[Show abstract][Hide abstract] ABSTRACT: Rats and mice are considered resistant and susceptible hosts, respectively, for experimental cryptococcosis. For both species, alveolar macrophages (AM) are central components of the host response to pulmonary Cryptococcus neoformans infection. We explored the role of AM in three strains of mice and three strains of rats during cryptococcal infection by comparing the outcome of infection after macrophage depletion using liposomal clodronate. AM depletion was associated with enhancement and amelioration of disease in rats and mice, respectively, as measured by lung fungal burden. The apparent protective role for AM in rats correlated with enhanced anti-cryptococcal activity as measured by phagocytic activity, oxidative burst, lysozyme secretion, and ability to limit intracellular growth of C. neoformans. Furthermore, rat AM were more resistant to lysis in association with intracellular infection. In summary, differences in AM function in rats and mice suggest an explanation for the species differences in susceptibility to C. neoformans based on the inherent efficacy of a central effector cell of the innate immune system.
Full-text · Article · Oct 2005 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: The production of melanin pigments is associated with virulence for many microbes. Melanin is believed to contribute to microbial
virulence by protecting microbial cells from oxidative attack during infection. However, there is also evidence from various
systems that melanins have immunomodulatory properties, which conceivably could contribute to virulence by altering immune
responses. To investigate the effect of melanin on the immune response, we compared the murine pulmonary responses to infection
with melanized and nonmelanized Cryptococcus neoformans cells. Infection with melanized cells resulted in a greater fungal burden during the early stages of infection and was associated
with higher levels of interleukin-4 and MCP-1 and greater numbers of infiltrating leukocytes. Infection with laccase-positive
(melanotic) C. neoformans cells also elicited higher MCP-1 levels and more infiltrating leukocytes than did infection with laccase-negative cells.
Melanization interfered with phagocytosis in vivo for encapsulated C. neoformans but not for nonencapsulated cells. The results provide strong evidence that cryptococcal melanization can influence the immune
response to infection and suggest that immunomodulation is an additional mechanism by which the pigment contributes to virulence.
Preview · Article · May 2005 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: Aspergillus fumigatus causes invasive disease in severely immunocompromised hosts but is readily cleared when host innate defenses are intact. Animal models for evaluation of therapeutic strategies to combat invasive aspergillosis that closely mimic human disease are desirable. We determined optimal dosing regimens for neutrophil depletion and evaluated the course of infection following aerosol infection in mice by determining survival, organ fungal burden, and histopathology in mice in which neutropenia was induced by three methods, administration of granulocyte-depleting monoclonal antibody RB6-8C5 (MAb RB6), administration of cyclophosphamide, and administration of both agents. Administration of either individual agent resulted in a requirement for relatively high conidial inocula to achieve 100% mortality in both BALB/c and C57BL/6 mice, although the infection appeared to be somewhat more lethal in C57BL/6 mice. Death following induction of neutropenia with MAb RB6 occurred when a relatively low fungal burden was present in the lung and may have been related to the inflammatory response associated with neutrophil recovery. In contrast, administration of both agents reduced the lethal inoculum in each mouse strain by approximately 1 log(10), and C57BL/6 mice that received both agents had a higher fungal burden and less inflammation in the lung at the time of death than BALB/c mice or mice of either strain that received MAb RB6 alone. Our data suggest that the relationship among fungal burden, inflammation, and death is complex and can be influenced by the immunosuppression regimen, the mouse strain, and the inoculum.
Full-text · Article · Feb 2005 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: Cryptococcus neoformans is a fungal pathogen that survives in diverse environments. To determine whether cages of mice infected with C. neoformans posed an infection risk to animal caregivers, we investigated whether the fungus could be isolated from the bedding or stool of mice infected by intratracheal (i.t.), intravenous (i.v.), or intraperitoneal (i.p.) routes. The bedding of mice infected i.t. was contaminated with C. neoformans. In contrast, no contamination of bedding with C. neoformans was detected in cages of mice infected i.v. or i.p. C. neoformans was not isolated from murine feces. The C. neoformans strain recovered from bedding material was indistinguishable from the infecting strain by biochemical and molecular techniques. This result suggests that precautions may be warranted when disposing bedding from cages that housed mice with pulmonary C. neoformans infection.
No preview · Article · Aug 2003 · Contemporary topics in laboratory animal science / American Association for Laboratory Animal Science
[Show abstract][Hide abstract] ABSTRACT: Neutrophils are generally considered to contribute to host defense through their potent microbicidal activity. However, there is accumulating evidence that neutrophils also have an important regulatory role in establishing the balance of Th1 and Th2 responses. This study investigated the role of neutrophils in defense against pulmonary Cryptococcus neoformans infection using neutrophil-depleted BALB/c mice generated by administering mAb RB6-8C5. Neutropenic mice with pulmonary infection survived significantly longer than control mice, but there was no difference between groups infected intravenously. On day 1 of infection, neutropenic mice had significantly smaller fungal burdens than control mice. On day 7, neutropenic mice had significantly higher lung concentrations of IL-10, TNF-alpha, IL-4, and IL-12 than control mice, but there was no difference in IFN-gamma and MCP-1 levels. Neutrophils influenced the outcome of cryptococcal infection in mice through mechanisms that did not involve a reduction in early fungal burden. The absence of neutrophils in lung tissue during the initial stages of infection appeared to alter the inflammatory response in a manner that was subsequently beneficial to the host. Higher levels of Th1- and Th2-associated cytokines in neutropenic mice could have simultaneously promoted a strong cellular response while reducing inflammatory damage to the lung. Our results support the emerging concept that neutrophils play an important function in modulating the development of the immune response.
