Control, immunoregulation, and expression of innate pulmonary host defenses against Aspergillus fumigatus.

The innate host defense system (IHDS) against Aspergillus fumigatus includes dedicated phagocytic cells (peripheral blood monocytes, monocyte derived macrophages, pulmonary alveolar macrophages, neutrophils, myeloid dendritic cells and natural killer cells), cytokines, chemokines, toll-like receptors, and antimicrobial peptides. During the past decade, the advances in the field of the IHDS have been enormous, allowing a better understanding of the immunopharmacological control, immunoregulation, and expression of innate host defense molecules against Aspergillus fumigatus.

Pharmacokinetic and pharmacodynamic modeling of anidulafungin (LY303366): reappraisal of its efficacy in neutropenic animal models of opportunistic mycoses using optimal plasma sampling.

The compartmental pharmacokinetics of anidulafungin (VER-002; formerly LY303366) in plasma were characterized with normal rabbits, and the relationships between drug concentrations and antifungal efficacy were assessed in clinically applicable infection models in persistently neutropenic animals. At intravenous dosages ranging from 0.1 to 20 mg/kg of body weight, anidulafungin demonstrated linear plasma pharmacokinetics that fitted best to a three-compartment open pharmacokinetic model. Following administration over 7 days, the mean (+/- standard error of the mean) peak plasma concentration (C(max)) increased from 0.46 +/- 0.02 microg/ml at 0.1 mg/kg to 63.02 +/- 2.93 microg/ml at 20 mg/kg, and the mean area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)) rose from 0.71 +/- 0.04 to 208.80 +/- 24.21 microg. h/ml. The mean apparent volume of distribution at steady state (V(ss)) ranged from 0.953 +/- 0.05 to 1.636 +/- 0.22 liter/kg (nonsignificant [NS]), and clearance ranged from 0.107 +/- 0.01 to 0.149 +/- 0.00 liter/kg/h (NS). Except for a significant prolongation of the terminal half-life and a trend toward an increased V(ss) at the higher end of the dosage range after multiple doses, no significant differences in pharmacokinetic parameters were noted in comparison to single-dose administration. Concentrations in tissue at trough after multiple dosing (0.1 to 10 mg/kg/day) were highest in lung and liver (0.85 +/- 0.16 to 32.64 +/- 2.03 and 0.32 +/- 0.05 to 43.76 +/- 1.62 microg/g, respectively), followed by spleen and kidney (0.24 +/- 0.65 to 21.74 +/- 1.86 and <0.20 to 16.92 +/- 0.56, respectively). Measurable concentrations in brain tissue were found at dosages of > or =0.5 mg/kg (0.24 +/- 0.02 to 3.90 +/- 0.25). Implementation of optimal plasma sampling in persistently neutropenic rabbit infection models of disseminated candidiasis and pulmonary aspergillosis based on the Bayesian approach and model parameters from normal animals as priors revealed a significantly slower clearance (P < 0.05 for all dosage groups) with a trend toward higher AUC(0-24) values, higher plasma concentrations at the end of the dosing interval, and a smaller volume of distribution (P < 0.05 to 0.193 for the various comparisons among dosage groups). Pharmacodynamic modeling using the residual fungal tissue burden in the main target sites as the primary endpoint and C(max), AUC(0-24), time during the dosing interval of 24 h with plasma drug concentration equaling or exceeding the MIC or the minimum fungicidal concentration for the isolate, and tissue concentrations as pharmacodynamic parameters showed predictable pharmacokinetic-pharmacodynamic relationships in experimental disseminated candidiasis that fitted well with an inhibitory sigmoid maximum effect pharmacodynamic model (r(2), 0.492 to 0.819). However, no concentration-effect relationships were observed in experimental pulmonary aspergillosis using the residual fungal burden in lung tissue and survival as parameters of antifungal efficacy. Implementation of optimal plasma sampling in discriminative animal models of invasive fungal infections and pharmacodynamic modeling is a novel approach that holds promise of improving and accelerating our understanding of the action of antifungal compounds in vivo.

Recombinant human macrophage colony-stimulating factor augments pulmonary host defences against Aspergillus fumigatus.

