell level. After in vivo priming and subsequent feeding, an antigen-specific delayed-type hypersensitivity reaction was sustained. Concomitantly, donor cells preferentially found in the draining lymph nodes remained at equal numbers. In contrast, adoptively transferred Th1 cells that migrated preferentially into spleen and liver became fewer upon feeding accompanied by a suppressed delayed-type hypersensitivity reaction. Thus, antigen-experienced cells did not seem to become generally resistant to tolerogenic stimuli. Our data suggest that besides a permanent inflammatory stimulus provided by the persisting antigen, diverse tissue distribution of in vivo-induced compared to adoptively transferred effector cells might interfere with oral tolerance in the experienced immune system.

In vivo modulation of antigen-experienced cells in response to high-dose oral antigen: deletion but no evidence for alterations in the cytokine phenotype.

Whether also antigen-experienced CD4(+) T cell populations undergo modulations upon oral antigen uptake supporting systemic unresponsiveness is still not fully understood. Using an adoptive transfer model with chicken ovalbumin (OVA)-specific T cells, we demonstrated that absolute numbers of transferred ex vivo-isolated CD4(+) memory T cells and in vitro-polarized T(h)1 cells considerably decrease within spleen and liver upon repetitive OVA feeding. As a consequence, these mice did not mount a delayed-type hypersensitivity reaction after OVA challenge. OVA-specific T(h)1 cells re-isolated from the liver showed augmented signs of apoptosis. However, there was no evidence that transferred effector or memory T cells acquired a regulatory phenotype, became anergic or underwent immune deviation. Our data suggest that oral antigen application does not induce alterations in the phenotype of CD4(+) effector and memory T cells. Instead, deletion of antigen-experienced CD4(+) T cells preferentially within the liver might be a major mechanism contributing to antigen-specific systemic unresponsiveness upon oral antigen uptake.

Adoptively transferred Th1 cell populations lose IFNgamma+ cells by cytokine down-regulation on single-cell level.

Against the background of effector T cell heterogenity in terms of their in situ cytokine expression, IFNgamma production has been argued to define distinct Th1 lineages: whereas IFNgamma- Th1 cells survive and differentiate in vivo, IFNgamma+ Th1 cells eventually undergo apoptosis. Alternatively, lineage commitment might not be directly associated with the actual IFNgamma production. To address this issue, we adoptively transferred in vitro-polarized Th1 cell populations. Although absolute numbers of total Th1 cells after 3 days in vivo remained unchanged, numbers of IFNgamma+ within the Th1 cells declined by approximately 50%. This was not affected by the initial frequencies of IFNgamma+ cells within the transferred Th1 cell populations and by the presence of the antigen. Arguing against positive selection of IFNgamma non-producers in vivo, cell division rates of IFNgamma+ and IFNgamma- Th1 cells were comparable. Our data suggest that the 'loss' of IFNgamma+ cells within the transferred Th1 cell population might be rather caused by down-regulation of the cytokine expression on single-cell level than by deletion of individual IFNgamma+ cells. Thus, our findings are more in line with the hypothesis that actual cytokine expression does not define distinct differentiation states and polarization-specific genes remain accessible also in IFNgamma- Th1 effector cells.

The spectrum of lymphoid subsets preferentially recruited into the liver reflects that of resident populations.

Intrahepatic lymphocytes (IHL) differ phenotypically from cells found in the peripheral blood or in lymphoid organs. The liver contains T-cells that are also found in lymphoid organs but a higher proportion of these T-cells compared to those in lymphoid organs express activation or memory markers and very few naïve T-cells are present within the liver. Furthermore, subsets such as NK and NK T-cells, which are detected at comparably lower levels within the lymphoid organs are increased within the liver. To investigate whether a preferential recruitment of certain lymphoid subsets from the circulation contributes to the composition of intrahepatic lymphocytes, we compared their frequency in the liver with their organ tropisms. CFSE-labeled murine lymphoid cells were injected intravenously and their distribution within liver and spleen was analyzed after 24 h. Especially CD45RB(low) memory T-cells, NK and NK T-cells, which are also present at high proportions within IHL, became predominantly recruited into the liver. In contrast, subsets such as naïve CD62L(high) T-cells and B-cells, which are predominantly represented within the lymphoid organs, preferentially migrated into the spleen. These findings indicate that the pattern of migratory preferences reflects the representation of various subsets within the intrahepatic lymphocytes surprisingly well, suggesting that the composition of intrahepatic lymphocytes is largely shaped by the dynamics of entry and exit of cells into the organ.

Immunomodulatory effects of the liver: deletion of activated CD4+ effector cells and suppression of IFN-gamma-producing cells after intravenous protein immunization.

The liver is tolerogenic in many situations, including as an allograft and during the response to allogeneic MHC expressed on hepatocytes. The majority of data that address this issue focus on endogenous Ags. Little is known about CD4(+) T cells and their fate under tolerizing conditions, especially with respect to fully differentiated CD4(+) effector T cells. In this study, we used the adoptive transfer of populations of TCR-transgenic CD4(+) T cells, skewed toward the Th1 or Th2 phenotype, to test whether either apoptotic or immune deviation mechanisms apply to cytokine-producing CD4(+) T cells that enter the liver. After transfer, Th1 and Th2 cells could be detected up to 25 days in lymphoid organs and the liver. Intravenous high dose Ag application resulted in accumulation, proliferation, and subsequent deletion of effector cells within the liver. Th1 cells lost their capacity to produce cytokines, whereas IL-4 expression was sustained within Th2 cells from the liver. However, there was no evidence for a deviation of Th1-programmed cells toward a Th2 (IL-4) or regulatory T cell (IL-10) pattern of cytokine expression. We used isolated populations of liver-derived APCs to test whether the liver had the capacity to impose a bias toward IL-4 expression in T cells. These experiments showed that liver sinusoidal endothelial cells selectively suppress the expansion of IFN-gamma-producing cells, yet they promote the outgrowth of IL-4-expressing Th2 cells, creating an immune suppressive milieu within this organ. These data suggest that presentation of Ags in the liver leads to modulation of immune response in terms of quantity and quality.