Natural killer (NK) and NK T cells are tissue lymphocytes that secrete cytokines rapidly upon stimulation. Here, we show that these cells maintain distinct patterns of constitutive cytokine mRNAs. Unlike conventional T cells, NK T cells activate interleukin (IL)-4 and interferon (IFN)-gamma transcription during thymic development and populate the periphery with both cytokine loci previously modified by histone acetylation. Similarly, NK cells transcribe and modify the IFN-gamma gene, but not IL-4, during developmental maturation in the bone marrow. Lineage-specific patterns of cytokine transcripts predate infection and suggest evolutionary selection for invariant but distinct types of effector responses among the earliest responding lymphocytes.

The relationship of T follicular helper (TFH) cells to other T helper (Th) subsets is controversial. We find that after helminth infection, or immunization with helminth antigens, reactive lymphoid organs of 4get IL-4/GFP reporter mice contain populations of IL-4/GFP-expressing CD4(+) T cells that display the TFH markers CXCR5, PD-1, and ICOS. These TFH cells express the canonical TFH markers BCL6 and IL-21, but also GATA3, the master regulator of Th2 cell differentiation. Consistent with a relationship between Th2 and TFH cells, IL-4 protein production, reported by expression of huCD2 in IL-4 dual reporter (4get/KN2) mice, was a robust marker of TFH cells in LNs responding to helminth antigens. Moreover, the majority of huCD2/IL-4-producing Th cells were found within B cell follicles, consistent with their definition as TFH cells. TFH cell development after immunization failed to occur in mice lacking B cells or CD154. The relationship of TFH cells to the Th2 lineage was confirmed when TFH cells were found to develop from CXCR5(-) PD-1(-) IL-4/GFP(+) CD4(+) T cells after their transfer into naive mice and antigen challenge in vivo.

The liver is a common host organ for cancer, either through lesions that arise in liver epithelial cells [e.g., hepatocellular carcinoma (HCC)] or as a site of metastasis by tumors arising in other organs (e.g., colorectal cancer). However, the changes that occur in liver stromal cells in response to cancer have not been fully characterized, nor has it been determined whether the different sources of liver cancer induce distinct stromal changes. Here, we performed single-cell profiling of liver stromal cells from mouse models of induced spontaneous liver cancer or implanted colorectal liver metastases, with a focus on tumor endothelial cells (ECs). While ECs in liver tissue adjacent to cancerous lesions (so-called adjacent normal) corresponded to liver zonation phenotypes, their transcriptomes were also clearly altered by the presence of a tumor. In comparison, tumor EC transcriptomes show stronger similarities to venous than sinusoidal ECs. Further, tumor ECs, independent of tumor origin, formed distinct clusters displaying conserved "tip-like" or "stalk-like" characteristics, similar to ECs from subcutaneous tumors. However, they also carried liver-specific signatures found in normal liver ECs, suggesting an influence of the host organ on tumor ECs. Our results document gene expression signatures in ECs in liver cancer and show that the host organ, and not the site of tumor origin (liver versus colorectal), is a primary determinant of EC phenotype. In addition, primarily in tumors, we further defined a cluster of chimeric cells that expressed both myeloid and endothelial cell markers and might play a role in tumor angiogenesis.

Innate lymphoid cells (ILCs) are a heterogeneous family of immune regulators that protect against mucosal pathogens but can also promote intestinal pathology. Although the plasticity between ILCs populations has been described, the role of mucosal pathogens in inducing ILC conversion leading to intestinal pathology remains unclear. Here we demonstrate that IFNγ-producing ILCs are responsible for promoting intestinal pathology in a mouse model of enterocolitis caused by Campylobacter jejuni, a common human enteric pathogen. Phenotypic analysis revealed a distinct population of IFNγ-producing NK1.1-T-bet+ILCs that accumulated in the intestine of C. jejuni-infected mice. Adoptive transfer experiments demonstrated their capacity to promote intestinal pathology. Inactivation of T-bet in NKp46+ ILCs ameliorated disease. Transcriptome analysis and cell-fate mapping experiments revealed that IFNγ-producing NK1.1-ILCs correspond to ILC1 profile and develop from RORγt+ progenitors. Collectively, we identified a distinct population of NK1.1-ex-ILC3s that promotes intestinal pathology through IFNγ production in response to C. jejuni infection.