The in vivo and ex vivo effects of macrophage colony-stimulating factor (M-CSF) were studied in a profoundly neutropenic rabbit model in order to determine its potential to augment pulmonary host defence against Aspergillus. M-CSF (100-600 microg/kg/d) was administered prophylactically to neutropenic rabbits with pulmonary aspergillosis starting three days pre-inoculation and then throughout neutropenia. Rabbits receiving M-CSF had significantly increased survival (P=0.01) and decreased pulmonary injury, as measured by decreased pulmonary infarction (P=0.004), when compared with untreated controls. Microscopic studies demonstrated greater numbers of activated pulmonary alveolar macrophages (PAMs) in lung tissue of rabbits receiving M-CSF, in comparison to controls (P<0.001). PAMs harvested from rabbits treated with M-CSF had a significantly greater percent phagocytosis of Aspergillus fumigatus conidia than did PAMs from controls (P=0.04). These data indicate that prophylactic administration of M-CSF augments pulmonary host defence against A. fumigatus and suggest a potential role for this cytokine as adjunctive therapy in the treatment of pulmonary aspergillosis in the setting of profound neutropenia.

Dosage-dependent antifungal efficacy of V-echinocandin (LY303366) against experimental fluconazole-resistant oropharyngeal and esophageal candidiasis.

V-echinocandin (VER-002; LY303366) is a semisynthetic derivative of echinocandin B and a potent inhibitor of fungal (1, 3)-beta-D-glucan synthase. We studied the antifungal efficacy, the concentrations in saliva and tissue, and the safety of VER-002 at escalating dosages against experimental oropharyngeal and esophageal candidiasis caused by fluconazole-resistant Candida albicans in immunocompromised rabbits. Study groups consisted of untreated controls, animals treated with VER-002 at 1, 2.5, and 5 mg/kg of body weight/day intravenously (i.v.), animals treated with fluconazole at 2 mg/kg/day i.v., or animals treated with amphotericin B at 0.3 mg/kg/day. VER-002-treated animals showed a significant dosage-dependent clearance of C. albicans from the tongue, oropharynx, esophagus, stomach, and duodenum in comparison to that for untreated controls. VER-002 also was superior to amphotericin B and fluconazole in clearing the organism from all sites studied. These in vivo findings are consistent with the results of in vitro time-kill assays, which demonstrated that VER-002 has concentration-dependent fungicidal activity. Esophageal tissue VER-002 concentrations were dosage proportional and exceeded the MIC at all dosages. Echinocandin concentrations in saliva were greater than or equal to the MICs at all dosages. There was no elevation of serum hepatic transaminase, alkaline phosphatase, bilirubin, potassium, or creatinine levels in VER-002-treated rabbits. In summary, the echinocandin VER-002 was well tolerated, penetrated the esophagus and salivary glands, and demonstrated dosage-dependent antifungal activity against fluconazole-resistant esophageal candidiasis in immunocompromised rabbits.

Correlation between in vitro and in vivo antifungal activities in experimental fluconazole-resistant oropharyngeal and esophageal candidiasis.

Oropharyngeal and esophageal candidiasis (OPEC) is a frequent opportunistic mycosis in immunocompromised patients. Azole-resistant OPEC is a refractory form of this infection occurring particularly in human immunodeficiency virus (HIV)-infected patients. The procedures developed by the Antifungal Subcommittee of the National Committee for Clinical Laboratory Standards (NCCLS) are an important advance in standardization of in vitro antifungal susceptibility methodology. In order to further understand the relationship between NCCLS methodology and antifungal therapeutic response, we studied the potential correlation between in vitro susceptibility to fluconazole and in vivo response in a rabbit model of fluconazole-resistant OPEC. MICs of fluconazole were determined by NCCLS methods. Three fluconazole-susceptible (FS) (MIC, /=64 microgram/ml) isolates of Candida albicans from prospectively monitored HIV-infected children with OPEC were studied. FR isolates were recovered from children with severe OPEC refractory to fluconazole, and FS isolates were recovered from those with mucosal candidiasis responsive to fluconazole. Fluconazole at 2 mg/kg of body weight/day was administered to infected animals for 7 days. The concentrations of fluconazole in plasma were maintained above the MICs for FS isolates throughout the dosing interval. Fluconazole concentrations in the esophagus were greater than or equal to those in plasma. Rabbits infected with FS isolates and treated with fluconazole had significant reductions in oral mucosal quantitative cultures (P < 0.001) and tissue burden of C. albicans in tongue, soft palate, and esophagus (P < 0.001). In comparison, rabbits infected with FR isolates were unresponsive to fluconazole and had no reduction in oral mucosal quantitative cultures or tissue burden of C. albicans versus untreated controls. We conclude that there is a strong correlation between in vitro fluconazole susceptibility by NCCLS methods and in vivo response to fluconazole therapy of OPEC due to C. albicans.

