Zinc Induces Dendritic Cell Tolerogenic Phenotype and Skews Regulatory T Cell-Th17 Balance.

Zinc (Zn) is an essential metal for development and maintenance of both the innate and adaptive compartments of the immune system. Zn homeostasis impacts maturation of dendritic cells (DCs) that are important in shaping T cell responses. The mechanisms by which Zn regulates the tolerogenic phenotype of DCs remain largely unknown. In this study, we investigated the effect of Zn on DC phenotype and the generation of Foxp3(+) regulatory T cells (Tregs) using a model of Histoplasma capsulatum fungal infection. Exposure of bone marrow-derived DCs to Zn in vitro induced a tolerogenic phenotype by diminishing surface MHC class II (MHCII) and promoting the tolerogenic markers, programmed death-ligand (PD-L)1, PD-L2, and the tryptophan degrading enzyme, IDO. Zn triggered tryptophan degradation by IDO and kynurenine production by DCs and strongly suppressed the proinflammatory response to stimulation by TLR ligands. In vivo, Zn supplementation and subsequent H. capsulatum infection supressed MHCII on DCs, enhanced PD-L1 and PD-L2 expression on MHCII(lo) DCs, and skewed the Treg-Th17 balance in favor of Foxp3(+) Tregs while decreasing Th17 cells. Thus, Zn shapes the tolerogenic potential of DCs in vitro and in vivo and promotes Tregs during fungal infection.

Comparison of a new triazole antifungal agent, Schering 56592, with itraconazole and amphotericin B for treatment of histoplasmosis in immunocompetent mice.

A murine model of intratracheally induced histoplasmosis was used to evaluate a new triazole antifungal agent, Schering (SCH) 56592, for treatment of histoplasmosis. MICs were determined for SCH 56592, amphotericin B, and itraconazole by testing yeast-phase isolates from 20 patients by a macrobroth dilution method. The MICs at which 90% of the isolates are inhibited were for 0.019 microgram/ml for SCH 56592, 0.5 microgram/ml for amphotericin B, and < or = 0.019 microgram/ml for itraconazole. Survival studies were done on groups of 10 B6C3F1 mice with a lethal inoculum of 10(5). All mice receiving 5, 1, or 0.25 mg of SCH 56592 per kg of body weight per day, 2.5 mg of amphotericin B per kg every other day (qod), or 75 mg of itraconazole per kg per day survived to day 29. Only 44% of mice receiving 5 mg of itraconazole/kg/day survived to day 29. Fungal burden studies done in similar groups of mice with a sublethal inoculum of 10(4) showed a reduction in CFUs and Histoplasma antigen levels in lung and spleen tissue in animals treated with 2 mg of amphotericin B/kg qod, 1 mg of SCH 56592/kg/day, and 75 mg of itraconazole/kg/day, but not in those treated with lower doses of the study drugs (0.2 mg of amphotericin B/kg qod, 0.1 mg of SCH 56592/kg/day, or 10 mg of itraconazole/kg/day). Serum drug concentrations were measured 3 and 24 h after the last dose in mice (groups of five to seven mice), each treated for 7 days with SCH 56592 (10 and 1 mg/kg/day) and itraconazole (75 and 10 mg/kg/day). Mean levels measured by bioassay were as follows: SCH 56592, 10 mg/kg/day (2.15 micrograms/ml at 3 h and 0.35 microgram/ml at 24 h); SCH 56592, 1 mg/kg/day (0.54 microgram/ml at 3 h and none detected at 24 h); itraconazole, 75 mg/kg/day (22.53 micrograms/ml at 3 h and none detected at 24 h); itraconazole, 10 mg/kg/day (1.33 micrograms/ml at 3 h and none detected at 24 h). Confirmatory results were obtained by high-pressure liquid chromatography assay. These studies show SCH 56592 to be a promising candidate for studies of treatment of histoplasmosis in humans.

Clearance of Histoplasma capsulatum variety capsulatum antigen is useful for monitoring treatment of experimental histoplasmosis.

We sought to determine whether measurement of Histoplasma capsulatum var. capsulatum antigen concentration in tissues and blood provided a marker for antifungal effect of itraconazole in a nonlethal murine model of histoplasmosis. Treatment with itraconazole (Sporanox), in cyclodextrin, was evaluated in a pulmonary model of histoplasmosis. Mice infected with 4.0 x 10(7) yeast-phase organisms by endotracheal inoculation were treated with itraconazole, 1.5 mg twice daily by gavage, for 10 consecutive days, beginning on day 4 of infection. All mice were sacrificed on day 15 of infection. Blood, spleen, and lung tissues were removed for culture and quantification of antigen. Numbers of organisms were significantly lower in spleens from the treated group: 20.8 +/- 41.8 vs. 65.8 +/- 39.1 in the control group, P = 0.017. Numbers of organisms in lung were 9.6 +/- 27.3 colony forming units in treated versus 24.2 +/- 36.3 in control animals, P = 0.267. Antigen concentrations in spleen tissue and serum were lower in treated versus control mice: spleen, 1.8 +/- .6 units in treated versus 11.0 +/- 2.3 in controls, P < 0.001; serum, 0.8 +/- 0.2 units in treated versus 2.2 +/- 1.0 units in controls, P < 0.001. Lung antigen concentrations were similar in the two groups, 19.2 +/- 1.4 units in treated compared to 17.9 +/- 3.0 units in control mice, P = 0.142. The cyclodextrin formulation of itraconazole (Sporanox) demonstrated antifungal activity in experimental histoplasmosis. Antigen detection was a useful marker for antifungal effect.

Protective effect of poly-2-vinylpyridine-N-oxide on susceptibility of silica-treated mice to experimental histoplasmosis.

We have studied the ability of poly-2-vinylpyridine-N-oxide (PVNO), a lysosomal stabilizing agent, to abrogate the cytotoxic effects of silica on macrophages. Male C3H/HeN mice were pretreated with PVNO and inoculated intravenously with silica particles. At 24 h after silica injection, silica-treated and -untreated mice were challenged intravenously with varying doses of live yeast cells of Histoplasma capsulatum. All mice receiving silica died when challenged with 5 X 10(5) yeast cells of Histoplasma sp. compared with no deaths in PVNO-pretreated animals and 10% mortality in controls not receiving PVNO or silica. When animals were given 2.5 X 10(5) yeast cells (a sublethal dose), the protective effect of PVNO was seen by a reduction in splenomegaly and viable Histoplasma sp. present in the spleen. Furthermore, PVNO alone showed a significant protective effect (P less than 0.05) against a lethal challenge with Histoplasma sp. Prior treatment with PVNO also protected mouse peritoneal macrophages from the cytotoxic effects of silica particles in vitro. These results indicate that PVNO abrogates the cytotoxicity of silica particles on macrophages and also increases the resistance of mice to histoplasmosis.