A rapid [3H]glucose incorporation assay for determination of lymphoid cell-mediated inhibition of Candida albicans growth

Effects of reproductive hormones on experimental vaginal candidiasis

Vulvovaginal candidiasis (VVC) is an opportunistic mucosal infection caused by Candida albicans that affects large numbers of otherwise healthy women of childbearing age. Acute episodes of VVC often occur during pregnancy and during the luteal phase of the menstrual cycle, when levels of progesterone and estrogen are elevated. Although estrogen-dependent experimental rodent models of C. albicans vaginal infection are used for many applications, the role of reproductive hormones and/or their limits in the acquisition of vaginal candidiasis remain unclear. This study examined the effects of estrogen and progesterone on several aspects of an experimental infection together with relative cell-mediated immune responses. Results showed that while decreasing estrogen concentrations eventually influenced infection-induced vaginal titers of C. albicans and rates of infection in inoculated animals, the experimental infection could not be achieved in mice treated with various concentrations of progesterone alone. Furthermore, progesterone had no effect on (i) the induction and persistence of the infection in the presence of estrogen, (ii) delayed-type hypersensitivity in primary-infected mice, or (iii) the partial protection from a secondary vaginal infection under pseudoestrus conditions. Other results with estrogen showed that a persistent infection could be established with a wide range of C. albicans inocula under supraphysiologic and near-physiologic (at estrus) concentrations of estrogen and that vaginal fungus titers or rates of infection were similar if pseudoestrus was initiated several days before or after inoculation. However, the pseudoestrus state had to be maintained for the infection to persist. Finally, estrogen was found to reduce the ability of vaginal epithelial cells to inhibit the growth of C. albicans. These results suggest that estrogen, but not progesterone, is an important factor in hormone-associated susceptibility to C. albicans vaginitis.

Therapeutic efficacy of human macrophage colony-stimulating factor, used alone and in combination with antifungal agents, in mice with systemic Candida albicans infection

We examined the in vivo activity of human macrophage colony-stimulating factor (hM-CSF) against lethal Candida albicans infection in mice. In C. albicans-infected mice which had been immunosuppressed with cyclophosphamide, treatment with hM-CSF at a daily dose of 8 x 10(5) units/kg of body weight or greater slightly but significantly prolonged survival. Furthermore, the therapeutic efficacy of amphotericin B (AMPH-B) in infected mice was enhanced by its combined use with hM-CSF, while that of fluconazole (FLCZ) was not. The activities of peritoneal macrophages and neutrophils from mice administered hM-CSF plus AMPH-B in combination for inhibition of hyphal growth of C. albicans cells and intracellular phagocytosis and killing of the cells were greater than those of comparable phagocytic cells from control mice to which hM-CSF plus AMPH-B was not administered. These results suggest that intravenous administration of hM-CSF augments the efficacy of AMPH-B by enhancing the antifungal activities of macrophages and neutrophils. Therefore, it is expected that therapy with the combination AMPH-B and hM-CSF could improve the efficacy of AMPH-B and reduce the therapeutic dose of the antifungal drug that is required.

Effects of macrophage inhibitory factor-A3 (MIF-A3) on cytokine secretion and phagolysosome fusion in murine macrophages

Macrophage inhibitory factor-A3 (MIF-A3) is a fraction derived from Mycobacterium avium serovar 2 (Mav2) that consists of a small amine containing compound (peptide), trehalose and two or three short chain fatty acids. MIF-A3 has been shown to inhibit candidacidal activity of murine thioglycolate-elicited peritoneal-derived macrophages and bovine peripheral blood monocytes, and scavenge reactive oxygen intermediates. In this study, MIF-A3 was evaluated for its effect on secretion of IL-1beta, IL-6, IL-10, TNFalpha and GM-CSF in C57BL/6 murine thioglycolate-elicited peritoneal-derived macrophages, with and without pre-incubation with affinity purified goat anti-MIF-A3 IgG, using ELISA cytokine kit analysis. Results of this study suggest that anti-MIF-A3 IgG does not enhance clearance of Mav2, alter phagocytosis or alter phagosome-lysosome interactions as determined by electron microscopy in Mav2 infected macrophages. MIF-A3 does induce secretion of IL-6, but does not induce secretion of TNFalpha, IL-1beta, and GM-CSF. TNFalpha has been previously shown to reduce growth, while IL-6 has been shown to enhance growth of M. avium. Since IL-6 appears to enhance growth of M. avium and MIF-A3 induces IL-6 secretion, MIF-A3 may be responsible for enhanced intracellular growth in M. avium infections and be a factor in the pathogenesis of M. avium infections.