Interleukin (IL)-4 is the quintessential T helper type 2 (Th2) cytokine produced by CD4(+) T cells in response to helminth infection. IL-4 not only promotes the differentiation of Th2 cells but is also critical for immunoglobulin (Ig) G1 and IgE isotype-switched antibody responses. Despite the IL-4-mediated link between Th2 cells and B lymphocytes, the location of IL-4-producing T cells in the lymph nodes is currently unclear. Using IL-4 dual reporter mice, we examined the Th2 response and IL-4 production in the draining mesenteric lymph nodes during infection with the enteric nematode Heligmosomoides polygyrus. We show that although IL-4-competent Th2 cells are found throughout the B and T cell areas, IL-4-producing Th2 cells are restricted to the B cell follicles and associate with germinal centers. Consistent with their localization, IL-4 producers express high levels of CXCR5, ICOS, PD-1, IL-21, and BCL-6, a phenotype characteristic of T follicular helper (Tfh) cells. Although IL-4 was dispensable for the generation of Th2 and Tfh cells, its deletion resulted in defective B cell expansion and maturation. Our report reveals the compartmentalization of Th2 priming and IL-4 production in the lymph nodes during infection, and identifies Tfh cells as the dominant source of IL-4 in vivo.

Omega-1, a glycosylated T2 ribonuclease (RNase) secreted by Schistosoma mansoni eggs and abundantly present in soluble egg antigen, has recently been shown to condition dendritic cells (DCs) to prime Th2 responses. However, the molecular mechanisms underlying this effect remain unknown. We show in this study by site-directed mutagenesis of omega-1 that both the glycosylation and the RNase activity are essential to condition DCs for Th2 polarization. Mechanistically, we demonstrate that omega-1 is bound and internalized via its glycans by the mannose receptor (MR) and subsequently impairs protein synthesis by degrading both ribosomal and messenger RNA. These experiments reveal an unrecognized pathway involving MR and interference with protein synthesis that conditions DCs for Th2 priming.

The development of T cell memory from naive precursors is influenced by molecular cues received during T cell activation and differentiation. In this study, we describe a novel role for the chemokine receptors CCR5 and CXCR3 in regulating effector CD8(+) T cell contraction and memory generation after influenza virus infection. We find that Ccr5(-/-) Cxcr3(-/-) cells show markedly decreased contraction after viral clearance, leading to the establishment of massive numbers of memory CD8(+) T cells. Ccr5(-/-) Cxcr3(-/-) cells show reduced expression of CD69 in the lung during the peak of infection, which coincides with differential localization and the rapid appearance of memory precursor cells. Analysis of single chemokine receptor-deficient cells revealed that CXCR3 is primarily responsible for this phenotype, although there is also a role for CCR5 in the enhancement of T cell memory. The phenotype could be reversed by adding exogenous antigen, resulting in the activation and contraction of Ccr5(-/-) Cxcr3(-/-) cells. Similar results were observed during chronic Mycobacterium tuberculosis infection. Together, the data support a model of memory CD8(+) T cell generation in which the chemokine-directed localization of T cells within infected tissues regulates antigen encounter and controls the extent of CD8(+) T cell activation and differentiation, which ultimately regulates effector versus memory cell fate decisions.

Cytokines are soluble proteins that regulate immune responses. The present paradigm is that cytokine production in lymphoid tissues is tightly localized and signaling occurs between conjugate cells. Here we assess cytokine signaling during infection by measuring in vivo phosphorylation of intracellular signal transducer and activator of transcription (STAT) proteins. We show that interferon-gamma (IFN-gamma) and interleukin 4 (IL-4) signaled to the majority of lymphocytes throughout the reactive lymph node and that IL-4 conditioning of naive, bystander cells was sufficient to override opposing T helper type 1 (T(H)1) polarization. Our results demonstrate that despite localized production, cytokines can permeate a lymph node and modify the majority of cells therein. Cytokine conditioning of bystander cells could provide a mechanism by which chronic worm infections subvert the host response to subsequent infections or vaccination attempts.

