Cryptococcosis. In: Murphy JW, Friedman H, Bendinelli M, editors. Fungal Infections and Immune Responses. Boston: Springer US; 1993. pp. 277-302. [DOI: 10.1007/978-1-4899-2400-1_11]

Contribution of the myeloperoxidase-dependent oxidative system to host defence against Cryptococcus neoformans

The in vivo contribution of reactive oxygen species produced by neutrophils against Cryptococcus infection is not widely recognized. Myeloperoxidase (MPO) is a neutrophil-specific enzyme that catalyses the production of hypohalous acids such as HOCl from H2O2. This study investigated the role of MPO in immunological defence against Cryptococcus neoformans in an MPO-deficient (MPO-/-) mouse model. The survival of MPO-/- mice infected either intranasally or intravenously with C. neoformans was lower than that of identically challenged wild-type mice. The MPO-/- mice that received intranasal injection of C. neoformans had significantly larger lung fungal burdens than wild-type mice. On day 7, MPO-/- mice had a significantly higher lung concentration of interleukin (IL)-4 and lower concentrations of IL-2, IL-12p70 and interferon (IFN)-gamma than wild-type mice, suggesting a weak Th1 response in the MPO-/- mice to C. neoformans. Pathologically, the MPO-/- mice with intranasal infection showed more severe pneumonia than wild-type mice, which was associated with an increase in the levels of IL-1alpha/beta in the lungs. In addition, in MPO-/- mice, the pulmonary infection disseminated to the brain with occasional meningitis. The keratinocyte-derived cytokine (KC) level in the brain of infected MPO-/- mice was higher than that of control mice. Both intranasal and intravenous infections resulted in a higher number of fungi in the spleen of MPO-/- mice compared to wild-type, suggesting decreased resistance to C. neoformans not only in the lungs but also in the spleen in the absence of MPO. Taken together, these data suggest a major role of MPO in the response to cryptococcal infection.

Involvement of CD4+ T cells and macrophages in acquired protection against infection with Sporothrix schenckii in mice

The cell-mediated immune response against infection with Sporothrix schenckii was investigated in vivo and in vitro. Following primary infection, mice were protected against a secondary subcutaneous inoculation with S. schenckii as determined by the local growth of fungi, and subcutaneously immunized mice were able to survive a lethal intravenous infection. Protection could be transferred to naive congenitally athymic nude mice using lymph node cells taken from immune mice. When immune lymph node cells had CD4+ cells depleted by antibody plus complement, the ability to transfer protection was significantly reduced. Treatment of mice with carrageenan, a macrophage blocker, before and after secondary inoculation abolished protection. An in vitro system, using either immune lymph node cells alone or macrophages alone, failed to kill the organism. However, inhibition of fungal growth was observed when both immune lymph node cells and macrophages were combined. Growth inhibition in vitro was reduced after depletion of CD4+ cells but not CD8+ cells. Addition of anti-interferon (IFN)-gamma monoclonal antibodies (MAb) also reduced growth inhibition. By using reverse transcription-polymerase chain reaction (RT-PCR) analysis, it was shown that immune lymph node cells expressed message for IFN-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-10 after stimulation with heat-killed S. schenckii. These results suggest that acquired immunity against S. schenckii is expressed mainly by macrophages activated by CD4+ T cells.

Decreased resistance to primary intravenous Cryptococcus neoformans infection in aged mice despite adequate resistance to intravenous rechallenge

