Immune response to diphtheria toxin-mediated depletion complicates the use of the CD11c-DTR(tg) model for studies of bacterial gastrointestinal infections

Repopulating Kupffer cells originate directly from hematopoietic stem cells

BACKGROUND

Kupffer cells (KCs) originate from yolk-sac progenitors before birth. Throughout adulthood, they self-maintain independently from the input of circulating monocytes (MOs) at a steady state and are replenished within 2 weeks after having been depleted, but the origin of repopulating KCs in adults remains unclear. The current paradigm dictates that repopulating KCs originate from preexisting KCs or monocytes, but there remains a lack of fate-mapping evidence.

METHODS

We first traced the fate of preexisting KCs and that of monocytic cells with tissue-resident macrophage-specific and monocytic cell-specific fate-mapping mouse models, respectively. Secondly, we performed genetic lineage tracing to determine the type of progenitor cells involved in response to KC-depletion in mice. Finally, we traced the fate of hematopoietic stem cells (HSCs) in an HSC-specific fate-mapping mouse model, in the context of chronic liver inflammation induced by repeated carbon tetrachloride treatment.

RESULTS

By using fate-mapping mouse models, we found no evidence that repopulating KCs originate from preexisting KCs or MOs and found that in response to KC-depletion, HSCs proliferated in the bone marrow, mobilized into the blood, adoptively transferred into the liver and differentiated into KCs. Then, in the chronic liver inflammation context, we confirmed that repopulating KCs originated directly from HSCs.

CONCLUSION

Taken together, these findings provided in vivo fate-mapping evidence that repopulating KCs originate directly from HSCs, which presents a completely novel understanding of the cellular origin of repopulating KCs and shedding light on the divergent roles of KCs in liver homeostasis and diseases.

Depletion of langerin+ cells enhances cutaneous wound healing

Langerin is a C-type lectin receptor that is expressed on Langerhans cells and langerin-positive dermal dendritic cells in the skin. Little is known about the function of langerin⁺ cells in wound healing. In this study, the effects of ablation of langerin⁺ cells on healing of a full-thickness excision wound were investigated using the langerin-DTR depletable mouse. Strikingly, depletion of langerin⁺ cells resulted in more rapid reduction in wound area. Accelerated wound healing in the langerin⁺ -cell-depleted group was characterized by enhanced neo-epidermis and granulation tissue formation, and increased cellular proliferation within the newly formed tissues. Accelerated healing in the absence of langerin⁺ cells was associated with increased levels of granulocyte-macrophage colony-stimulating factor, F4/80⁺ cells and blood vessels within the granulation tissue. These data support an inhibitory role for langerin⁺ cells during wound healing. Therapies that suppress langerin⁺ cells or their function may therefore have utility in progressing the healing of wounds in humans.

Suppression of CD4+ Effector Responses by Naturally Occurring CD4+ CD25+ Foxp3+ Regulatory T Cells Contributes to Experimental Cerebral Malaria

The role of naturally occurring CD4(+) CD25(+) Foxp3(+) regulatory T cells (nTreg) in the pathogenesis of cerebral malaria (CM), which involves both pathogenic T cell responses and parasite sequestration in the brain, is still unclear. To assess the contribution and dynamics of nTreg during the neuropathogenesis, we unbalanced the ratio between nTreg and naive CD4(+) T cells in an attenuated model of Plasmodium berghei ANKA-induced experimental CM (ECM) by using a selective cell enrichment strategy. We found that nTreg adoptive transfer accelerated the onset and increased the severity of CM in syngeneic C57BL/6 (B6) P. berghei ANKA-infected mice without affecting the level of parasitemia. In contrast, naive CD4(+) T cell enrichment prevented CM and promoted parasite clearance. Furthermore, early during the infection nTreg expanded in the spleen but did not efficiently migrate to the site of neuroinflammation, suggesting that nTreg exert their pathogenic action early in the spleen by suppressing the protective naive CD4(+) T cell response to P. berghei ANKA infection in vivo in both CM-susceptible (B6) and CM-resistant (B6-CD4(-/-)) mice. However, their sole transfer was not sufficient to restore CM susceptibility in two CM-resistant congenic strains tested. Altogether, these results demonstrate that nTreg are activated and functional during P. berghei ANKA infection and that they contribute to the pathogenesis of CM. They further suggest that nTreg may represent an early target for the modulation of the immune response to malaria.

