Fungal infections in the compromised host--an overview

Potential use of (1,3)-beta-D-glucan as target of diagnosis and treatment of keratomycosis

PURPOSE

Major problems in the management of keratomycosis stem from the difficulty of its diagnosis and limited choice of antifungal agents. In the present paper we propose a new method of detecting (1,3)-beta-D-glucan, one of the major components of fungal cell wall, in tears from an animal model of keratomycosis. In addition, we investigated the efficacy of topical application of micafungin, a new antifungal agent that inhibits the activity of (1,3)-beta-D-glucan synthase in this animal model.

METHOD

Candida albicans (5 x 10(5) organisms) was inoculated into the corneal stroma of 20 New Zealand White rabbits. The animals were randomly assigned to two groups and treated with subconjunctival injection of 0.5 mL of saline or 0.1% micafungin every day for 3 weeks. The clinical course of keratomycosis in both groups was compared. Before and 3 weeks after the injection of saline or micafungin, 5 microL of tears in each eye were collected by capillary tube. The concentration of (1,3)-beta-D-glucan was quantitatively measured by modified Limulus test.

RESULTS

The concentration of (1,3)-beta-D-glucan was significantly higher in keratomycosis model animals than in controls (mean +/- SD, 17.4 +/- 9.4 pg/mL and 2.8 +/- 1.8 pg/mL, respectively) at 21 days after treatment. Subconjunctival injection of micafungin had no significant effect on ocular lesions of keratomycosis until 9 days, after which ocular lesions significantly improved. Subconjunctival application of micafungin decreased the concentration of (1,3)-beta-D-glucan in tears to 4.9 +/- 3.0 pg/mL at 21 days after treatment.

CONCLUSIONS

Increased levels of (1,3)-beta-D-glucan in tears were detected in this model of keratomycosis. Measuring the concentration of (1,3)-beta-D-glucan in tears may be a reliable noninvasive method for the diagnosis of keratomycosis. Topical application of micafungin was effective in the treatment of keratomycosis.

Differential pattern of infection and immune response during experimental oral candidiasis in BALB/c and DBA/2 (H-2d) mice

We used an experimental model of oral candidiasis in the mouse to investigate the impact of the introduction of Candida albicans into a Candida-free system. We report that 2 strains of mice with the same major histocompatibility complex haplotype (H-2d) display different kinetics of primary oral infection after topical application of the same inoculum. The mucosal reactions in both DBA/2 and BALB/c mice involve a similar recruitment of CD4+ and CD8+ T cells and of MAC-1+ cells in mucosal tissue during the infection. A carrier state is maintained following the resolution of the infection in both strains and is associated with the persistence of intraepithelial CD4+ T cells. However, there is a time-specific recruitment of gamma delta T cells that coincides with a dramatic decrease in viable Candida in the mucosal tissue; this occurs on day 3 in BALB/c mice and on day 6 in DBA/2 mice. The denouement of an oral contact with Candida is also different in the 2 mouse strains, cell-mediated immunity being triggered in DBA/2 mice but not in BALB/c mice. The different kinetics of Candida clearance in BALB/c vs DBA/2 mice may therefore signal a differential priming of T cell subsets whose modalities do not appear to be associated with the H-2 complex.

Acquired resistance and persistence of Candida albicans following oral candidiasis in the mouse: a model of the carrier state in humans

In our experimental model of oral candidiasis in the CD1 mouse, the primary infection showed reproducible Candida overgrowth kinetics with a peak level on day 5 of the infection. After day 7, the population stabilized at about 300 colony-forming units per excised mucosal tissue. The primary infection triggered an inflammatory response that resolved in under 8 days. At this point, the histological pattern of the mucosa reached a new equilibrium between recruited and resident mononuclear cells. The primary infection also rapidly stimulated cellular immunity, as measured from day 4 by a delayed-type hypersensitivity footpad reaction. Following a second topical challenge with Candida 30 days after the primary infection, the infection was barely detectable and a typical local delayed-type hypersensitivity reaction occurred between 24-72 h. It is proposed that acquired resistance, in conjunction with low-level persistence of Candida in our model, mimics the carrier state in sensitized humans.

Granulocyte-macrophage colony-stimulating factor augments neutrophil killing of Torulopsis glabrata and stimulates neutrophil respiratory burst and degranulation

The effects of granulocyte-macrophage colony-stimulating factor (GM-CSF) on the interaction between the fungus Torulopsis glabrata and human neutrophils was examined. Pre-incubation of neutrophils with GM-CSF increased the neutrophil fungal killing. The cytokine also increased the oxygen-dependent respiratory burst in response to opsonized fungi, measured by the lucigenin-dependent chemiluminescence assay and superoxide release. Under the same conditions the cytokine augmented release of constituents from both specific and azurophilic granules. Besides these priming effects, GM-CSF was a weak stimulus of the neutrophil respiratory burst and degranulation. The priming and stimulatory effects of GM-CSF were observed at 10-1000 U/ml with an optimal concentration of 100 U/ml.

Evaluation of immunity

Immunodeficiency disease is rapidly increasing in frequency. The AIDS epidemic, the increasing use of transplantation with immunosuppression, the aggressive immunotherapy, the persistent deficiencies after bone marrow transplantation--all contribute to the astronomically increasing numbers of patients with host defense failure. This review has presented my viewpoint as to the approaches which can be utilized by practitioners with varying focal points to provide diagnosis and maximize the potential for a cure today or at least to provide the beginnings of understanding from which will come the cures of tomorrow.