Intracellular redox-modulated pathways as targets for effective approaches in the treatment of viral infection

Host-directed therapy using drugs that target cellular pathways required for virus lifecycle or its clearance might represent an effective approach for treating infectious diseases. Changes in redox homeostasis, including intracellular glutathione (GSH) depletion, are one of the key events that favor virus replication and contribute to the pathogenesis of virus-induced disease. Redox homeostasis has an important role in maintaining an appropriate Th1/Th2 balance, which is necessary to mount an effective immune response against viral infection and to avoid excessive inflammatory responses. It is known that excessive production of reactive oxygen species (ROS) induced by viral infection activates nuclear factor (NF)-kB, which orchestrates the expression of viral and host genes involved in the viral replication and inflammatory response. Moreover, redox-regulated protein disulfide isomerase (PDI) chaperones have an essential role in catalyzing formation of disulfide bonds in viral proteins. This review aims at describing the role of GSH in modulating redox sensitive pathways, in particular that mediated by NF-kB, and PDI activity. The second part of the review discusses the effectiveness of GSH-boosting molecules as broad-spectrum antivirals acting in a multifaceted way that includes the modulation of immune and inflammatory responses

Cryptococcus neoformans Capsular Enlargement and Cellular Gigantism during Galleria mellonella Infection

We have studied infection of Cryptococcus neoformans in the non-vertebrate host Galleria mellonella with particular interest in the morphological response of the yeast. Inoculation of C. neoformans in caterpillars induced a capsule-independent increase in haemocyte density 2 h after infection. C. neoformans manifested a significant increase in capsule size after inoculation into the caterpillar. The magnitude of capsule increase depended on the temperature, being more pronounced at 37°C than at 30°C, which correlated with an increased virulence of the fungus and reduced phagocytosis at 37°C. Capsule enlargement impaired phagocytosis by haemocytes. Incubation of the yeast in G. mellonella extracts also resulted in capsule enlargement, with the polar lipidic fraction having a prominent role in this effect. During infection, the capsule decreased in permeability. A low proportion of the cells (<5%) recovered from caterpillars measured more than 30 µm and were considered giant cells. Giant cells recovered from mice were able to kill the caterpillars in a manner similar to regular cells obtained from in vivo or grown in vitro, establishing their capacity to cause disease. Our results indicate that the morphological transitions exhibited by C. neoformans in mammals also occur in a non-vertebrate host system. The similarities in morphological transitions observed in different animal hosts and in their triggers are consistent with the hypothesis that the cell body and capsular responses represent an adaptation of environmental survival strategies to pathogenesis

Purified capsular polysaccharide of Cryptococcus neoformans induces interleukin-10 secretion by human monocytes.

In this study, we demonstrated that purified capsular polysaccharide of Cryptococcus neoformans is a potent inducer of interleukin-10 (IL-10) secretion by human monocytes. Endogenous IL-10 was involved in regulating tumor necrosis factor alpha and IL-1beta secretion by human monocytes in response to encapsulated C. neoformans strains. Our results suggest a new immunosuppressive effect exerted by glucuronoxylomannan through the induction of IL-10, a potent downregulator of proinflammatory cytokines

Regulatory role of exogenous IL-10 in the development of immune response versus Cryptococcus neoformans

The most important event involved in host defence against Cryptococcus neoformans is the development of an adequate cell-mediated immune response. IL-10, abundantly produced during AIDS progression, could be a negative factor that affects the T cell response through its own immunosuppressive action on antigen-presenting cells. To determine whether this cytokine affects the course of immune response against C. neoformans, we added exogenous IL-10 to cultured Cryptococcus-laden monocytes plus T lymphocytes. The data from this study confirmed the down-regulatory effect of exogenous IL-10 on monocytes and expanded the known inhibitory role to include an increase of the deleterious effect due to capsular material of C. neoformans on (i) lymphoproliferation, (ii) down-regulation of MHC class II molecules, (iii) inhibition of IL-2 mRNA expression and protein secretion by T lymphocytes. These results indicate that the presence of IL-10 in AIDS patients, due to the progression of disease, could represent a pivotal problem contributing to augment the pathogenic effect of C. neoformans

Capsular polysaccharide of Cryptococcus neoformans induces proinflammatory cytokine release by human neutrophils.

