Leishmania promastigotes evade interleukin 12 (IL-12) induction by macrophages and stimulate a broad range of cytokines from CD4+ T cells during initiation of infection.

Leishmania major are intramacrophage parasites whose eradication requires the induction of T helper 1 (Th1) effector cells capable of activating macrophages to a microbicidal state. Interleukin 12 (IL-12) has been recently identified as a macrophage-derived cytokine capable of mediating Th1 effector cell development, and of markedly enhancing interferon gamma (IFN-gamma) production by T cells and natural killer cells. Infection of macrophages in vitro by promastigotes of L. major caused no induction of IL-12 p40 transcripts, whereas stimulation using heat-killed Listeria or bacterial lipopolysaccharide induced readily detectable IL-12 mRNA. Using a competitor construct to quantitate a number of transcripts, a kinetic analysis of cytokine induction during the first few days of infection by L. major was performed. All strains of mice examined, including susceptible BALB/c and resistant C57BL/6, B10.D2, and C3H/HeN, had the appearance of a CD4+ population in the draining lymph nodes that contained transcripts for IL-2, IL-4, and IFN-gamma (and in some cases, IL-10) that peaked 4 d after infection. In resistant mice, the transcripts for IL-2, IL-4, and IL-10 were subsequently downregulated, whereas in susceptible BALB/c mice, these transcripts were only slightly decreased, and IL-4 continued to be reexpressed at high levels. IL-12 transcripts were first detected in vivo by 7 d after infection, consistent with induction by intracellular amastigotes. Challenge of macrophages in vitro confirmed that amastigotes, in contrast to promastigotes, induced IL-12 p40 mRNA. Reexamination of the cytokine mRNA at 4 d revealed expression of IL-13 in all strains analyzed, suggesting that IL-2 and IL-13 may mediate the IL-12-independent production of IFN-gamma during the first days after infection. Leishmania have evolved to avoid inducing IL-12 from host macrophages during transmission from the insect vector, and cause a striking induction of mRNAs for IL-2, IL-4, IL-10, and IL-13 in CD4+ T cells. Each of these activities may favor survival of the organism

ILC2s chew the fat.

In this issue of JEM, Rana et al. (https://doi.org/10.1084/jem.20190689) report that adipose tissue multipotent stromal cells (MSCs) provide multifaceted support for adipose tissue-resident ILC2s through contact-mediated proliferation and IL-33-mediated stress-induced activation

Cure of murine leishmaniasis with anti-interleukin 4 monoclonal antibody. Evidence for a T cell-dependent, interferon gamma-independent mechanism.

BALB/c mice infected with Leishmania major develop fatal, progressive disease, despite an immune response characterized by expansion of CD4+ T cells in the draining lymph nodes. The immune response has been further characterized by a lack of IFN-gamma mRNA, but increased IL-4 mRNA in lymphoid tissues, and striking elevation of serum IgE. Treatment of infected BALB/c mice with rIFN-gamma at doses shown to be beneficial in other protozoan infections was insufficient to ameliorate L. major infection. In contrast, neutralization of IL-4 by six weekly injections of mAb 11B11 led to attenuation of disease in 100% of animals, and complete cure in 85%. Resolution of disease required the presence of T cells, and recovered mice remained resistant to reinfection at 12 wk. This immunity was adoptively transferable and was dependent on both CD4+ and CD8+ cells. Although administration of anti-IL-4 was associated with fourfold increase in IFN-gamma mRNA in lymph node cells draining the lesion, the coadministration of neutralizing R4 6A2 anti-IFN-gamma mAb had no effect on resistance to disease. This was in marked contrast to resolution of disease in both resistant C57BL/6- and GK1.5-pretreated BALB/c mice that was abrogated by in vivo treatment with anti-IFN-gamma. These data suggest a novel mechanism of cellular immunity established by interference with the development of Th2 cells during infection

Human placental cytotrophoblasts produce the immunosuppressive cytokine interleukin 10.

The mechanism by which the mammalian mother accepts the implanting fetus as an allograft remains unexplained, but is likely to be the result of a combination of factors. Mononuclear cytotrophoblasts, the specialized fetal cells of the placenta that invade the uterus, play an important role. These cells express HLA-G, an unusual major histocompatibility complex class I-B molecule, and secrete cytokines and pregnancy-specific proteins that can regulate immune function. We investigated whether cytotrophoblasts secrete interleukin 10 (IL-10), a cytokine that potently inhibits alloresponses in mixed lymphocyte reactions. Cytotrophoblasts from all stages of pregnancy produced IL-10 in vitro, but neither placental fibroblasts nor choriocarcinoma (malignant trophoblast) cell lines did so. Spontaneous IL-10 production averaged 650, 853, and 992 pg/10(6) cells in the first, second, and third trimesters of pregnancy, respectively. IL-10 secretion dropped approximately 10-fold after the first 24 h of culture, and was paralleled by a decrease in messenger RNA. IL-10 messenger RNA was detected in biopsies of the placenta and the portion of the uterus that contains invasive cytotrophoblasts, suggesting that this cytokine is also produced in vivo. IL-10 secreted by cytotrophoblasts in vitro is bioactive, as determined by its ability to suppress interferon gamma production in an allogeneic mixed lymphocyte reaction. We conclude that human cytotrophoblast IL-10 may be an important factor that contributes to maternal tolerance of the allogeneic fetus