Intact autocrine activation and cytokine production by PMNs from injured adults with elevated Candida antigen titres

Injured patients with Candida antigen titres have increased mortality due to sepsis. Polymorphonuclear leucocytes (PMNs) from injured patients with elevated Candida antigen titres demonstrate impaired function against Candida albicans growth when compared with PMNs from injury matched controls. To determine if PMN dysfunction is global, PMNs from patients with positive Candida antigen titres were evaluated for their ability to activate the anticandidal function of normal PMNs (autocrine activation) and to produce tumour necrosis factor (TNF) and interleukin 8 (IL8), known activators of PMN anticandidal function, this study demonstrates that the PMN dysfunction is not global, as PMN cytokine production and autocrine activation remain intact.

Azole resistance in Candida

Resistance of Candida to azoles is an increasing problem. Susceptibility testing of Candida against fluconazole and ketoconazole is now feasible and desirable. Good correlation of resistance in vitro with clinical failure of fluconazole therapy has now been shown in mucosal candidiasis. The relationship, if any, between resistance and clinical failure in the context of invasive candidiasis is not clear at present and additional correlative work needs to be done. Monitoring of resistance trends in Candida is clearly important now.

Macrophage inhibitory factor-A3 derived from Mycobacterium avium serovar 2 inhibits candidacidal activity of murine peritoneal macrophages

Macrophage inhibitory factor-A3 (MIF-A3), a fraction derived from Mycobacterium avium serovar 2 inhibited candidacidal activity in macrophages from C57BL/6, C57BL/10, C3H/HeJ and A/J strains of mice. Inhibition of candidacidal activity was demonstrated at MIF-A3 concentrations ranging from 100-400 micrograms/ml in macrophages without additional stimulators (exception C3H/HeJ macrophages) and in macrophages additionally stimulated with 200 U/ml interferon-gamma, 100 ng/ml phorbol myristate acetate and 0.4 ng/ml E. coli lipopolysaccharide from all mouse strains tested. The decreased candidacidal effect produced by MIF-A3 was dose-dependent and appeared greatest in macrophages treated with phorbol myristate acetate and lipopolysaccharide. This effect was neutralized by the addition of goat anti-MIF-A3 antiserum. Macrophages from the Bcgs mouse strains (C57BL/6 and C57Bl/100 were more sensitive to the effect(s) of MIF-A3 than macrophages from the Bcgr mouse strains (C3H/HeJ and A/J).

Identification of an amphotericin B resistant strain of Candida albicans using a rapid 3H-glucose incorporation microassay

Using a 3H-glucose incorporation assay, antifungal sensitivity testing undertaken on an isolate of Candida albicans cultured from the blood of a bone marrow transplant patient documented resistance to amphotericin B but sensitivity to fluconazole and itraconazole. Information obtained from in vitro antifungal sensitivity testing can be used to direct in vivo antifungal therapy. Widespread application of standardized in vitro antifungal sensitivity testing is needed.

Protection of C3H/HE J mice from development of Candida albicans infection by oral administration of Juzen-taiho-to and its component, Ginseng radix: possible roles of macrophages in the host defense mechanisms

