Similar to hematopoietic stem cells, memory lymphocytes self-renew, while their clonally expanded effector progeny differentiate to fight infection and tumors. Recently, Muranski et al.(2011) report in Immunity that a subset of Th17 effector cells function as memory cells and retain stem cell properties.

Regulatory B cells that are functionally defined by their capacity to express IL-10 (B10 cells) downregulate inflammation and autoimmunity. In studies using well-defined IL-10 reporter mice, this rare B10 cell subset was also found to maintain a capacity for plasma cell differentiation. During a transient period of il10 transcription, the blimp1 and irf4 transcription factors were induced in B10 cells, whereas pax5 and bcl6 were downregulated as a significant fraction of B10 cells completed the genetic and phenotypic program leading to Ab-secreting cell differentiation in vitro and in vivo. B10 cell-derived IgM reacted with both self- and foreign Ags, whereas B10 cells generated Ag-specific IgG in response to immunizations. Moreover, B10 cells represented a significant source of serum IgM and IgG during adoptive-transfer experiments and produced Ag-specific, polyreactive and autoreactive Ab specificities that were consistent with their expression of a diverse AgR repertoire. Thereby, B10 cells limit inflammation and immune responses by the transient production of IL-10, and may facilitate clearance of their eliciting Ags through an inherent capacity to quickly generate polyreactive and/or Ag-specific Abs during humoral immune responses.

The interleukin-17 (IL-17) family of cytokines phylogenetically predates the evolution of T cells in jawed vertebrates, suggesting that the ontogeny of the Th17 cell lineage must have arisen to confer an evolutionary advantage to the host over innate sources of IL-17. Utilizing a model of mucosal immunization with the encapsulated bacteria Klebsiella pneumoniae, we found that B cells, which largely recognized polysaccharide capsular antigens, afforded protection to only the vaccine strain. In contrast, memory Th17 cells proliferated in response to conserved outer membrane proteins and conferred protection against several serotypes of K. pneumoniae, including the recently described multidrug resistant New Dehli metallolactamase strain. Notably, this heterologous, clade-specific protection was antibody independent, demonstrating the Th17 cell lineage confers a host advantage by providing heterologous mucosal immunity independent of serotype-specific antibody.

Infections with HIV, hepatitis B virus, and hepatitis C virus can turn into chronic infections, which currently affect more than 500 million patients worldwide. It is generally thought that virus-mediated T-cell exhaustion limits T-cell function, thus promoting chronic disease. Here we demonstrate that natural killer (NK) cells have a negative impact on the development of T-cell immunity by using the murine lymphocytic choriomeningitis virus. NK cell-deficient (Nfil3(-/-), E4BP4(-/-)) mice exhibited a higher virus-specific T-cell response. In addition, NK cell depletion caused enhanced T-cell immunity in WT mice, which led to rapid virus control and prevented chronic infection in lymphocytic choriomeningitis virus clone 13- and reduced viral load in DOCILE-infected animals. Further experiments showed that NKG2D triggered regulatory NK cell functions, which were mediated by perforin, and limited T-cell responses. Therefore, we identified an important role of regulatory NK cells in limiting T-cell immunity during virus infection.

B cells contribute to the pathogenesis of chronic autoimmune disorders, like systemic lupus erythematosus (SLE), via multiple effector functions. However, B cells are also implicated in regulating SLE and other autoimmune syndromes via release of IL-10. B cells secreting IL-10 were termed "Bregs" and were proposed as a separate subset of cells, a concept that remains controversial. The balance between pro- and anti-inflammatory effects could determine the success of B cell-targeted therapies for autoimmune disorders; therefore, it is pivotal to understand the significance of B cell-secreted IL-10 in spontaneous autoimmunity. By lineage-specific deletion of Il10 from B cells, we demonstrated that B cell-derived IL-10 is ineffective in suppressing the spontaneous activation of self-reactive B and T cells during lupus. Correspondingly, severity of organ disease and survival rates in mice harboring Il10-deficient B cells are unaltered. Genetic marking of cells that transcribe Il10 illustrated that the pool of IL-10-competent cells is dominated by CD4 T cells and macrophages. IL-10-competent cells of the B lineage are rare in vivo and, among them, short-lived plasmablasts have the highest frequency, suggesting an activation-driven, rather than lineage-driven, phenotype. Putative Breg phenotypic subsets, such as CD1d(hi)CD5(+) and CD21(hi)CD23(hi) B cells, are not enriched in Il10 transcription. These genetic studies demonstrated that, in a spontaneous model of murine lupus, IL-10-dependent B cell regulation does not restrain disease and, thus, the pathogenic effects of B cells are not detectably counterbalanced by their IL-10-dependent regulatory functions.

