Characterization of the stage in natural killer cell development in 14.5-day mouse fetal liver using adult bone marrow stroma

Murine hepatocyte cell lines promote expansion and differentiation of NK cells from stem cell precursors

While fetal liver is a major hematopoietic organ, normal adult liver provides a suitable microenvironment for a variety of immune cells and, in several pathological conditions, may become a site of extramedullary hematopoiesis. The direct influence of hepatocytes on hematopoietic cell differentiation is poorly understood. We have previously reported that the Met murine hepatocyte (MMH) untransformed hepatocytic lines retain several morphological and functional features of hepatocytes in vivo and are able to support the survival, self-renewal, and differentiation of hematopoietic precursors in a cell-cell contact system. Here we report the effects of soluble factors released by MMH lines on bone marrow-derived cells. Lymphohematopoietic cells were cultured in two different cell contact-free systems: transwell inserts on MMH feeder layers, and MMH conditioned medium (MMH-CM). Both culture systems were able to promote a substantial expansion of bone marrow-derived cells and their differentiation to natural killer (NK) cells that express the NK1.1 and U5A2-13 markers. Purified hematopoietic stem cells (Sca-1+Lin-), either plated as a bulk population or as single cells, were also able to differentiate into NK cells, when cultured in MMH-CM; thus, soluble factors secreted by MMH lines promote the expansion and differentiation of NK precursor cells. MMH-CM-derived NK cells are functionally active; stimulation by interleukin (IL)-12 together with IL-18 was required to induce interferon-gamma (IFNgamma) expression and to enhance their cytotoxic activity. In conclusion, our findings may imply a direct role of hepatocytes in NK cell development, and the system we have used may provide a tool for studying the molecular mechanisms of NK cell differentiation.

Neither lymphotoxin alpha nor lymphotoxin beta receptor expression is required for biogenesis of lymphoid aggregates or differentiation of natural killer cells in the pregnant mouse uterus

Gene ablation studies in mice indicate that lymphotoxin (LT)alpha, LTbeta and LTbetaR are essential for the genesis of lymph nodes (LN), normal structural development of peripheral lymphoid tissues and the differentiation of natural killer (NK) cells. LTbetaR binds to the heterotrimeric cytokines LTalpha1beta2 and LIGHT. LTs also regulate stromal cell expression of lymphocyte homing chemokines. Uterine decidualization in normal (+/+) mice is accompanied by the appearance and maturation of large numbers of uterine NK (uNK) cells that differentiate from precursors mobilized to the uterus from secondary lymphoid tissues. uNK cells accumulate in a transient, lymphocyte-rich region known as the metrial gland or, more recently, the mesometrial lymphoid aggregrate of pregnancy (MLAp). To determine if LTs contribute to development of the MLAp, and to the differentiation and/or localization of uNK cells, a histological study was undertaken of implantation sites from LTalpha null, LTbetaR null and gestation day-matched, normal mice. Implantation sites from the gene-ablated mice contained abundant numbers of uNK cells that localized appropriately. This indicates that the stromally derived molecules supporting NK cell differentiation in the uterus differ from those used in secondary lymphoid organs.

Murine leptin deficiency alters Kupffer cell production of cytokines that regulate the innate immune system

BACKGROUND & AIMS

ob/ob mice are used to study the mechanisms that regulate the progression from steatosis to nonalcoholic steatohepatitis. The livers of ob/ob mice are depleted of CD4-positive natural killer cells, components of the innate immune system that induce anti-inflammatory cytokines. Although this may explain the sensitivity of fatty livers to lipopolysaccharide, why such hepatic CD4-positive natural killer cell depletion occurs is uncertain. Because leptin regulates macrophages, our hypothesis is that leptin deficiency alters Kupffer cell production of cytokines that inhibit (e.g., interleukin [IL]-12) or enhance (e.g., IL-15) hepatic CD4-positive natural killer cell viability.

METHODS

Kupffer cell cytokine production and the hepatic content of CD4-positive natural killer cells were compared in ob/ob and lean mice. ob/ob mice were then treated with IL-15 or leptin to determine whether either factor improved their immunologic abnormalities.

RESULTS

Compared with control Kupffer cells, ob/ob Kupffer cells produced less IL-15 basally and more IL-12 after lipopolysaccharide stimulation. Treatment of ob/ob mice with IL-15 for 1 week normalizes their hepatic CD4-positive natural killer cell content. Leptin increases the hepatic expression of IL-15 in ob/ob mice and partially replenishes their hepatic CD4-positive natural killer cells.

CONCLUSIONS

Leptin deficiency increases hepatic IL-12 and reduces hepatic IL-15 expression. The abnormal production of these Kupffer cell factors promotes hepatic CD4-positive natural killer cell depletion in ob/ob livers.