Protective effect of a Japanese traditional herbal medicine, Juzen-taiho-to (TJ-48), which was recently reported to augment host-mediated antifungal actions, in Candida albicans-infected mice was further studied. TJ-48, given orally once daily for 5 consecutive days in a dose of 2 g/kg after intravenous infection of C. albicans, prolonged survival period of infected mice of a C3H/He J strain which is characteristic of functional deficiency of macrophages, but did not that of infected mice of a C3H/He N strain with normal macrophage function. Peritoneal macrophages obtained from C3H/He J mice showed a moderate inhibitory activity against Candida growth in vitro. The anti-Candida activity of the macrophages was augmented by the addition of TJ-48 or some component extracts of TJ-48 to the incubation medium. Among such active component extracts is an extract of Ginseng radix which was demonstrated to enhance the anti-Candida activity of macrophages in vitro and to prolong the survival time of C. albicans-infected C3H/He J mice without effect on C3H/He N mice. On the base of these findings, the mechanisms underlying the protective action of TJ-48 against systemic Candida infection was discussed in relation with its possible activity to activate the macrophage function.

Suppression of anti-Candida activity of murine neutrophils by progesterone in vitro: a possible mechanism in pregnant women's vulnerability to vaginal candidiasis

Sex steroid hormones were examined for their effect on mycelial growth of Candida albicans, and the inhibitory activity of casein-induced murine peritoneal neutrophils against mycelial growth of C. albicans was examined in vitro using a crystal violet staining method or a [3H]glucose incorporation method. Four steroid hormones, danazol, estradiol, estriol and testosterone had no effect on mycelial growth of C. albicans, but progesterone appeared to convert the growth form of C. albicans from hyphal to yeast. Danazol (10(-6) M) and progesterone (10(-5) M) suppressed anti-Candida activity of neutrophils of non-treated mice, while testosterone, estradiol, and estriol did not. The anti-Candida activity of neutrophils of estradiol-pretreated mice was clearly suppressed by progesterone even at 10(-6) M which corresponded to its plasma concentration in pregnant women in the third trimester. The physiological significance of this suppressive effect of progesterone was discussed in relation to the vulnerability of pregnant women to vaginal candidiasis.

Suppression of anti-Candida activity of murine and human neutrophils by glucocorticoids

Effects of glucocorticoid (GC) compounds on inhibitory activity of neutrophils to mycelial growth of Candida albicans were examined by in vitro crystal violet staining method with 14 hr coculture. Both GC hormones (hydrocortisone > or = 6 x 10(-7) M and corticosterone > or = 10(-6)M) and anti-inflammatory GC agents (prednisolone > or = 10(-7) M and dexamethasone > or = 10(-8) M) significantly suppressed anti-Candida activity of murine casein-induced neutrophils. Anti-Candida activity of human neutrophils prepared from peripheral blood was also suppressed by hydrocortisone (> or = 6 x 10(-7) M). These GC compounds did not affect the Candida growth in the absence of neutrophils. Steroidal compounds without anti-inflammatory activity, cholesterol, cholic acid, aldosterone did not suppress neutrophil activity. These results suggest that GCs at their physiological or clinical concentration may suppress anti-Candida activity of neutrophils in vivo.

A rapid colorimetric assay for determination of leukocyte-mediated inhibition of mycelial growth of Candida albicans

A staining method with crystal violet (CV) was demonstrated to be useful for a simple, quick and objective assessment of in vitro growth inhibitory activity of leukocytes against Candida albicans cells. Candida cells incubated with murine neutrophils or macrophages for 14 hr in microwells were stained with CV and, after washing with 0.25% sodium dodecyl sulfate (SDS), treated with isopropanol containing HCl (0.04 N) to extract Candida cell-bound CV. Then the absorbance at 590 nm of the isopropanol extract was photometrically measured. The results showed that the photometrical absorbance was proportional to the amount of 3H-glucose taken up by C. albicans cells, which reflected the number of viable Candida cells.

Inhibition of Candida albicans growth by murine peritoneal neutrophils and augmentation of the inhibitory activity by bacterial lipopolysaccharide and cytokines

Anti-Candida activity of murine neutrophils and its regulation by immunomodulators were studied in vitro. Murine neutrophils which were prepared from peritoneal-exudated cells inhibited the growth of Candida albicans at an effector: target (E/T) ratio of 30/1 or above. This anti-Candida activity of neutrophils was augmented by lipopolysaccharide from Escherichia coli, murine tumor necrosis factor (TNF), murine interferon-gamma (IFN-gamma) and murine granulocyte macrophage colony-stimulating factor (GM-CSF) but not by granulocyte colony-stimulating factor (G-CSF) added to the incubation medium. Greater extent of augmentation was obtained when TNF plus GM-CSF or INF-gamma plus GM-CSF were used in combination. These results indicate that anti-Candida activity of murine neutrophils is regulated similarly to that of the human neutrophils reported previously. Therefore murine peritoneal neutrophils can be used as a favorable substitute for human neutrophils in studies on protective machinery against C. albicans infection.