Human polymorphonuclear leukocytes from normal subjects produced proinflammatory cytokines in response to stimulation with Cryptococcus neoformans yeast cells. The cytokines released after stimulation of neutrophils included interleukin-1beta (IL-1beta), IL-6, IL-8 and tumor necrosis factor alpha. The magnitude of the cytokine response was related to the yeast capsule size. Cells of a large-capsule isolate stimulated release of greater amounts of cytokine than did a thinly encapsulated isolate, which, in turn, stimulated release of greater amounts of cytokine than an acapsular isolate. Cytokine release was also stimulated by supernatant fluids from cryptococcal cells that were preincubated with 10% human serum, suggesting the generation of a soluble mediator. The major capsular polysaccharide, glucuronoxylomannan, stimulated release of tumor necrosis factor alpha, IL-1beta, and IL-8 in a dose-dependent fashion. These results differ from previous studies of cytokine secretion by human monocytes in several important respects, including the importance of encapsulation in stimulation of cytokine secretion and the ability of purified glucuronoxylomannan to induce cytokine secretion

Inhibition of fungicidal activity of polymorphonuclear leukocytes from HIV-infected patients by interleukin (IL)-4 and IL-10

Objective: To investigate the effect of human recombinant interleukin (hrIL)-4 or hrIL-10 on the functional status of polymorphonuclear leukocytes (PMNL) from normal subjects and HIV-infected patients. Design: In an in vitro system we studied the effect of hrIL-4 and hrIL-10 on phagocytosis, fungicidal activity and superoxide anion production by PMNL. Methods: PMNL were treated in vitro with hrIL-4 or hrIL-10 or their combination for 6 h and then candidacidal activity was evaluated in a colony-forming unit inhibition assay. Superoxide anion generation by PMNL was measured in the presence or absence of preopsonized zymosan or Candida albicans. Results: Treatment in vitro with hrIL-4 or hrIL-10 of PMNL for 6 h was able to impair candidacidal activity of neutrophils in both normal or HIV-infected patients. The inhibitory effect was time- and dose-dependent and was more evident in PMNL from HIV-infected subjects, and reflected in these latter cells a decrease of superoxide anion generation. The impairment of candidacidal activity in PMNL from HIV-infected patients was accompanied by survival of the yeasts shown by budding formation into phagosomic organelles of cytokine-treated PMNL. Conclusions: Our data highlight new biological effects of IL-4 and IL-10 evidenced by suppressed effector function of neutrophils; this phenomenon is emphasized in HIV-infected patients suggesting a role for these cytokines in mediating increased susceptibility to microbial infection during AIDS progression

BENEFICIAL EFFECT OF RECOMBINANT HUMAN GRANULOCYTE-COLONY-STIMULATING FACTOR ON FUNGICIDAL ACTIVITY OF POLYMORPHONUCLEAR LEUKOCYTES FROM PATIENTS WITH AIDS

The effect of recombinant human granulocyte colony-stimulating factor (rhG-CSF) administration on the functional status of polymorphonuclear leukocytes (PMNL) in neutropenic AIDS patients was investigated. PMNL destructive activity against Candida albicans or encapsulated or acapsular Cryptococcus neoformans was significantly impaired with respect to control subjects before rhG-CSF treatment. After subcutaneous administration of rhG-CSF (5 mu g/kg), neutrophil counts increased 3- to 11-fold in 24 h and returned to baseline within 96 h. PMNL fungicidal activity showed significant enhancement 48-72 h after rhG-CSF administration that decreased to baseline within 96 h. Enhanced rhG-CSF-mediated destructive activity strictly correlated with augmented superoxide anion production by PMNL. These findings suggest that therapeutic use of rhG-CSF at appropriate schedules in neutropenic AIDS patients could decrease the risk of infection or, in association with antibiotic therapy, more rapidly resolve the occurring infections