It is often stated that impaired immune functions in the aged underlie their greater susceptibility to infections. Indeed, in many experimental settings, T-cell responses in aged mice have been shown to be deficient compared with those from young adults. Nonetheless, there are very few examples where a greater susceptibility to infection in aged mice has been demonstrated to result from impaired T-cell function. The clinical importance of understanding the basis for increased susceptibility to infection that accompanies advanced age dictates a need for experimental models with which to study the effect that aging has on immunological resistance to infection. This study was undertaken to investigate whether aged mice were less resistant than young adult control mice to infection with the fungus Cryptococcus neoformans. After a primary intravenous challenge with yeast, aged mice died sooner and developed higher organ burdens of yeast than did young adults. Deficient in vitro responses were observed in T cells from aged mice; however, greater susceptibility to intravenous infection appeared not to result from less effective T-cell-dependent resistance in vivo. In fact, T-cell-replete aged mice were more susceptible to intravenous cryptococcal infection than were T-cell-depleted young adults. Furthermore, aged mice were as resistant to primary pulmonary challenge with Cryptococcus as were young adults. Similarly, vaccinated aged mice were as resistant to rechallenge as were young adult counterparts. Therefore, despite demonstrably deficient in vitro responses of T cells from aged mice, their T-cell-dependent resistance to C. neoformans is as effective as that of young adults.

Acquired resistance to Cryptococcus neoformans in adult mice vaccinated as newborns

Although Cryptococcus neoformans causes serious infections in AIDS patients, cryptococcosis in immunologically immature infants, as in immunocompetent adults, is rare. To investigate the resistance of neonates to C. neoformans and to determine whether they could be efficiently vaccinated as neonates against challenge with the yeast as adults, the course of infection was monitored in the lungs of mice infected intranasally with yeast cells. Neonates were less able than adults to reduce yeast burdens less than 24 h postinoculation and less able to control the progressive growth of yeast over several weeks. However, in both neonates and adults, yeasts were substantially eradicated by 6 to 8 weeks after infection. Numbers of all classes of leukocytes recovered from lung lavages of infected neonates and adults were similar. Significant differences appeared only on day 14, when neonates had more neutrophils and adults had significantly more CD4+ CD45RB cells with low fluorescence intensity. When vaccinated neonates were rechallenged after reaching adulthood, they expressed resistance to C. neoformans as effectively as did mice immunized as adults and survived an intravenous challenge that was lethal for unimmunized controls. Thus, exposure of neonatal mice to viable C. neoformans yeast, which persists in the lungs for many weeks, does not result in immunological tolerance to a yeast challenge in adult mice, as predicted by immunological dogma, but instead immunizes them. Therefore, even in immunologically immature individuals, the immune system serves to protect against pathogens rather than simply to distinguish self from nonself.

[Lethal meningeal encephalitis from Cryptococcus neoformans var. neoformans in a girl without serious immunodeficiency]

Case report on a lethal meningo-encephalitis due to Cryptococcus neoformans in a 14-year-old girl without serious immunodeficiency inclusive HIV-infection. The detection of high quantities of cells of Cryptococcus neoformans (about 10,000/ml) and high levels of Cryptococcus antigen (up to 1:2048) in the cerebrospinal fluid are remarkable. The patient was treated with a triple combination of amphotericin B, flucytosine and fluconazole. After 18 days the cerebrospinal fluid was sterile. Nevertheless considerable lesions of the brain arised. The patient died from the Cryptococcus infection on day 74 of the antimycotic therapy. Cryptococcosis should be included into the differential diagnosis of the chronic lymphocytic pleocytosis of the cerebrospinal fluid connected with symptoms of intracranial pressure and ocular symptoms.

Resistance to Cryptococcus neoformans is associated with an inflammatory response to Toxoplasma gondii in the central nervous system of mice

We have studied the resistance of Toxoplasma gondii-infected mice to subsequent infection with Cryptococcus neoformans. Mice infected with the moderately virulent ME49 strain of T. gondii are resistant to proliferation of yeast cells in their brains after intravenous inoculation of the serotype A C. neoformans strain 184. The resistance serves to limit proliferation of yeast cells that colonize the brain. Maximal levels of resistance correlate not with maximal systemic specific anti-Toxoplasma resistance but rather with high levels of inflammatory response, presumably to parasites released from cysts in the brain. Resistance is localized, as mice infected with ME49 show only limited resistance in their lungs after intratracheal instillation of yeast cells, but there is substantial protection against development of cerebral cryptococcosis.