Elevated Candida antigen titers are associated with neutrophil dysfunction after injury

This study was undertaken to determine if impaired neutrophil (polymorphonuclear leukocytes [PMNL]) function is associated with an elevated Candida antigen titer after injury. PMNL from eight severely injured adults with Candida antigen titers of > or = 1:4 (titer positive) were evaluated for the ability to inhibit growth of Candida albicans in vitro by using a [3H]glucose incorporation assay. PMNL from eight severely injured adults with titers of < 1:4 (titer negative) and from eight healthy volunteers were studied for comparison. PMNL from the titer-positive patients had suppressed ability to inhibit C. albicans growth compared with PMNL from titer-negative patients and healthy volunteers. In vitro, PMNL function against C. albicans could be augmented significantly by cytokines. Granulocyte macrophage-colony-stimulating factor was most potent at augmenting function, followed by interleukin-8 and gamma interferon. Injured patients with elevated candida antigen titers have impaired PMNL function against C. albicans, and this function can be restored by cytokines.

Antifungal susceptibility testing

Unlike antibacterial susceptibility testing, reliable antifungal susceptibility testing is still largely in its infancy. Many methods have been described, but they produce widely discrepant results unless such factors as pH, inoculum size, medium formulation, incubation time, and incubation temperature are carefully controlled. Even when laboratories agree upon a common method, interlaboratory agreement may be poor. As a result of numerous collaborative projects carried out both independently and under the aegis of the Subcommittee on Antifungal Susceptibility Testing of the National Committee for Clinical Laboratory Standards, the effects of varying these factors have been extensively studied and a standard method which minimizes interlaboratory variability during the testing of Candida spp. and Cryptococcus neoformans has been proposed. This review summarizes this work, reviews the strengths and weaknesses of the proposed susceptibility testing standard, and identifies directions for future work.

Quantitative measurement of lymphocyte mediated growth inhibition of Candida albicans

A rapid and reproducible assay has been developed to measure the capacity of lymphocytes to inhibit the growth of Candida albicans. Fungal growth inhibition was assessed optimally as the incorporation of [3H]uridine into preformed hyphae, following interaction of the hyphae with effector lymphocytes. The assay was sensitive to the detection of fungal growth inhibition by lymphocytes at low effector to target ratios and results correlated well with other methods for measurement of anti-C. albicans growth inhibition in vitro. Although the assay was developed for the measurement of lymphocyte mediated anti-fungal activity, other mammalian cell populations can be assayed for growth inhibition of C. albicans as well. The described assay utilizes the enzyme lyticase to reduce the surface binding of C. albicans. The use of this enzyme permits the efficient harvest of large numbers of experimental samples with a multiple automated sample harvester.

Granulocyte colony-stimulating factor potentiates anti-Candida albicans growth inhibitory activity of polymorphonuclear cells

Granulocyte colony-stimulating factor (G-CSF) stimulates a subset of granulocyte colony forming cells and when administered to neutropenic individuals results in recovery of blood neutrophil numbers to normal levels. Therefore, G-CSF may be a useful therapeutic agent for infections in immunocompromised hosts. However, to date there has been only limited information that G-CSF activates the antimicrobial activity of neutrophils. In the present study, we found that recombinant G-CSF promotes the anti-Candida albicans activity of normal human blood polymorphonuclear (PMN) cells in vitro using both a 3H-glucose uptake procedure and a Candida colony counting assay. As little as 0.1 ng/ml G-CSF induced significant anti-Candida activity in the PMN cultures. G-CSF treatment also enhanced superoxide anion production by the PMNs in response to f-MLP as determined by the superoxide dismutase inhibitable cytochrome C reduction method. Such results show that G-CSF can promote the antimicrobial activity of peripheral blood PMNs against C. albicans.