No preview · Article · Jul 2003 · European Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: Cryptococcus neoformans, an encapsulated yeast, is a common cause of life-threatening meningoencephalitis in immunosuppressed patients. We previously observed that administration of a monoclonal antibody (MAb) to the capsular polysaccharide to mice with pulmonary infection prolonged survival and enhanced granulomatous inflammation without reducing lung CFU. To understand the mechanism of MAb action, we studied leukocyte recruitment and cytokine profiles in lungs of A/JCr mice. B lymphocytes were the predominant cell type in lung infiltrates, comprising 15 to 30% of the leukocytes. Despite alterations in histological appearance, fluorescence-activated cell sorter analysis revealed no significant difference in total numbers of lung leukocytes in MAb-treated mice and controls. Differences in the immune response to C. neoformans between MAb-treated mice and controls included (i) an increase in the percentage of granulocytes among lung leukocytes on day 14, (ii) higher macrophage surface expression of CD86 on day 28, (iii) larger amounts of IL-10 in lung homogenates at day 7, (iv) a trend toward smaller amounts of gamma interferon mRNA and protein on day 7, and (v) a smaller increase in the levels of interleukin-4 mRNA and protein on day 7. Hence, the immune responses to C. neoformans infection in the presence and absence of specific antibody were qualitatively similar, and antibody administration was associated with several subtle quantitative differences in immune response parameters that could translate into enhanced survival. MAb may function partly by down-regulating the inflammatory response and reducing host damage. Our findings demonstrate unexpected complexity in the interaction between specific MAb and other components of the host immune response.
Preview · Article · Apr 2002 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: The echinocandin derivative caspofungin (MK-0991, L-743,872)inhibits 1,3-β-D-glucan synthesis and is active against several medically important fungi but is relatively ineffective against Cryptococcus neoformans. To investigate the mechanism of C. neoformans resistance, the prevalence of 1,3- and 1,6-β-D-glucan linkages was determined in cells grown with and without caspofungin, using affinity-purified antisera and gold particle
immunoelectron microscopy. Cryptococcal strains ATCC 24067 (serotype D) and MY2061 (serotype A) were studied. Growth at 4
µg/mL of caspofungin reduced both glucan linkages in both strains. However, growth at 2 µg/mL resulted in reduced 1,6-β-D-glucan linkage only for MY2061. Inhibition of 1,6-β-D-glucan synthesis may be an additional mechanism of action for pneumocandins. The relatively low efficacy of caspofungin against
C. neoformans may result from reduced activity against C. neoformans glucan synthase or from yet undiscovered mechanisms of action operative in other fungal pathogens but not in C. neoformans.
No preview · Article · Jan 2001 · The Journal of Infectious Diseases
[Show abstract][Hide abstract] ABSTRACT: Fungal pathogens are notorious for causing chronic and latent infections, but the mechanism by which they evade the immune
response is poorly understood. A major limitation in the study of chronic fungal infection has been the lack of suitable animal
models where the infection is controlled and yet persists. Pulmonary Cryptococcus neoformans infection in rats results in a diffuse pneumonitis that resolves without dissemination or scarring except for the persistence
of interstitial and subpleural granulomas that harbor viable cryptococci inside macrophages and epithelioid cells. Infected
rats are asymptomatic but remain infected for as long as 18 months after inoculation with C. neoformans. Containment of infection is associated with granuloma formation that can be partially abrogated by glucocorticoid administration.
Using this model, we identified several features associated with persistent infection in the rat lung, including (i) localization
of C. neoformans to discrete, well-organized granulomas; (ii) intracellular persistence ofC. neoformans within macrophages and epithelioid cells; (iii) reduced inducible nitric oxide synthase expression by granulomas harboring
C. neoformans; and (iv) reduced antibody responses to cryptococcal polysaccharide. The results show that maintenance of persistent infection
is associated with downregulation of both cellular and humoral immune responses.
Full-text · Article · Mar 2000 · Infection and Immunity
[Show abstract][Hide abstract] ABSTRACT: Lipoarabinomannan (LAM) is a component of the mycobacterial surface which has been associated with a variety of deleterious effects on immune system function. Despite the importance of LAM to the pathogenesis of mycobacterial infection, there is no information available on its fate in vivo. In this study, we determined the pharmacokinetics and tissue distribution of exogenously administered LAM in mice. For measurements of serum and tissue LAM concentrations, we developed an enzyme-linked immunosorbent assay which used monoclonal antibodies of different isotypes to capture and detect LAM at concentrations of >/=0.4 microg/ml. Intravenous administration of LAM to mice resulted in transient serum levels with organ deposition in the spleen and in the liver. Immunohistochemical studies localized LAM to the spleen marginal zone macrophages and, to a lesser degree, to liver macrophages. When LAM was administered to mice previously given a LAM-binding immunoglobulin M (IgM), LAM was very rapidly cleared from circulation. In those mice, deposition of LAM in the spleen was significantly reduced while LAM deposition in the liver increased. Administration of LAM-binding IgM resulted in significant levels of IgM to LAM in bile consistent with an increased hepatobiliary excretion of LAM in the presence of specific antibody. Bile, liver extracts, and bile salts were found to rapidly inactivate the immunoreactivity of LAM. The results indicate that serum clearance and organ deposition of LAM in mice are affected by the presence of LAM-binding antibody and suggest a mechanism by which antibody could modify the course of mycobacterial infection.
Preview · Article · Jan 2000 · Infection and Immunity