Antifungal activity of splenic, liver and pulmonary macrophages against Candida albicans and effects of macrophage colony-stimulating factor.

Disseminated infections due to Candida albicans are frequently encountered in immunocompromised patients. We compared the antifungal activities of macrophages residing in spleen, liver and lungs of rabbits against blastoconidia and pseudohyphae of C. albicans. Splenic adherent cells (SAC), Kupffer cells (KC) and pulmonary alveolar macrophages (PAM) all ingested blastoconidia efficiently. SAC caused significantly more damage to unopsonized pseudohyphae compared with KC (P < 0.01) or PAM (P < 0.001). Incubation of SAC with 15 ng ml(-1) of recombinant human macrophage colony-stimulating factor (M-CSF) at 37 degrees C for 2 days significantly enhanced phagocytosis (P = 0.02) and killing (P = 0.05) of blastoconidia. In contrast, M-CSF had no effect on phagocytic activities of KC or PAM against blastoconidia or on damage caused by any of the macrophages to pseudohyphae of C. albicans. Thus, although all three resident macrophage types ingest blastoconidia efficiently, they differ in their capacity to cause damage to pseudohyphae and in their responsiveness to M-CSF for antifungal activation. M-CSF augments the capacity of SAC to ingest and kill blastoconidia and may therefore have a role in the treatment and prevention of hematogenously disseminated candidiasis.

Antifungal activity of LY303366, a novel echinocandin B, in experimental disseminated candidiasis in rabbits.

The safety and antifungal activity of LY303366 (LY), a new broad-spectrum semisynthetic echinocandin, were studied against disseminated candidiasis in persistently neutropenic rabbits. In vitro time-kill assays demonstrated that LY has concentration-dependent fungicidal activity. The pharmacokinetics of LY in the plasma of nonneutropenic rabbits suggested a linear relationship between dose and area under the curve (AUC). The times spent above the MIC during the experimental dosing interval of 24 h were 4 h for LY at 0.1 mg/kg of body weight/day (LY0.1), 8 h for LY at 0.25 mg/kg/day (LY0.25), 12 h for LY at 0.5 mg/kg/day (LY0.5), and 20 h for LY at 1 mg/kg/day (LY1). Antifungal therapy was administered to infected rabbits for 10 days starting 24 h after the intravenous (i.v.) inoculation of 10(3) Candida albicans blastoconidia. Study groups consisted of untreated controls (UCs) and animals treated with amphotericin B (AmB; 1 mg/kg/day i.v.), fluconazole (FLU; 10 mg/kg/day i.v.), and LY0.1, LY0.25, LY0.5, or LY1 i.v. Rabbits treated with LY0.5, LY1, AmB, and FLU had similarly significant clearance of C. albicans from the liver, spleen, kidney, lung, vena cava, and brain in comparison to that for UCs. There was a dose-dependent clearance of C. albicans from tissues in response to LY. Among rabbits treated with LY0.1 there was a significant reduction of C. albicans only in the spleen. In animals treated with LY0.25 there was a significant reduction in all tissues but the brain. By comparison, LY0.5 and LY1 cleared all tissues, including the brain, of C. albicans. These in vivo findings were consistent with the results of in vitro time-kill assays. A dose-dependent effect of altered cell wall morphology was observed among UCs and animals treated with LY0.1, and LY0.25, with a progressive transition from hyphal structure to disrupted yeast forms. Serum creatinine levels were higher and serum potassium levels were lower in AmB-treated rabbits than in UCs and LY- and FLU-treated rabbits. LY0.5 and LY1 were well tolerated, displayed predictable pharmacokinetics in plasma, and had activities comparable to those of AmB and FLU in the treatment of disseminated candidiasis in persistently neutropenic rabbits.

Effects of the hematoregulatory peptide SK&F 107647 alone and in combination with amphotericin B against disseminated candidiasis in persistently neutropenic rabbits.