Anticandidal activity and interleukin-1 beta and interleukin-6 production by polymorphonuclear leukocytes are preserved in subjects with AIDS

Polymorphonuclear granulocytes (PMN; or neutrophils) from uninfected or human immunodeficiency virus-infected subjects were tested for their ability to inhibit growth of Candida albicans and produce interleukin-1 beta (IL-1 beta) and IL-6 in vitro. It was seen that PMN from AIDS (Centers for Disease Control stage IV) patients expressed equal if not greater anticandidal activity compared with the activity expressed by neutrophils from all other subjects examined. On exposure to granulocyte macrophage-colony-stimulating factor or to a mannoprotein constituent (MP-F2) from C. albicans itself, PMN from AIDS patients showed enhanced antifungal activity and production of remarkable quantities of IL-1 beta and IL-6. These findings suggest that the functional abilities of PMN to inhibit Candida growth and secrete relevant proinflammatory and immunomodulatory cytokines are intrinsically preserved in AIDS patients.

Lipopolysaccharide restores anti-Candida albicans growth inhibition activity of polymorphonuclear neutrophils from retrovirus-immunosuppressed mice

It has been documented that the immune function of leukocytes may be markedly suppressed after infection of mice with the murine retrovirus Friend leukemia virus (FLV). Antimicrobial activity of polymorphonuclear neutrophils (PMNs) against Candida albicans is impaired after retrovirus infection of mice, and this occurs as early as 3 days after infection of genetically susceptible BALB/c mice. By 2 weeks after infection, there was essentially very little growth inhibition of C. albicans by PMNs from the FLV-infected mice. However, when bacterial lipopolysaccharide (LPS), a known activator of macrophages and PMNs, was added to PMNs from the FLV-infected mice, anti-C. albicans activity was restored to normal levels. This restoration of anti-C. albicans activity of FLV-infected mouse PMNs was observed after stimulation with as little as 0.01 micrograms of LPS per ml. The data obtained show that the impaired antimicrobial function of PMNs from retrovirus-infected mice can be readily restored by a biological response modifier such as bacterial LPS.

Lactoferrin release and interleukin-1, interleukin-6, and tumor necrosis factor production by human polymorphonuclear cells stimulated by various lipopolysaccharides: relationship to growth inhibition of Candida albicans

Lipopolysaccharides (LPSs) from Escherichia coli, Serratia marcescens, and Salmonella typhimurium, at doses from 1 to 100 ng/ml, strongly enhanced growth inhibition of Candida albicans by human polymorphonuclear leukocytes (PMN) in vitro. Flow cytometry analysis demonstrated that LPS markedly augmented phagocytosis of Candida cells by increasing the number of yeasts ingested per neutrophil as well as the number of neutrophils capable of ingesting fungal cells. LPS activation caused augmented release of lactoferrin, an iron-binding protein which itself could inhibit the growth of C. albicans in vitro. Antibodies against lactoferrin effectively and specifically reduced the anti-C. albicans activity of both LPS-stimulated and unstimulated PMN. Northern (RNA blot) analysis showed enhanced production of mRNAs for interleukin-1 beta, tumor necrosis factor alpha, and interleukin-6 and in neutrophils within 1 h of stimulation with LPS. The cytokines were also detected in the supernatant of the activated PMN, and their synthesis was prevented by pretreatment of LPS-stimulated PMN with protein synthesis inhibitors, such as emetine and cycloheximide. These inhibitors, however, did not block either lactoferrin release or the anti-Candida activity of LPS-stimulated PMN. These results demonstrate the ability of various bacterial LPSs to augment neutrophil function against C. albicans and suggest that the release of a candidastatic, iron-binding protein, lactoferrin, may contribute to the antifungal effect of PMN. Moreover, the ability to produce cytokines upon stimulation by ubiquitous microbial products such as the endotoxins points to an extraphagocytic, immunomodulatory role of PMN during infection.