Alloreactivity following in utero transplantation of cytokine-stimulated hematopoietic stem cells: the role of recipient CD4(-) cells

OBJECTIVE

We have previously reported immunity to donor antigens following in utero transplantation (IUT) of cytokine-stimulated allogeneic hematopoietic stem cells (sca(+)/lin(-)) (day 9 of gestation). Transplanted mice showed accelerated rejection of donor skin grafts and high anti-donor cytotoxic response, a finding not seen in the control mice. This was accompanied by an enhancement of Th1 over Th2 cytokine production and persistent donor microchimerism. In order to assess the role of the thymus in allograft rejection, prenatal transplants were performed under similar experimental conditions at a later gestational age, when the thymus is more developed (day 13).

MATERIALS AND METHODS

Cytokine-stimulated stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF)-purified sca(+)/lin(-) cells of C57BL/6 (H-2b, 1E(+)) background were injected into MHC-mismatched BALB/c (H-2d, 1E(-)) fetal mouse recipients at day 13 of gestation. Chimerism was determined by highly sensitive (0.001%) semiquantitative polymerase chain reaction (PCR). Mixed lymphocyte reaction (MLR) and cytotoxic T-cell assay (CTL) were used to evaluate tolerance vs immunity. Cytokine levels were quantified in MLR supernatants using ELISA assay. The percent of T cells was determined by flow cytometry (FACS) and CD4/CD8 ratio calculated. Postnatal boosts (transplants without conditioning) were performed at 6 months of age to enhance donor chimerism and test the degree of tolerance.

RESULTS

When assayed at 4 months of age, donor-type cells were not detected in the spleen or in the peripheral blood of BALB/c mice inoculated with C57BL/6 sca(+)/lin(-) cells. Transplanted but not control animals demonstrated high anti-donor MLR but not CTL responses. The increase of MLR reactivity was correlated with high levels of IL-2. Furthermore, transplanted mice showed higher resistance to postnatal boosts with allogeneic bone marrow (BM) cells, when compared to the control mice. The later resistance was accompanied by the expansion of host-type CD4 cells.

CONCLUSION

These data demonstrate that transplantation of cytokine-stimulated sca(+)/lin(-) allogeneic cells at 13 days of fetal development leads to the allosensitization, characterized by an enhancement of MLR alloreactivity and by the rejection of postnatal boosts (transplants without conditioning). Host-type CD4 cells might play a central role in this rejection. These findings indicate that the late injection of allogeneic cells may result in the development of allosensitization with subsequent donor graft rejection. Precise conditions for the development of tolerance must be established before prenatal transplants in humans with conditions other than SCID can be done.

Onset of natural killer cell lymphomas in transgenic mice carrying a truncated HMGI-C gene by the chronic stimulation of the IL-2 and IL-15 pathway

Rearrangements of the high mobility group protein I-C (HMGI-C) gene, consisting in the loss of the carboxyl-terminal tail, have been frequently detected in benign human tumors of mesenchymal origin. We have previously demonstrated that transgenic (TG) mice carrying a truncated HMGI-C construct (HMGI-C/T) exhibit a giant phenotype together with a predominantly abdominal/pelvic lipomatosis. Here, we report that HMGI-C/T TG mice develop natural killer (NK)-T/NK cell lymphomas starting from 12 months of age. We found an increased expression of IL-2 and IL-15 proteins and their receptors in these lymphomas, and we demonstrate that HMGI-C/T protein positively regulates their expression in vitro. Therefore, the HMGI-C/T-mediated chronic stimulation of the IL-2/IL-15 pathway could be responsible for the onset of NK-T/NK cell lymphomas in HMGI-C/T TG mice.

Signal via lymphotoxin-beta R on bone marrow stromal cells is required for an early checkpoint of NK cell development

NK cells play an important role in the immune system but the cellular and molecular requirements for their early development are poorly understood. Lymphotoxin-alpha (LTalpha)(-/-) and LTbetaR(-/-) mice show a severe systemic reduction of NK cells, which provides an excellent model to study NK cell development. In this study, we show that the bone marrow (BM) or fetal liver cells from LTalpha(-/-) or LTbetaR(-/-) mice efficiently develop into mature NK cells in the presence of stromal cells from wild-type mice but not from LTalpha(-/-) or LTbetaR(-/-) mice. Direct activation of LTbetaR-expressing BM stromal cells is shown to promote to early NK cell development in vitro. Furthermore, the blockade of the interaction between LT and LTbetaR in adult wild-type mice by administration of LTbetaR-Ig impairs the development of NK cells in vivo. Together, these results indicate that the signal via LTbetaR on BM stromal cells by membrane LT is an important pathway for early NK cell development.