Interleukin 4, but not interleukin 5 or eosinophils, is required in a murine model of acute airway hyperreactivity.

Reversible airway hyperreactivity underlies the pathophysiology of asthma, yet the precise mediators of the response remain unclear. Human studies have correlated aberrant activation of T helper (Th) 2-like effector systems in the airways with disease. A murine model of airway hyperreactivity in response to acetylcholine was established using mice immunized with ovalbumin and challenged with aerosolized antigen. No airway hyperractivity occurred in severe combined immunodeficient mice. Identically immunized BALB/c mice developed an influx of cells, with a predominance of eosinophils and CD4+ T cells, into the lungs and bronchoalveolar lavage fluid at the time that substantial changes in airway pressure and resistance were quantitated. Challenged animals developed marked increases in Th2 cytokine production, eosinophil influx, and serum immunoglobulin E levels. Neutralization of interleukin (IL) 4 using monoclonal antibodies administered during the period of systemic immunization abrogated airway hyperractivity but had little effect on the influx of eosinophils. Administration of anti-IL-4 only during the period of the aerosol challenge did not affect the subsequent response to acetylcholine. Finally, administration of anti-IL-5 antibodies at levels that suppressed eosinophils to < 1% of recruited cells had no effect on the subsequent airway responses. BALB/c mice had significantly greater airway responses than C57BL/6 mice, consistent with enhanced IL-4 responses to antigen in BALB/c mice. Taken together, these data implicate IL-4 generated during the period of lymphocyte priming with antigen in establishing the cascade of responses required to generate airway hyperractivity to inhaled antigen. No role for IL-5 or eosinophils could be demonstrated

Reciprocal expression of interferon gamma or interleukin 4 during the resolution or progression of murine leishmaniasis. Evidence for expansion of distinct helper T cell subsets.

We purified poly(A)+ mRNA from the spleen and lymph nodes at designated times after infection with Leishmania major in genetically susceptible BALB/c and resistant C57BL/6 mice. The steady-state levels of IL-2, IFN-gamma, IL-4, and IL-1 beta mRNA were determined using Northern hybridizations. IL-2 mRNA levels in the infected organs of BALB/c and C57BL/6 mice were comparable after infection, but IFN-gamma and IL-4 mRNA levels were reciprocally expressed. Levels of IFN-gamma mRNA in C57BL/6 draining nodes and spleen were significantly greater than in BALB/c mice except at 4 and 6 wk of infection, when splenic IFN-gamma mRNA levels were transiently comparable. In contrast, IL-4 mRNA was apparent only in BALB/c and not in C57BL/6 nodes and spleen. Tissue levels of IL-1 beta mRNA were 10-20-fold greater in BALB/c mice. BALB/c mice were pretreated with GK1.5 mAb, a manipulation that promotes healing of subsequent infection by transiently depleting L3T4+ cells. At 8 wk of infection, by which time lymphoid organs were repopulated with L3T4+ cells, GK1.5-pretreated BALB/c mice produced IFN-gamma, but not IL-4 message. Serum levels of IgE were markedly elevated in infected BALB/c, but not in infected C57BL/6 or GK1.5-pretreated BALB/c mice, consistent with in vivo biologic activity of IL-4 in nonhealing mice. Treatment of infected BALB/c mice with neutralizing anti-IL-4 antibody abolished the elevation of serum IgE and significantly attenuated the progression of disease as assessed by size and ulceration of the lesion, and by reduction in the number of tissue parasites. Both protective and deleterious responses to Leishmania infection have previously been shown to be L3T4+ cell dependent. Our findings are consistent with the differential expansion of protective, IFN-gamma-producing Th1 cells in healing mice, and the expansion of deleterious, IL-4-producing Th2 cells in nonhealing mice. The inverse relationship of IFN-gamma and IL-4 gene expression during leishmaniasis may underlie the divergence of cellular and humoral immunity that occurs during chronic infection with Leishmania and possibly other intracellular parasites

Leukotrienes provide an NFAT-dependent signal that synergizes with IL-33 to activate ILC2s.