The effects of the hematoregulatory peptide SK&F 107647 were examined in a persistently and profoundly neutropenic rabbit model of disseminated candidiasis in order to determine its potential to enhance resistance against infection and its role as an adjunct to conventional antifungal chemotherapy. In healthy animals, SK&F 107647 elicited a time-dependent increase in CD11b-positive monocytes and neutrophils. When administered to neutropenic rabbits infected with Candida albicans, no significant differences in the number of CFU per gram in any of the tissues tested compared with the number in untreated control rabbits were detected. However, when SK&F 107647 was administered in combination with low doses of amphotericin B, there was a significant reduction in organism burden in the lungs, liver, spleen, and kidneys compared with the burdens in the organs of untreated control animals and in the lungs and kidneys compared with the burdens in the lungs and kidneys of animals treated with amphotericin B alone. These data suggest a potential role for this peptide as adjunctive therapy in combination with conventional antifungal agents in the treatment of disseminated candidiasis in the setting of profound and persistent neutropenia.

Adherence of Candida albicans to bladder mucosa: development and application of a tissue explant assay.

In order to study the interactions between Candida species and uroepithelial tissue, a tissue explant assay was developed using bladder mucosa harvested from New Zealand white rabbits. Blastoconidia of Candida albicans, Candida tropicalis and Candida glabrata attached to the uroepithelial tissue in similar quantities. However, there was significantly more adherence to the uroepithelium by pre-germinated C. albicans compared with C. albicans blastoconidia. Furthermore, the amount of uroepithelial tissue injury was directly related to the length of exposure of the tissue to Candida. Thus, this tissue explant assay may provide a useful method for investigating properties related to fungal adherence to transitional uroepithelium and organism-mediated tissue injury.

Increased adherence of fluconazole-resistant isolates of Candida species to explanted esophageal mucosa.

The adherence of fluconazole-resistant and fluconazole-susceptible isolates of Candida albicans to explanted rabbit esophageal mucosa was examined in vivo. Among six Candida albicans isolates collected from HIV-infected patients, three fluconazole-resistant (MIC > 64 microg/ml) isolates attached more avidly than three fluconazole-susceptible strains (MIC < or = 0.5 microg/ml) to esophageal mucosa (P < or = 0.05). When three strains each of six different Candida spp. were compared, the more inherently fluconazole-resistant isolates adhered more avidly in the following order: Candida glabrata>Candida krusei>Candida albicans fluconazole-sensitive>Candida tropicalis>Candida parapsilosis. Nonetheless, fluconazole-resistant Candida albicans demonstrated the greatest degree of adherence in comparison to all fluconazole-susceptible Candida albicans (P<0.001) and to all Candida spp. tested (P<0.001). Thus, the refractoriness of esophageal candidiasis in patients infected with fluconazole-resistant isolates may be related to both in vitro drug resistance and increased mucosal adherence.

Antimicrobial peptides as potential new antifungals.

Ribosomally synthesized natural antimicrobial peptides (AP) and their synthetic derivatives are small, cationic, amphipathic molecules of 12-50 amino acids with unusually broad activity spectra. These peptides kill microorganisms by a common mechanism, which involves binding to the lipid bilayer of biological membranes, forming pores, and ultimately followed by cell lysis. Several AP from mammals, amphibians, insects, plants and their synthetic derivatives demonstrate promising in vitro activity against various pathogenic fungi including azole-resistant Candida albicans strains. In addition to their antimicrobial activity, some AP such as lactoferrin, interact with a variety of host cells and can increase the activity of natural killer and lymphokine activated killer cells. Pretreatment of polymorphonuclear neutrophil leukocytes (PMN) or monocytes with these AP also may upregulate superoxide release. AP as potential new antifungal agents offer some advantages, such as rapid killing of pathogenic fungi and the difficulty to raise mutants resistant to these peptides. AP are limited by their nonselective toxicity, stability, immunogenicity and their costs of production. Potential clinical applications of AP in the future have to be further explored in preclinical and clinical studies to assess their impact as a new class of antifungals.

Antimicrobial peptides as potential new antifungals.