Human neonates are at significantly greater risk of serious infection than immunocompetent adults. In particular, very low birth weight infants in the neonatal intensive care nursery are at high risk of developing life-threatening bacterial and fungal infections. Recent studies have identified Th17 cells as critical mediators of immunity to bacterial and fungal infections at epithelial barriers. Little is known, however, about the ontogeny of Th17-cell responses in humans. The frequency of serious bacterial infections in preterm infants and the importance of Th17 cells in providing protection against such infections in animal studies prompted us to study Th17-cell development in human neonates. Naïve CD4(+) T cells from extremely preterm infants, term infants, and adults were assayed for their capacity to develop into Th17 effector cells. Surprisingly, Th17-cell capacity was inversely related to developmental age. Neonates expressed higher levels of IL-23R, RORγt, and STAT3 prior to activation and showed a significant Th17-cell bias after activation. In contrast, adult cells expressed more TBX21 with a corresponding Th1-cell bias. CD161 expression on Th17-cell precursors was also developmentally regulated. Our results suggest there is significant developmental regulation of CD4(+) effector lineages with a strong bias toward Th17-cell development early in life.

We have previously reported that mice deficient in the beta-glucan receptor Dectin-1 displayed increased susceptibility to Aspergillus fumigatus lung infection in the presence of lower interleukin 23 (IL-23) and IL-17A production in the lungs and have reported a role for IL-17A in lung defense. As IL-23 is also thought to control the production of IL-22, we examined the role of Dectin-1 in IL-22 production, as well as the role of IL-22 in innate host defense against A. fumigatus. Here, we show that Dectin-1-deficient mice demonstrated significantly reduced levels of IL-22 in the lungs early after A. fumigatus challenge. Culturing cells from enzymatic lung digests ex vivo further demonstrated Dectin-1-dependent IL-22 production. IL-22 production was additionally found to be independent of IL-1β, IL-6, or IL-18 but required IL-23. The addition of recombinant IL-23 augmented IL-22 production in wild-type (WT) lung cells and rescued IL-22 production by lung cells from Dectin-1-deficient mice. In vivo neutralization of IL-22 in the lungs of WT mice resulted in impaired A. fumigatus lung clearance. Moreover, mice deficient in IL-22 also demonstrated a higher lung fungal burden after A. fumigatus challenge in the presence of impaired IL-1α, tumor necrosis factor alpha (TNF-α), CCL3/MIP-1α, and CCL4/MIP-1β production and lower neutrophil recruitment, yet intact IL-17A production. We further show that lung lavage fluid collected from both A. fumigatus-challenged Dectin-1-deficient and IL-22-deficient mice had compromised anti-fungal activity against A. fumigatus in vitro. Although lipocalin 2 production was observed to be Dectin-1 and IL-22 dependent, lipocalin 2-deficient mice did not demonstrate impaired A. fumigatus clearance. Moreover, lung S100a8, S100a9, and Reg3g mRNA expression was not lower in either Dectin-1-deficient or IL-22-deficient mice. Collectively, our results indicate that early innate lung defense against A. fumigatus is mediated by Dectin-1-dependent IL-22 production.