Group 2 innate lymphoid cells (ILC2s) and type 2 helper T cells (Th2 cells) are the primary source of interleukin 5 (IL-5) and IL-13 during type 2 (allergic) inflammation in the lung. In Th2 cells, T cell receptor (TCR) signaling activates the transcription factors nuclear factor of activated T cells (NFAT), nuclear factor κB (NF-κB), and activator protein 1 (AP-1) to induce type 2 cytokines. ILC2s lack a TCR and respond instead to locally produced cytokines such as IL-33. Although IL-33 induces AP-1 and NF-κB, NFAT signaling has not been described in ILC2s. In this study, we report a nonredundant NFAT-dependent role for lipid-derived leukotrienes (LTs) in the activation of lung ILC2s. Using cytokine reporter and LT-deficient mice, we find that complete disruption of LT signaling markedly diminishes ILC2 activation and downstream responses during type 2 inflammation. Type 2 responses are equivalently attenuated in IL-33- and LT-deficient mice, and optimal ILC2 activation reflects potent synergy between these pathways. These findings expand our understanding of ILC2 regulation and may have important implications for the treatment of airways disease

MicroRNA regulation of type 2 innate lymphoid cell homeostasis and function in allergic inflammation.

MicroRNAs (miRNAs) exert powerful effects on immunity through coordinate regulation of multiple target genes in a wide variety of cells. Type 2 innate lymphoid cells (ILC2s) are tissue sentinel mediators of allergic inflammation. We established the physiological requirements for miRNAs in ILC2 homeostasis and immune function and compared the global miRNA repertoire of resting and activated ILC2s and T helper type 2 (TH2) cells. After exposure to the natural allergen papain, mice selectively lacking the miR-17∼92 cluster in ILC2s displayed reduced lung inflammation. Moreover, miR-17∼92-deficient ILC2s exhibited defective growth and cytokine expression in response to IL-33 and thymic stromal lymphopoietin in vitro. The miR-17∼92 cluster member miR-19a promoted IL-13 and IL-5 production and inhibited expression of several targets, including SOCS1 and A20, signaling inhibitors that limit IL-13 and IL-5 production. These findings establish miRNAs as important regulators of ILC2 biology, reveal overlapping but nonidentical miRNA-regulated gene expression networks in ILC2s and TH2 cells, and reinforce the therapeutic potential of targeting miR-19 to alleviate pathogenic allergic responses

Tissue signals imprint ILC2 identity with anticipatory function.

Group 2 innate lymphoid cells (ILC2s) are distributed systemically and produce type 2 cytokines in response to a variety of stimuli, including the epithelial cytokines interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin (TSLP). Transcriptional profiling of ILC2s from different tissues, however, grouped ILC2s according to their tissue of origin, even in the setting of combined IL-25-, IL-33-receptor-, and TSLP-receptor-deficiency. Single-cell profiling confirmed a tissue-organizing transcriptome and identified ILC2 subsets expressing distinct activating receptors, including the major subset of skin ILC2s, which were activated preferentially by IL-18. Tissue ILC2 subsets were unaltered in number and expression in germ-free mice, suggesting that endogenous, tissue-derived signals drive the maturation of ILC2 subsets by controlling expression of distinct patterns of activating receptors, thus anticipating tissue-specific perturbations occurring later in life

Parasitic helminths induce fetal-like reversion in the intestinal stem cell niche.

Epithelial surfaces form critical barriers to the outside world and are continuously renewed by adult stem cells1. Whereas dynamics of epithelial stem cells during homeostasis are increasingly well understood, how stem cells are redirected from a tissue-maintenance program to initiate repair after injury remains unclear. Here we examined infection by Heligmosomoides polygyrus, a co-evolved pathosymbiont of mice, to assess the epithelial response to disruption of the mucosal barrier. H. polygyrus disrupts tissue integrity by penetrating the duodenal mucosa, where it develops while surrounded by a multicellular granulomatous infiltrate2. Crypts overlying larvae-associated granulomas did not express intestinal stem cell markers, including Lgr53, in spite of continued epithelial proliferation. Granuloma-associated Lgr5- crypt epithelium activated an interferon-gamma (IFN-γ)-dependent transcriptional program, highlighted by Sca-1 expression, and IFN-γ-producing immune cells were found in granulomas. A similar epithelial response accompanied systemic activation of immune cells, intestinal irradiation, or ablation of Lgr5+ intestinal stem cells. When cultured in vitro, granuloma-associated crypt cells formed spheroids similar to those formed by fetal epithelium, and a sub-population of H. polygyrus-induced cells activated a fetal-like transcriptional program, demonstrating that adult intestinal tissues can repurpose aspects of fetal development. Therefore, re-initiation of the developmental program represents a fundamental mechanism by which the intestinal crypt can remodel itself to sustain function after injury