Ribosomally synthesized natural antimicrobial peptides (AP) and their synthetic derivatives are small, cationic, amphipathic molecules of 12-50 amino acids with unusually broad activity spectra. These peptides kill microorganisms by a common mechanism, which involves binding to the lipid bilayer of biological membranes, forming pores, and ultimately followed by cell lysis. Several AP from mammals, amphibians, insects, plants and their synthetic derivatives demonstrate promising in vitro activity against various pathogenic fungi including azole-resistant Candida albicans strains. In addition to their antimicrobial activity, some AP such as lactoferrin, interact with a variety of host cells and can increase the activity of natural killer and lymphokine activated killer cells. Pretreatment of polymorphonuclear neutrophil leukocytes (PMN) or monocytes with these AP also may upregulate superoxide release. AP as potential new antifungal agents offer some advantages, such as rapid killing of pathogenic fungi and the difficulty to raise mutants resistant to these peptides. AP are limited by their nonselective toxicity, stability, immunogenicity and their costs of production. Potential clinical applications of AP in the future have to be further explored in preclinical and clinical studies to assess their impact as a new class of antifungals.

Interleukin-15 augments superoxide production and microbicidal activity of human monocytes against Candida albicans.

Interleukin-15 (IL-15) is a newly described cytokine that shares biological activities with IL-2. We report here results demonstrating the ability of IL-15 to enhance superoxide production and antifungal activity of human monocytes. After 18 and 48 h of treatment with IL-15, human elutriated monocytes manifested enhanced superoxide production in response to either phorbol myristate acetate or opsonized Candida albicans blastoconidia. Similar results were obtained when monocytes were treated with IL-2, but to a lesser extent. Combination studies with IL-15 and IL-2 showed no additive or synergistic effects. Following incubation of monocytes with IL-15 for 18 h, there was no significant increase in mRNA transcripts for components of the NADPH oxidase complex, p40-phox, p47-phox, and gp91-phox, suggesting a posttranscriptional modulation of enhanced superoxide production. Antibodies against the gamma chain of the IL-2 receptor and, to a lesser extent, against the beta chain partially abrogated the IL-15-mediated enhanced superoxide production. Additionally, human monocytes showed enhanced killing activity against C. albicans after 18 h of incubation with IL-15 or IL-2, but this treatment did not enhance the ability of these cells to phagocytose the organism. In addition, the enhanced fungicidal activity seen after 18 h of treatment was no longer detectable after 48 h of cytokine treatment. Culture supernatants from the IL-15-treated monocytes were assayed for the presence of other proinflammatory cytokines. IL-15 treatment did not induce the release of detectable levels of tumor necrosis factor alpha, IL-1beta, or IL-12. Our results indicate that IL-15 upregulates the microbicidal activity of human monocytes against C. albicans.

Specific induction of fibronectin binding activity by hemoglobin in Candida albicans grown in defined media.

Fibronectin (FN) is a major component of host extracellular matrix that may play an important role in the initiation and dissemination of Candida albicans infections. Expression of FN binding requires growth of C albicans blastoconidia in complex medium, and the regulation of FN receptor expression is poorly understood. We now demonstrate that hemoglobin is a potent and specific inducer of FN receptor expression and describe a defined medium supplemented with hemoglobin that greatly and stably enhances the binding activity of C. albicans for soluble FN. Enhancement of FN binding by hemoglobin in strain 44807 was concentration dependent and was maximal at 0.1% hemoglobin with 20- to 80-fold enhancement. The hemoglobin-induced FN binding to C. albicans was saturable, with a Kd of 2.7 X 10(-8) M. Enhancement required growth of C. albicans in hemoglobin-containing medium, since simply exposing blastoconidia to hemoglobin in a nongrowing status did not enhance binding. Induction was reversible following removal of hemoglobin from the growth medium and not associated with germination. Inorganic or protein-bound iron was not sufficient for the induction, since other iron-containing proteins or inorganic iron salts were inactive. Growth in the simple medium yeast nitrogen base supplemented with hemoglobin increased cell adhesion to immobilized FN and to cultured monolayers of bovine corneal endothelial cells. These data suggest that hemoglobin may be an important regulator of FN binding activity in C. albicans and thus may play a role in its pathogenesis.

Ex vivo effects of macrophage colony-stimulating factor on human monocyte activity against fungal and bacterial pathogens.

