Cytokines in the treatment of fungal infections

Importance of antifungal drug-resistance: clinical significance and need for novel therapy

The incidence of fungal infections has increased dramatically over the past few decades due to the increase in the members of the population susceptible to such infections. This population includes individuals undergoing chemotherapy for cancer, those enduring long-term treatment with antibacterial agents, those receiving immunosuppressive drugs following transplantations, or those immunosuppressed due to diseases, such as AIDS, or malignancies. Newer antifungal agents, namely the triazoles, have aided in both the treatment of fungal infections and in the prevention of disease in susceptible individuals. However, resistance to the azoles, as well as to the polyenes, has resulted in clinical failures. Only a few potential antifungal targets have been exploited to date and there is a critical need for the discovery and development of novel antifungal agents that will result in improved therapy in this ever-expanding patient population. An increased intensity in the study of fungal pathogens at the molecular level holds the key to such advances.

Concanavalin A enhances phagocytosis and killing of Candida albicans by mice peritoneal neutrophils and macrophages

In this study we tested the hypothesis that after administration of a single intraperitoneal dose of concanavalin A (Con-A) to mice, the proportion of neutrophils and macrophages in the peritoneal exudate and their phagocytic and candidacidal activities should change with time. The number of neutrophils in the peritoneal exudate was greatly increased 6 h after administration of Con-A, and those cells were able to kill both intracellular and extracellular yeast and germ tube forms of Candida albicans. Addition of catalase to the culture medium reduced the killing of C. albicans, suggesting that the candidacidal activity depended on the myeloperoxidase system. The survival of mice pretreated with Con-A and submitted to an inoculum of C. albicans 6 h afterwards was twice higher than that of controls, which suggests that neutrophils were able to clear the experimental infection. One day after the treatment, the population of neutrophils in the exudate was about 45%, but after 2 days it was reduced to only 5% and the candidacidal activity was also reduced. After 4 days the exudate contained over 95% of macrophages, the candidacidal activity reached a maximum, and the phagocytosis mediated by both complement receptors and mannose receptors was increased. Uptake of FITC-mannose-BSA by macrophages was maximal on about the 4th day and was inhibited by mannan, suggesting that treatment with Con-A increased the activity of mannose receptors. These results support the hypothesis that activation of cellular immunity by Con-A occurred in two phases, one dominated by neutrophils, and the other by macrophages expressing increased activity of mannose receptors.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

Trends in immunotherapy of fungal infections

Fungal infections are the primary cause of mortality in patients with severely impaired host defense mechanisms, such as neutropenic patients with acute leukemia or those who have undergone bone marrow transplantation. In view of the unacceptably high mortality due to disseminated candidiasis, it is rational to focus on augmentation of host defense mechanisms in addition to conventional antifungal therapy. In vitro, a variety of immunomodulators, including tumor necrosis factor, interferon-g, and the hematopoietic growth factors, enhance the killing of Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans. Various studies have demonstrated beneficial effects of immunomodulatory therapy in animal models of disseminated candidiasis. For further preclinical and clinical studies, recombinant interferon-g, interleukin-1, granulocyte colony-stimulating factor, and the other hematopoietic growth factors are currently the most promising immunomodulators.

Gamma interferon protects endothelial cells from damage by Candida albicans by inhibiting endothelial cell phagocytosis

Once Candida albicans comes in contact with endothelial cells, it induces cellular injury. This endothelial cell injury may be a mechanism by which blood-borne organisms escape from the intravascular compartment and invade the tissue parenchyma during hematogenous infection. We have been investigating the ability of cytokines to modulate endothelial cell injury caused by C. albicans. Previously we reported that pretreatment of endothelial cells with gamma interferon (IFN-gamma) protects these cells from candidal injury in vitro. In the current study, we examined potential mechanisms of the cytoprotective effects of IFN-gamma. Time course experiments demonstrated that maximal reduction in candidal injury of endothelial cells occurred after the endothelial cells had been exposed to IFN-gamma for at least 72 h. In other studies, we determined that IFN-gamma reduced endothelial cell phagocytosis of C. albicans by 41.3% compared with that of untreated endothelial cells (P < 0.01). Since endothelial cell phagocytosis of C. albicans is required for damage to occur, inhibition of phagocytosis is likely a mechanism by which IFN-gamma protects endothelial cells from candidal injury. We also found that the cytoprotective effect of IFN-gamma is not mediated by reducing access of the organisms to intracellular endothelial cell iron or by upregulating the synthesis of reactive oxygen intermediates (which could potentially reduce the ability of C. albicans to injure endothelial cells). Thus, inhibiting endothelial cell phagocytosis of C. albicans may be a mechanism by which IFN-gamma augments the host defense against hematogenously disseminated candidal infections.

Reproductive effects of chronic administration of murine interferon-gamma

Daily subcutaneous doses of 0.02, 0.2, or 2 mg/kg/d of recombinant murine interferon-gamma (rmuIFN-gamma) were given to mice on postnatal days 8 through 60 to determine effects on maturation, behavioral/ functional development, and reproductive capacity. Male mice receiving 2 mg/kg/d rmuIFN-gamma had delayed sexual maturation, reduced epididymal and testes weights, reduced sperm count and concentration, and sperm abnormalities (crimped flagellum). Mating performance and fertility were also reduced in the absence of altered histopathology of the testes. Males given 0.2 and 2 mg/kg/d had swelling and ulcerative dermatitis around the urogenital area, which were observed after sexual contact and attributed to a bacterial infection. Motor activity (time spent in movement) was decreased in all mice receiving 2 mg/kg/d. No microscopic changes observed in any organs were attributed to rmuIFN-gamma administration.

Recent progress and current problems in treatment of invasive fungal infections in neutropenic patients

Invasive fungal infections, including disseminated candidiasis and invasive pulmonary aspergillosis, are important causes of morbidity and mortality in neutropenic patients. The recent development of fluconazole, itraconazole, lipid formulations of amphotericin B, and recombinant cytokines have expanded our therapeutic armamentarium. Clinical trials have elucidated new strategies for utilizing these compounds in the prevention and treatment of opportunistic mycoses. The population of more severely immunocompromised patients, however, continues to expand and the spectrum of drug-resistant fungi, including but not limited to Candida spp, Fusarium spp, Zygomycetes, and dematiaceous moulds, continues to evolve, thus presenting new challenges to recent therapeutic advances. Development of new antifungal chemotherapeutic agents and novel approaches for augmentation of host response will be required to meet these new mycologic challenges.