Sampling of Candida albicans and Candida tropicalis by Langerin-positive dendritic cells in mouse Peyer's patches

Members of the Candida genus, including C. albicans and C. tropicalis are opportunistic fungal pathogens that are increasingly associated with gastrointestinal infections and inflammatory bowel diseases. In healthy populations, however, C. albicans and C. tropicalis are considered benign members of the mycobiome, and are presumably kept in check by the mucosal immune system. In this study, we demonstrate in mice that C. albicans and C. tropicalis are sampled by Peyer's patch (PP) dendritic cells (DCs). Uptake into gut-associated lymphoid tissues occurred rapidly and was at least partly M cell-dependent. C. albicans and C. tropicalis preferentially localized in (and persisted within) a recently identified sub- population of Peyer's patch DCs distinguished by their expression of the C-type lectin receptor, Langerin. This study is the first to identify a subset of PP DCs capable of sampling Candida species.

Yersinia pseudotuberculosis efficiently escapes polymorphonuclear neutrophils during early infection

The human-pathogenic species of the Gram-negative genus Yersinia preferentially target and inactivate cells of the innate immune defense, suggesting that this is a critical step by which these bacteria avoid elimination and cause disease. In this study, bacterial interactions with dendritic cells, macrophages, and polymorphonuclear neutrophils (PMNs) in intestinal lymphoid tissues during early Yersinia pseudotuberculosis infection were analyzed. Wild-type bacteria were shown to interact mainly with dendritic cells, but not with PMNs, on day 1 postinfection, while avirulent yopH and yopE mutants interacted with PMNs as well as with dendritic cells. To unravel the role of PMNs during the early phase of infection, we depleted mice of PMNs by using an anti-Ly6G antibody, after which we could see more-efficient initial colonization by the wild-type strain as well as by yopH, yopE, and yopK mutants on day 1 postinfection. Dissemination of yopH, yopE, and yopK mutants from the intestinal compartments to mesenteric lymph nodes was faster in PMN-depleted mice than in undepleted mice, emphasizing the importance of effective targeting of PMNs by these Yersinia outer proteins (Yops). In conclusion, escape from interaction with PMNs due to the action of YopH, YopE, and YopK is a key feature of pathogenic Yersinia species that allows colonization and effective dissemination.

Dendritic cells play a role in host susceptibility to Cryptosporidium parvum infection

Our previous studies have described dendritic cells (DCs) to be important sources of Th1 cytokines such as IL-12 and IL-2 in vitro, following stimulation with Cryptosporidium parvum antigens. We further established the role of DCs during cryptosporidiosis using a diphtheria toxin promoter regulated transgenic CD11c-DTR/EGFP mouse model. In vivo depletion of CD11c(+) cells in CD11c-DTR-Tg mice significantly increased susceptibility to C. parvum infection. Adoptive transfer of unstimulated or antigen stimulated DCs into CD11c(+) depleted CD11c-DTR-Tg mice resulted in an early decrease in parasite load at 4 days post infection. However, this response was transient since parasite load increased in mice engrafted with either unstimulated DCs or DCs stimulated with solubilized antigen by 6 days post infection. In contrast, in mice engrafted with DCs stimulated with live sporozoites, parasite load remained low during the entire period, suggesting the development of a more effective and sustained response. A corresponding increase in IFN-γ expression in T cells from spleen and mesenteric lymph nodes was also noted. Consistent with the in vivo engraftment study, DCs that are pulsed with live sporozoites in vitro and co-cultured with CD4(+) and CD8(+) T cells produced higher IFN-γ levels. Our study establishes the importance of DCs in susceptibility to infection by C. parvum and as important mediators of immune responses.

Adjuvant effect of diphtheria toxin after mucosal administration in both wild type and diphtheria toxin receptor engineered mouse strains

The finding that murine and simian cells have differential susceptibility to diphtheria toxin (DTx) led to the development of genetically engineered mouse strains that express the simian or human diphtheria toxin receptor (DTR) under the control of various mouse gene promoters. Injection of DTx into DTR engineered mice allows for rapid and transient depletion of various cell populations. There are several advantages to this approach over global knockout mice, including normal mouse development and temporal control over when cell depletion occurs. As a result, many DTR engineered mouse strains have been developed, resulting in significant insights into the cell biology of various disease states. We used Foxp3(DTR) mice to attempt local depletion of Foxp3+ cells in the lung in a model of tolerance breakdown. Intratracheal administration of DTx resulted in robust depletion of lung Foxp3+ cells. However, DTx administration was accompanied by significant local inflammation, even in control C57Bl/6 mice. These data suggest that DTx administration to non-transgenic mice is not always an immunologically inert event, and proper controls must be used to assess various DTx-mediated depletion regimens.

Dendritic cells and liver fibrosis

Dendritic cells are a relative rare population of specialized antigen presenting cells that are distributed through most lymphoid and non-lymphoid tissues and play a critical role in linking the innate and adaptive arms of the immune system. The liver contains a heterogeneous population of dendritic cells that may contribute to liver inflammation and fibrosis through a number of mechanisms. This review summarizes current knowledge on the development and characterization of liver dendritic cells and their potential impact on liver fibrosis. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.