The ex vivo effects of macrophage colony-stimulating factor (M-CSF) on antifungal and antibacterial activities of human elutriated monocytes were studied. Cells were isolated prior to the initiation of therapy, on day 3 and at week 7, in six patients with an advanced malignancy receiving M-CSF in a phase I study. Superoxide anion production by monocytes in response to N-formyl methionyl leucyl phenylalanine was enhanced at day 3 of therapy (P = 0.011). In addition, at day 3, fungicidal activity against blastoconidia of Candida albicans was enhanced by M-CSF treatment (P = 0.026), whereas antifungal activity against hyphae of Aspergillus fumigatus was not significantly changed. Bactericidal activity against Staphylococcus aureus was increased at day 3 (P = 0.004). By Northern blot analysis, M-CSF does not upregulate the expression of components of the NADPH-oxidase, the multicomponent enzyme system responsible for generation of superoxide radicals by monocytes. Instead, the predominant effect of M-CSF on circulating monocytes is probably a post-transcriptional effect. In conclusion, these findings suggest that administration of M-CSF to patients may enhance microbicidal activities and thus may provide a useful adjunct to conventional antimicrobial therapy.

Detection and quantitation of the glucuronoxylomannan-like polysaccharide antigen from clinical and nonclinical isolates of Trichosporon beigelii and implications for pathogenicity.

Sera from patients with systemic infections caused by the opportunistic fungus Trichosporon beigelii have been shown to cross-react with anticryptococcal antibodies. We quantitatively compared the amounts of antigen produced and examined the expression of O-acetyl epitopes from 35 strains of T. beigelii isolated from deep and superficial infections. By counterimmunoelectrophoresis, 10 of 10 isolates from deep infections were positive for polysaccharide, compared with 7 of 13 isolates from superficial infections (P = 0.02). All 23 strains tested were positive for polysaccharide when screened by immunodot. By enzyme immunoassay, the cross-reactive antigen produced by deep isolates (n = 9) had a mean titer of 1:5,500. In contrast, superficial isolates (n = 22) produced significantly less antigen than the deep isolates (P < 0.001), with a mean titer of 1:700. Isolates from environmental sources (n = 3) were similar to the superficial isolates, with a mean titer of 1:600. The mean concentrations +/- standard errors of cross-reactive polysaccharide released by deep isolates and superficial isolates were 3.09 +/- 0.44 and 1.74 +/- 0.30 micrograms/ml, respectively, when measured by rocket immunoelectrophoresis (P = 0.02). O-Acetyl epitopes were detected on polysaccharide from 8 of 9 strains of T. beigelii isolated from deep sources, while only 2 of 12 superficial isolates expressed detectable O-acetyl epitopes (P = 0.01). Thus, while all isolates of T. beigelii tested were capable of producing glucuronoxylomannan-like cross-reactive antigen, pathogenic isolates produced significantly more antigen than superficial or environmental isolates. Furthermore, significantly more pathogenic isolates than superficial or environmental isolates expressed antigen that was O acetylated.

Response of human polymorphonuclear leukocytes and monocytes to Trichosporon beigelii: host defense against an emerging opportunistic pathogen.

To further understand human host defenses against Trichosporon beigelii, functional responses were investigated of polymorphonuclear leukocytes (PMNL) and elutriated human monocytes (EHM) to this opportunistic fungal pathogen. There was significantly less PMNL phagocytosis (P < .001) and killing (P < .001) of T. beigelii isolates than of Candida albicans. However, levels of superoxide anions generated by PMNL in response to T. beigelii and C. albicans were comparable. Pretreatment of PMNL with granulocyte colony-stimulating factor or interferon-gamma (IFN-gamma) did not significantly enhance fungicidal activity. Killing of T. beigelii by EHM also was significantly impaired compared with killing of C. albicans (P < .001). However, pretreatment of EHM with macrophage colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, or IFN-gamma all resulted in enhanced fungicidal activity. Thus, phagocytosis and killing of T. beigelii by PMNL and EHM are significantly less efficient than that of C. albicans. However, monocytes may be more important in the control of Trichosporon species than previously shown.

Phagocytosis of medically important yeasts by polymorphonuclear leukocytes.

Phagocytosis is a critical function of polymorphonuclear leukocytes in the control of mycotic infections. By using a modified fluorescence quenching assay to distinguish between attached and ingested organisms, we determined the percent phagocytosis of several medically important yeasts. The percentages of phagocytosis of serum-opsonized Candida albicans, Candida tropicalis, Candida parapsilosis, and Torulopsis glabrata were all comparable at 37 degrees C. By comparison, there was significantly less phagocytosis of Cryptococcus neoformans and Trichosporon beigelii isolates (P < 0.001). Thus, phagocytosis of C. albicans by polymorphonuclear leukocytes is comparable to that of species other than C. albicans but is significantly greater than that of the basidiomycetous yeasts T. beigelii and C. neoformans.