A rapid Candida albicans hyphal-form growth inhibition assay: determination of myelomonocytic-mediated antifungal activity

An in vitro microassay for the measurement of Candida albicans hyphal-form growth inhibition by myelomonocytic cells is described. The assay is rapid, easy-to-perform and objective. A Candida strain capable of in vitro dimorphic transition from yeast to hyphal form has been employed. The assay is based on the incorporation of 3H-glucose by the fungus, the effect being dependent upon the time of pulse, size of the inoculum and concentration of radiolabelled metabolite. In particular, C. albicans hyphal form, obtained by a 3 h incubation in vitro in the presence of 10% fetal calf serum, is co-incubated with the effector cells. A pulse with 3H-glucose in water is then performed and the radioactivity incorporated by the residual Candida is taken as an indication of hyphal growth. We found that polymorphonuclear cells, peritoneal macrophages and the cloned GG2EE macrophage cell line significantly inhibited hyphal growth, the effects being time and effector-to-target cell ratio dependent.

Effect of Friend leukemia virus infection on susceptibility to Candida albicans

Previous studies have demonstrated that Friend leukemia virus (FLV) induces a profound immunosuppression in susceptible mice. The studies described in this report indicate that mice infected with FLV have an increased susceptibility to subsequent infection with the opportunistic pathogen Candida albicans, as measured by increased numbers of C. albicans CFU in the kidneys of FLV-infected mice relative to uninfected controls. Experiments in which the NB-tropic and N-tropic strains of FLV were used suggest that virus replication or the resulting virus burden may be important in the observed increased susceptibility to C. albicans. Since neutrophils are believed to be important in the response of mice to systemic Candida infections, the effect of FLV infection on neutrophil candidacidal activity was investigated. The percentage of neutrophils present in unfractionated Proteose Peptone-elicited peritoneal exudates of mice infected with FLV for 14 days was significantly lower than in uninfected control mice or mice infected with FLV for 6 or 10 days. When neutrophils from FLV-infected and control mice were purified, adjusted to equal concentrations, and tested for in vitro candidacidal activity, neutrophils from mice infected with FLV for 14 days were deficient in their ability to kill C. albicans relative to normal controls and mice infected with FLV for 6 or 10 days. Addition of normal mouse serum increased killing in all groups but did not restore candidacidal activity of neutrophils from mice infected with FLV for 14 days to levels of control neutrophils or neutrophils from mice infected for 6 or 10 days with the virus. These results suggest a defect in neutrophil function, at the later stages of FLV infection, involving in vitro candidacidal activity. In addition, neutrophils from FLV-infected mice may be deficient in in vivo chemotactic activity. These defects in neutrophil function could account, at least in part, for the observed increased susceptibility of FLV-infected mice to C. albicans.

Effects of Histoplasma capsulatum on murine macrophage functions: inhibition of macrophage priming, oxidative burst, and antifungal activities

Histoplasma capsulatum yeast cells fail to trigger an oxidative burst response in normal murine macrophages. The results of this study, in which an in vitro assay of macrophage antifungal effects was used, extend these findings. During 18 h of incubation, unprimed elicited murine macrophages inhibited H. capsulatum growth only when macrophages were present in great excess. Gamma interferon (IFN-gamma)-primed macrophages showed enhanced fungal growth inhibition but a similar requirement for an excess of phagocytes. Macrophages containing heat-killed H. capsulatum exhibited diminished antifungal effects toward viable H. capsulatum and Saccharomyces cerevisiae cells. Parallel experiments showed no comparable effect of ingested latex particles on macrophage antifungal activity. Using chemiluminescence as a measure of the oxidative burst, we found that macrophages primed in vitro with IFN-gamma alone failed to exhibit a significant response to triggering by H. capsulatum yeast cells unless a second priming agent (tumor necrosis factor alpha or bacterial lipopolysaccharide) was added to IFN-gamma. Furthermore, macrophage priming with single agents was blocked by the prior ingestion of heat-killed H. capsulatum. These studies provide evidence that ingestion of H. capsulatum yeast cells can induce a prompt and enduring deactivation of murine macrophages.