Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Interleukin-10 and the interleukin-10 receptor.

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that expand during cancer, inflammation and infection, and that have a remarkable ability to suppress T-cell responses. These cells constitute a unique component of the immune system that regulates immune responses in healthy individuals and in the context of various diseases. In this Review, we discuss the origin, mechanisms of expansion and suppressive functions of MDSCs, as well as the potential to target these cells for therapeutic benefit.

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Myeloid-derived suppressor cells as regulators of the immune system.

The expanding universe of T-cell subsets: Th1, Th2 and more

Infectious Diseases Society of America.

Eukaryotic cells can initiate several distinct programmes of self-destruction, and the nature of the cell death process (non-inflammatory or proinflammatory) instructs responses of neighbouring cells, which in turn dictates important systemic physiological outcomes Pyroptosis, or caspase 1-dependent cell death, is inherently inflammatory, is triggered by various pathological stimuli, such as stroke, heart attack or cancer, and is crucial for controlling microbial infections Pathogens have evolved mechanisms to inhibit pyroptosis, enhancing their ability to persist and cause disease Ultimately, there is a competition between host and pathogen to regulate pyroptosis, and the outcome dictates life or death of the host

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Pyroptosis: host cell death and inflammation

To define the role of interleukin (IL)6 in Candida albicans infection, IL-6 deficient mice were assessed for susceptibility to systemic or gastrointestinal infection, as well as for parameters of elicited T helper cell (Th) immunity. IL-6-deficient mice were more susceptible than wild-type mice to either type of infection caused by virulent C. albicans. In response to systemic challenge with a live vaccine strain of yeast, IL-6-deficient mice failed to mount Th1-associated protective immunity, but the resulting Th2-biased response could be redirected to the Th1 phenotype by IL-10 neutralization. Severe impairment of the macrophage and neutrophil response to infection was observed in IL-6-deficient mice, but administration of IL-6 would increase both neutrophil response and resistance to infection. IL-6 seems to oppose the Th2-promoting role of IL-10 in candidiasis, its early regulatory activity involving effects on neutrophil function.

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Impaired neutrophil response and CD4+ T helper cell 1 development in interleukin 6-deficient mice infected with Candida albicans.

Mouse peritoneal and splenic macrophages treated with interferon-gamma (IFN-gamma) and infected with the yeast Candida albicans expressed high fungicidal activity in vitro that correlated with increased nitrite concentrations in culture supernatants. Both effects were reduced by an inhibitor of nitric oxide (NO) synthesis which, in vivo, impaired the animals' ability to mount a footpad reaction and clear the fungus from infected organs. Because T helper type-2 (Th2) cytokines in candidiasis are known to limit the expression of protective Th1 functions, we tested the effect of interleukin (IL)-4 and IL-10 on candidacidal activity and NO production of IFN-gamma-activated macrophages. Fungal killing and NO secretion were inhibited, in a dose-dependent manner, by the two cytokines either separately or in combination. Impaired candidacidal activity was also demonstrable in the presence of monoiodoacetic acid, an inhibitor of phagocytosis. These data demonstrate that NO is involved in macrophage killing of C. albicans and support the notion that regulation of Th1 effector function by IL-4 and IL-10 might involve modulation of NO synthesis.

Interleukin-4 and interleukin-10 inhibit nitric oxide-dependent macrophage killing of Candida albicans.

Systemic infection of mice with a Candida albicans strain (PCA-2) incapable of yeast-mycelial conversion conferred protection against a subsequent intravenous challenge with the pathogenic strain of the parent organism, strain CA-6. Protection was nonspecific since it was also detected upon challenge of mice with Staphylococcus aureus. Moreover, the PCA-2 organisms had to be viable, their effects being most evident when they were given intravenously at a dose of 10(6) cells 7 to 14 days prior to microbial challenge. Thus, all mice pretreated with PCA-2 and challenged 14 days later with viable CA-6 cells lived through a 60-day observation period, whereas all control mice not treated with PCA-2 died within 3 days. In an attempt to correlate the immunostimulatory effects observed in vivo with possible modifications in in vitro functions, it was found that administration of PCA-2 was accompanied by an increase in the number of peripheral blood polymorphonuclear cells and by the activation in the spleen of cells with highly candidacidal activity in vitro. Moreover, the adoptive transfer of plastic-adherent cells from PCA-2-infected mice into histocompatible recipients conferred considerable protection against subsequent CA-6 challenge.

https://iai.asm.org/content/iai/51/2/668.full.pdf

Evidence for macrophage-mediated protection against lethal Candida albicans infection.

The role of cytokine- and T helper (Th)-dependent lung mucosal antifungal immunity in murine invasive pulmonary aspergillosis (IPA) was investigated. Intact or leukopenic DBA/2 mice were resistant or highly susceptible, respectively, to infection caused by multiple intranasal injections of viable Aspergillus fumigatus conidia. Resistance was associated with unimpaired innate antifungal activity of pulmonary phagocytic cells, concomitant with high-level production of tumor necrosis factor (TNF)-alpha and interleukin (IL)-12 and the presence of interstitial lymphocytes producing interferon-gamma and IL-2. Conversely, production of TNF-alpha and IL-12 was down-regulated in highly susceptible mice, which also had defective innate antifungal immunity and high-level production of IL-4 and IL-10 by lung lymphocytes. Resistance was increased in susceptible mice upon local IL-4 or IL-10 neutralization or IL-12 administration. These results indicate that, similar to observations in mice with disseminated aspergillosis, innate and Th1-dependent immunity play an essential role in host defense against IPA.

Cytokine- and T Helper-Dependent Lung Mucosal Immunity in Mice with Invasive Pulmonary Aspergillosis

With a murine model of invasive aspergillosis we investigated cytokine production by CD4+ T helper cells and the effects of cytokine administration or neutralization on the course and outcome of infection. Patterns of susceptibility and resistance to infection were obtained with different strains of mice injected with different inocula of Aspergillus fumigatus conidia. Mice surviving the primary infection also resisted a subsequent lethal infection that was associated with production of gamma interferon by CD4+ T splenocytes. Impaired neutrophil antifungal activity, observed in susceptible mice, was concomitant with a predominant production of interleukin-4 (IL-4) by CD4+ splenocytes. In these mice, exogenous administration of IL-12 failed to induce resistance to infection; in contrast, treatment with soluble IL-4 receptor cured more than 70% of the mice from primary infection and resulted in the onset of acquired resistance to a subsequent lethal infection. These findings indicate that in murine invasive aspergillosis, production of IL-4 by CD4+ T cells may be one major factor discriminating susceptibility and resistance to infection.

https://iai.asm.org/content/iai/65/2/564.full.pdf

Elio Cenci

Papers

Impaired neutrophil response and CD4+ T helper cell 1 development in interleukin 6-deficient mice infected with Candida albicans.

Interleukin-4 and interleukin-10 inhibit nitric oxide-dependent macrophage killing of Candida albicans.

Evidence for macrophage-mediated protection against lethal Candida albicans infection.

Cytokine- and T Helper-Dependent Lung Mucosal Immunity in Mice with Invasive Pulmonary Aspergillosis

Th1 and Th2 cytokines in mice with invasive aspergillosis.