Efficacy of immune checkpoint inhibitors in cancers can be limited by CD8 T cell dysfunction or HLA-I down-regulation. Tumor control mechanisms independent of CD8/HLA-I axis would overcome these limitations. Here, we report potent CD4 T cell-mediated tumor regression and memory responses in humanized immune system (HIS) mice implanted with HT-29 colorectal tumors. The regressing tumors showed increased CD4 cytotoxic T lymphocyte (CTL) infiltration and enhanced tumor HLA-II expression compared to progressing tumors. The intratumoral CD4 T cell subset associated with tumor regression expressed multiple cytotoxic markers and exhibited clonal expansion. Notably, tumor control was abrogated by depletion of CD4 but not CD8 T cells. CD4 T cells derived from tumor-regressing mice exhibited HLA-II-dependent and tumor-specific killing ex vivo. Taken together, our study demonstrates a critical role of human CD4 CTLs in mediating tumor clearance independent of CD8 T cells and provides a platform to study human anti-tumor immunity in vivo.

In schistosomiasis patients, parasite eggs trapped in hepatic sinusoids become foci for CD4+ T cell-orchestrated granulomatous cellular infiltrates. Since the immune response is unable to clear the infection, the liver is subjected to ongoing cycles of focal inflammation and healing that lead to vascular obstruction and tissue fibrosis. This is mitigated by regulatory mechanisms that develop over time and which minimize the inflammatory response to newly deposited eggs. Exploring changes in the hepatic inflammatory infiltrate over time in infected mice, we found an accumulation of schistosome egg antigen-specific IgG1-secreting plasma cells during chronic infection. This population was significantly diminished by blockade of the receptor for IL-10, a cytokine implicated in plasma cell development. Strikingly, IL-10R blockade precipitated the development of portal hypertension and the accumulation of parasite eggs in the lungs and heart. This did not reflect more aggressive Th2 cell responsiveness, increased hepatic fibrosis, or the emergence of Th1 or Th17 responses. Rather, a role for antibody in the prevention of severe disease was suggested by the finding that pulmonary involvement was also apparent in mice unable to secrete class switched antibody. A major effect of anti-IL-10R treatment was the loss of a myeloid population that stained positively for surface IgG1, and which exhibited characteristics of regulatory/anti-inflammatory macrophages. This finding suggests that antibody may promote protective effects within the liver through local interactions with macrophages. In summary, our data describe a role for IL-10-dependent B cell responses in the regulation of tissue damage during a chronic helminth infection.

Immunity to the intestinal parasite Heligomosomoides polygyrus is dependent on the successful generation of T helper 2 (Th2) memory cells. We showed that B cells contribute to immunity against H. polygyrus by producing antibody (Ab) and by promoting expansion and differentiation of primary and memory Th2 cells. We also demonstrated that cytokine-producing effector B cells were essential for effective immunity to H. polygyrus. Tumor necrosis factor alpha production by B cells was necessary for sustained Ab production, whereas interleukin 2 production by B cells was necessary for Th2 cell expansion and differentiation. These results show that B cells mediate protection from pathogens not only by presenting antigen and secreting antibody but also by producing cytokines that regulate the quality and magnitude of humoral and cellular immune responses.

Surviving infection represents a balance between the proinflammatory responses needed to eliminate the pathogen, and anti-inflammatory signals limiting damage to the host. IL-10 is a potent immunosuppressive cytokine whose impact is determined by the timing and localization of release. We show that NK cells rapidly express IL-10 during acute infection with diverse rapidly disseminating pathogens. The proinflammatory cytokine IL-12 was necessary and sufficient for NK cell induction of IL-10. NK cells from mice with systemic parasitic infection inhibited dendritic cell release of IL-12 in an IL-10-dependent manner, and NK cell depletion resulted in elevated serum IL-12. These data suggest an innate, negative feedback loop in which IL-12 limits its own production by eliciting IL-10 from NK cells. In contrast to disseminating pathogens, locally restricted infections did not elicit NK cell IL-10. Thus systemic infections uniquely engage NK cells in an IL-10-mediated immunoregulatory circuit that functions to alleviate inflammation.