transforming-growth-factor-beta and Cryptococcosis

The effects of capsular polysaccharides, galactoxylomannan (GalXM) and glucuronoxylomannan (GXM), from acapsular (GXM negative) and encapsulate strains of Cryptococcus neoformans were investigated in RAW 264.7 and peritoneal macrophages. Here, we demonstrate that GalXM and GXM induced different cytokines profiles in RAW 264.7 macrophages. GalXM induced production of TNF-alpha, NO and iNOS expression, while GXM predominantly induced TGF-beta secretion. Both GalXM and GXM induced early morphological changes identified as autophagy and late macrophages apoptosis mediated by Fas/FasL interaction, a previously unidentified mechanism of virulence. GalXM was more potent than GXM at induction of Fas/FasL expression and apoptosis on macrophages in vitro and in vivo. These findings uncover a mechanism by which capsular polysaccharides from C. neoformans might compromise host immune responses.

Topics: Animals; Apoptosis; Bacterial Capsules; Cells, Cultured; Cryptococcosis; Cryptococcus neoformans; Fas Ligand Protein; Macrophages; Mice; Mice, Inbred BALB C; Nitric Oxide; Nitric Oxide Synthase Type II; Polysaccharides; Polysaccharides, Bacterial; Transforming Growth Factor beta; Tumor Necrosis Factor-alpha

Respiratory infections are the third leading cause of death worldwide. Complications arise directly as a consequence of pathogen replication or indirectly due to aberrant or excessive immune responses. In the following report, we evaluate the efficacy, in a murine model, of nasally delivered DNA encoding TGF-beta1 to suppress immunopathology in response to a variety of infectious agents. A single nasal administration suppressed lymphocyte responses to Cryptococcus neoformans, influenza virus and respiratory syncytial virus. The suppression did not depend on the phenotype of the responding T cell, since both Th1 and Th2 responses were affected. During Th2-inducing infection, pulmonary eosinophilic responses were significantly suppressed. In all cases, however, suppressed immunity correlated with increased susceptibility to infection. We conclude that nasal TGF-beta treatment could be used to prevent pulmonary, pathogen-driven eosinophilic disease, although anti-pathogen strategies will need to be administered concordantly.

Topics: Animals; Cryptococcosis; Female; Gene Expression; Inflammation; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Orthomyxoviridae Infections; Plasmids; Pulmonary Eosinophilia; Respiratory Syncytial Virus Infections; T-Lymphocytes, Helper-Inducer; Transforming Growth Factor beta

TGF-beta1 (TGF) has been implicated in the pathogenesis of several chronic infections and is thought to promote microbial persistence by interfering with macrophage function. In rats with experimental pulmonary cryptococcosis, increased lung levels of TGF were present at 12 mo of infection. Within the lung, expression of TGF localized to epithelioid cells and foamy macrophages in areas of inflammation. Increased TGF expression was also observed in the lungs of experimentally infected mice and a patient with pulmonary cryptococcosis. TGF reduced Ab and serum-mediated phagocytosis of Cryptococcus neoformans by rat alveolar macrophages (AM) and peripheral blood monocytes, and this was associated with decreased chemokine production and oxidative burst. Interestingly, TGF-treated rat AM limited both intracellular and extracellular growth of C. neoformans. Control of C. neoformans growth by TGF-treated rat AM was due to increased secretion of lysozyme, a protein with potent antifungal activity. The effects of TGF on the course of infection were dependent on the timing of TGF administration relative to the time of infection. TGF treatment of chronically infected rats resulted in reduced lung fungal burden, while treatment early in the course of infection resulted in increased fungal burden. In summary, our studies suggest a dual role for TGF in persistent fungal pneumonia whereby it contributes to the local control of infection by enhancing macrophage antifungal efficacy through increased lysozyme secretion, while limiting inflammation by inhibiting macrophage/monocyte phagocytosis and reducing associated chemokine production and oxidative burst.

Topics: Animals; Cell Line; Chemokines; Child; Cryptococcosis; Cryptococcus neoformans; Female; Humans; Immunohistochemistry; Lung Diseases, Fungal; Macrophages, Alveolar; Male; Mice; Mice, Inbred C57BL; Muramidase; Phagocytosis; Rats; Rats, Inbred F344; Recombinant Proteins; Respiratory Burst; Transforming Growth Factor beta; Transforming Growth Factor beta1

Rats, like humans, have extremely effective immune mechanisms for controlling pulmonary Cryptococcus neoformans infection. The mechanism(s) responsible for efficient immunity in rat experimental infection is unknown. Recently, induction of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) have been implicated as an important microbicidal mechanism by which activated macrophages effect cytotoxicity against microbes. In this report, we investigated the expression of iNOS in rat pulmonary cryptococcosis. Localization and regulation of NO production was studied by immunohistochemistry for iNOS in conjunction with immunohistochemistry for cell markers, cytokines, and cryptococcal capsular polysaccharide. iNOS immunoreactivity was detected in macrophages, neutrophils, vascular endothelium, and respiratory epithelium. Double-immunolabeling studies revealed that the most prominent iNOS immunoreactivity was localized to epithelioid macrophages (CD11b/c+) within granulomas; CD4+ and CD8+ T cells were numerous around granulomas but did not express iNOS. iNOS immunoreactivity was detected in a selective population of epithelioid macrophages within some granulomas but not others. iNOS- granulomas were identical to iNOS+ granulomas with respect to morphology and immunohistochemical profiles. Macrophage iNOS immunoreactivity was detected 1 week after infection in one out of four rats and was strongly expressed in all rats at 2 weeks (in up to 50 percent of the granulomas) but declined considerably by 25 days. iNOS expression coincided with granuloma formation and preceded a decrease in lung fungal burden, suggesting an anticryptococcal role for NO. By double labeling, cytokines that have been shown to promote (interferon-gamma, granulocyte/macrophage colony-stimulating factor) and inhibit (transforming growth factor-beta) macrophage iNOS expression were detected around iNOS+ granuloma. iNOS immunoreactivity was expressed in selected neutrophils (1 and 2 weeks) and endothelial cells (1 and 2 weeks and 25 days) in the inflamed lung. Airway iNOS immunoreactivity was limited to the luminal border of rare bronchiolar epithelial cells. iNOS immunoreactivity was not detected in uninfected rats. The present study provides the first evidence for association of iNOS expression with protective cellular responses to cryptococcal infection in vivo.

Topics: Animals; Cryptococcosis; Epithelium; Granulocyte-Macrophage Colony-Stimulating Factor; Granuloma; Interferon-gamma; Lung Diseases, Fungal; Macrophages; Male; Neutrophils; Nitric Oxide Synthase; Rats; Rats, Inbred F344; Transforming Growth Factor beta