We have previously reported that compromised interleukin 17A (IL-17A) production in the lungs increased susceptibility to infection with the invasive fungal pathogen Aspergillus fumigatus. Here we have shown that culturing lung cells from A. fumigatus-challenged mice ex vivo demonstrated Dectin-1-dependent IL-17A production. In this system, neutralization of IL-23 but not IL-6, IL-1β, or IL-18 resulted in attenuated IL-17A production. Il23 mRNA expression was found to be lower in lung cells from A. fumigatus-challenged Dectin-1-deficient mice, whereas bone marrow-derived dendritic cells from Dectin-1-deficient mice failed to produce IL-23 in response to A. fumigatus in vitro. Addition of recombinant IL-23 augmented IL-17A production by wild-type (WT) and Dectin-1-deficient lung cells, although the addition of IL-6 or IL-1β did not augment the effect of IL-23. Intracellular cytokine staining of lung cells revealed lower levels of CD11b(+) IL-17A(+) and Ly-6G(+) IL-17A(+) cells in A. fumigatus-challenged Dectin-1-deficient mice. Ly-6G(+) neutrophils purified from the lungs of A. fumigatus-challenged Dectin-1-deficient mice displayed lower Il17a mRNA expression but surprisingly had intact Rorc and Rora mRNA expression. We further demonstrated that Ly-6G(+) neutrophils required the presence of myeloid cells for IL-17A production. Finally, upon in vitro stimulation with A. fumigatus, thioglycolate-elicited peritoneal neutrophils were positive for intracellular IL-17A expression and produced IL-17A in a Dectin-1- and IL-23-dependent manner. In summary, Dectin-1-dependent IL-17A production in the lungs during invasive fungal infection is mediated in part by CD11b(+) Ly-6G(+) neutrophils in an IL-23-dependent manner.

Levels of reactive free radicals are elevated in the airway during asthmatic exacerbations, but their roles in the pathophysiology of asthma remain unclear. We have identified subsets of myeloid-derived suppressor-like cells as key sources of nitric oxide and superoxide in the lungs of mice with evolving experimental allergic airway inflammation and established these cells as master regulators of the airway inflammatory response. The profiles of free radicals they produced depended on expression of inducible nitric oxide synthase (iNOS), arginase, and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. These radicals controlled the pro- and anti-inflammatory potential of these cells, and also regulated the reciprocal pattern of their infiltration into the lung. The nitric oxide-producing cells were Ly-6C(+)Ly-6G(-) and they downmodulated T-cell activation, recruited T(reg) cells, and dramatically downregulated antigen-induced airway hyperresponsiveness. The superoxide-producing cells were Ly-6C(-)Ly-6G(+) and they expressed proinflammatory activities, exacerbating airway hyperresponsiveness in a superoxide-dependent fashion. A smaller population of Ly-6C(+)Ly-6G(+) cells also suppressed T-cell responses, but in an iNOS- and arginase-independent fashion. These regulatory myeloid cells represent important targets for asthma therapy.Mucosal Immunology advance online publication 6 April 2011, doi:10.1038/mi.2011.16.

BACKGROUND & AIMS Regulatory T (Treg) cells are plastic, but the in vivo mechanisms by which they are converted into foxhead box p3 (Foxp3+) interferon (IFN)-γ+ T cells and whether these converted cells retain the ability to inhibit colitis are not clear. METHODS Foxp3+ Treg cells were generated by culture of naïve CD4+ T cells from Foxp3GFP CBir1 T-cell receptor (TCR) transgenic (Tg)(CBir1-Tg) mice, which are specific for CBir1 flagellin (an immunodominant microbiota antigen), with transforming growth factor-β. Foxp3GFP+ CBir1-Tg Treg cells were isolated by fluorescence-activated cell sorting and transferred into TCRβxδ-/- mice. Colitis was induced by transfer of naïve CBir1-Tg CD4+ T cells into immunodeficient mice. RESULTS Microbiota antigen-specific Foxp3+ Treg cells were converted, in the intestine, to IFN-γ+ T-helper (Th)1 cells, interleukin (IL)-17+ Th17 cells, and Foxp3+ T cells that coexpress IFN-γ and/or IL-17. Conversion of Treg cells into IFN-γ-producing Th1 cells and Foxp3+IFN-γ+ T cells required innate cell production of IL-12 in the intestine; blocking IL-12 with an antibody inhibited their conversion to Th1 and Foxp3+IFN-γ+ T cells in the intestines of mice that were recipients of Treg cells. Addition of IL-12, but not IL-23, promoted conversion of Treg cells into Th1 and Foxp3+IFN-γ+ T cells, in vitro. Foxp3+IFN-γ+ T cells had regulatory activity because they suppressed proliferation of naïve T cells, in vitro, and inhibited induction of colitis by microbiota antigen-specific T cells. IFN-γ+ Th1 cells were not converted into Treg cells; Foxp3+IFN-γ+ T cells differentiated into IFN-γ+ but not Foxp3+ T cells. CONCLUSIONS IL-12 promotes conversion of Treg cells into IFN-γ-expressing cells; Foxp3+IFN-γ+ T cells retain their regulatory functions and develop during the transition of Foxp3+ Treg cells into IFN-γ+ Th1 cells.