Sandrine I. Samson

Roles for Common Cytokine Receptor γ-Chain-Dependent Cytokines in the Generation, Differentiation, and Maturation of NK Cell Precursors and Peripheral NK Cells in Vivo

NK cells differentiate in adult mice from bone marrow hemopoietic progenitors. Cytokines, including those that signal via receptors using the common cytokine receptor γ-chain (γc), have been implicated at various stages of NK cell development. We have previously described committed NK cell precursors (NKPs), which have the capacity to generate NK cells, but not B, T, erythroid, or myeloid cells, after in vitro culture or transfer to a fetal thymic microenvironment. NKPs express the CD122 Ag (β chain of the receptors for IL-2/IL-15), but lack other mature NK markers, including NK1.1, CD49b (DX5), or members of the Ly49 gene family. In this report, we have analyzed the roles for γc-dependent cytokines in the generation of bone marrow NKP and in their subsequent differentiation to mature NK cells in vivo. Normal numbers of NKPs are found in γc-deficient mice, suggesting that NK cell commitment is not dependent on IL-2, IL-4, IL-7, IL-9, IL-15, or IL-21. Although IL-2, IL-4, and IL-7 have been reported to influence NK cell differentiation, we find that mice deficient in any or all of these cytokines have normal NK cell numbers, phenotype, and effector functions. In contrast, IL-15 plays a dominant role in early NK cell differentiation by maintaining normal numbers of immature and mature NK cells in the bone marrow and spleen. Surprisingly, the few residual NK cells generated in absence of IL-15 appear relatively mature, expressing a variety of Ly49 receptors and demonstrating lytic and cytokine production capacity.

GATA-3 Promotes Maturation, IFN-γ Production, and Liver-Specific Homing of NK Cells

The GATA-3 transcription factor has a determinant role in T cell specification and is an essential mediator of T helper 2-type polarized immune responses. While both committed NK precursors and mature NK cells express GATA-3, a role of this transcription factor in murine NK cell differentiation is not known. We found that NK cells, in contrast to T cells, can be generated in the absence of GATA-3. However, while GATA-3 antagonizes IFN-gamma production in differentiating T cells, GATA-3-deficient NK cells paradoxically produced less IFN-gamma compared to control NK cells and failed to provide early protection in vivo against infection with Listeria monocytogenes. Surprisingly, GATA-3 was essential for NK cell homing to the liver. Our results suggest that GATA-3 promotes NK cell maturation and acts in this lineage to specify distinct effector phenotypes.

Commensal bacteria trigger a full dendritic cell maturation program that promotes the expansion of non-Tr1 suppressor T cells

Dendritic cells (DCs) orchestrate the immune response establishing immunity versus tolerance. These two opposite functions may be dictated by DC maturation status with maturity linked to immunogenicity. DCs directly interact with trillions of noninvasive intestinal bacteria in vivo, a process that contributes to gut homeostasis. We here evaluated the maturation program elicited in human DCs by direct exposure to commensal‐related bacteria (CB) in the absence of inflammatory signals. We showed that eight gram+ and gram− CB strains up‐regulated costimulatory molecule expression in DCs and provoked a chemokine receptor switch similar to that activated by gram+ pathogens. CB strains may be classified into three groups according to DC cytokine release: high IL‐12 and low IL‐10; low IL‐12 and high IL‐10; and low IL‐12 and IL‐10. All CB‐treated DCs produced IL‐1β and IL‐6 and almost no TGF‐β. Yet, CB instructed DCs to convert naive CD4+ T cells into hyporesponsive T cells that secreted low or no IFN‐γ, IL‐10, and IL‐17 and instead, displayed suppressor function. These data demonstrate that phenotypic DC maturation combined to an appropriate cytokine profile is insufficient to warrant Th1, IL‐10‐secreting T regulatory Type 1 (Tr1), or Th17 polarization. We propose that commensal flora and as such, probiotics manipulate DCs by a yet‐unidentified pathway to enforce gut tolerance.

Lactic acid bacteria as adjuvants for sublingual allergy vaccines.

We compared immunomodulatory properties of 11 strains of lactic acid bacteria as well as their capacity to enhance sublingual immunotherapy efficacy in a murine asthma model. Two types of bacterial strains were identified, including: (i) potent inducers of IL-12p70 and IL-10 in dendritic cells, supporting IFN-gamma and IL-10 production in CD4+ T cells such as Lactobacillus helveticus; (ii) pure Th1 inducers such as L. casei. Sublingual administration in ovalbumin-sensitized mice of L. helveticus, but not L. casei, reduced airways hyperresponsiveness, bronchial inflammation and proliferation of specific T cells in cervical lymph nodes. Thus, probiotics acting as a Th1/possibly Treg, but not Th1 adjuvant, potentiate tolerance induction via the sublingual route.

IκBα/IκBε deficiency reveals that a critical NF-κB dosage is required for lymphocyte survival

In most cells, the NF-κB transcription factor is sequestered in the cytoplasm by interaction with inhibitory proteins, the IκBs. Here, we show that combined IκBα/IκBε deficiency in mice leads to neonatal death, elevated κB binding activity, overexpression of NF-κB target genes, and disruption of lymphocyte production. In IκBα/IκBε-deficient fetuses, B220+IgM+ B cells and single-positive T cells die by apoptosis. In adults, IκBα-/-IκBε-/- reconstituted chimeras exhibit a nearly complete absence of T and B cells that is not rescued by cotransfer with wild-type bone marrow. These findings demonstrate that IκBs tightly control NF-κB activity in vivo and that increased NF-κB activity intrinsically impairs lymphocyte survival. Because reduction or rise of NF-κB activity leads to similar dysfunction, they also reveal that only a narrow window of NF-κB activity is tolerated by lymphocytes.

Selected commensal-related bacteria and Toll-like receptor 3 agonist combinatorial codes synergistically induce interleukin-12 production by dendritic cells to trigger a T helper type 1 polarizing programme

Enteric infections remain a major health problem causing millions of deaths in developing countries. The interplay among the host intestinal epithelium, the mucosa‐associated immune system and microbiota performs an essential role in gut homeostasis and protection against infectious diseases. Dendritic cells (DCs) play a key role in orchestrating protective immunity and tolerance in the gut. The mechanisms by which DCs adapt their responses and discriminate between virulent microbes and trillions of innocuous bacteria remain ill‐defined. Here we investigated the effect of cross‐talk between commensal‐related bacteria (CB) and Toll‐like receptor (TLR) agonists on DC activation and the outcome of the in vitro T helper response. Human monocyte‐derived DCs were exposed to eight different Gram‐positive or Gram‐negative CB strains prior to activation with five different TLR agonists. The key polarizing cytokines interleukin (IL)‐12p70, IL‐10, IL‐1β and IL‐6 were quantified and the fate of naïve T‐cell differentiation was evaluated. We identified a unique combination of Lactobacillus casei and TLR3 signals that acted in synergy to selectively increase IL‐12p70 secretion. Exposure to poly(I:C) converted L. casei‐treated DCs into potent promoters of T helper type 1 (Th1) responses. We propose that DCs can integrate harmless and dangerous non‐self signals delivered by viral products, to mount robust Th1 responses. Thus, in vivo DC targeting with selective probiotics may improve strategies for the management of enteric diseases.