Purification of a mannan from Candida albicans which activates serum complement

High levels of short-chain fatty acids secreted by Candida albicans hyphae induce neutrophil chemotaxis via free fatty acid receptor 2

Candida albicans belongs to our commensal mucosal flora and in immune-competent individuals in the absence of epithelial damage, this fungus is well tolerated and controlled by our immune defense. However, C. albicans is an opportunistic microorganism that can cause different forms of infections, ranging from superficial to life-threatening systemic infections. C. albicans is polymorphic and switches between different phenotypes (e.g. from yeast form to hyphal form). C. albicans hyphae are invasive and can grow into tissues to eventually reach circulation. During fungal infections, neutrophils in particular play a critical role for the defense, but how neutrophils are directed toward the invasive forms of fungi is less well understood. We set out to investigate possible neutrophil chemoattractants released by C. albicans into culture supernatants. We found that cell-free culture supernatants from the hyphal form of C. albicans induced both neutrophil chemotaxis and concomitant intracellular calcium transients. Size separation and hydrophobic sorting of supernatants indicated small hydrophilic factors as responsible for the activity. Further analysis showed that the culture supernatants contained high levels of short-chain fatty acids with higher levels from hyphae as compared to yeast. Short-chain fatty acids are known neutrophil chemoattractants acting via the neutrophil free fatty acid receptor 2. In line with this, the calcium signaling in neutrophils induced by hyphae culture supernatants was blocked by a free fatty acid receptor 2 antagonist and potently increased in the presence of a positive allosteric modulator. Our data imply that short-chain fatty acids may act as a recruitment signal whereby neutrophils can detect C. albicans hyphae.

Characterisation and immunomodulating activities of exo-polysaccharides from submerged cultivation of Hypsizigus marmoreus

Exo-polysaccharides were purified and characterized from the fermentation broth of Hypsizigus marmoreus, a popular edible mushroom consumed in Asia. Among them, B-I-I and B-II-I exhibited potent complement fixating activity, meanwhile, B-N-I, B-I-I, B-II-I and B-II-II exhibited significant macrophage stimulating activity. Molecular weights of the four exo-polysaccharides were determined to be 6.3, 120, 150 and 11 kDa respectively. Molecular characterisation showed that B-N-I is basically an α-1→4 glucan, with branches on C6; B-I-I is a heavily branched α-mannan with 1→2 linked main chain. B-II-I and B-II-II, have a backbone of rhamno-galacturonan with 1→2 linked l-rhamnose interspersed with 1→4 linked galacturonic acid. Structure-activity relationship analysis indicated that monosaccharide compositions, molecular weight, certain structural units (rhamno-galacturonan type I and arabinogalactan type II) are the principal factors responsible for potent complement fixating and macrophage-stimulating activities. Their immunomodulating activities may, at least partly, explain the health benefits of the mushroom.

Bacteria and endotoxin in meconium-stained amniotic fluid at term: could intra-amniotic infection cause meconium passage?

BACKGROUND

Meconium-stained amniotic fluid (MSAF) is a common occurrence among women in spontaneous labor at term, and has been associated with adverse outcomes in both mother and neonate. MSAF is a risk factor for microbial invasion of the amniotic cavity (MIAC) and preterm birth among women with preterm labor and intact membranes. We now report the frequency of MIAC and the presence of bacterial endotoxin in the amniotic fluid of patients with MSAF at term.

MATERIALS AND METHODS

We conducted a cross-sectional study including women in presumed preterm labor because of uncertain dates who underwent amniocentesis, and were later determined to be at term (n = 108). Patients were allocated into two groups: (1) MSAF (n = 66) and (2) clear amniotic fluid (n = 42). The presence of bacteria was determined by microbiologic techniques, and endotoxin was detected using the Limulus amebocyte lysate (LAL) gel clot assay. Statistical analyses were performed to test for normality and bivariate comparisons.

RESULTS

Bacteria were more frequently present in patients with MSAF compared to those with clear amniotic fluid [19.6% (13/66) versus 4.7% (2/42); p < 0.05]. The microorganisms were Gram-negative rods (n = 7), Ureaplasma urealyticum (n = 4), Gram-positive rods (n = 2) and Mycoplasma hominis (n = 1). The LAL gel clot assay was positive in 46.9% (31/66) of patients with MSAF, and in 4.7% (2/42) of those with clear amniotic fluid (p < 0.001). After heat treatment, the frequency of a positive LAL gel clot assay remained higher in the MSAF group [18.1% (12/66) versus 2.3% (1/42), p < 0.05]. Median amniotic fluid IL-6 concentration (ng/mL) was higher [1.3 (0.7-1.9) versus 0.6 (0.3-1.2), p = 0.04], and median amniotic fluid glucose concentration (mg/dL) was lower [6 (0-8.9) versus 9 (7.4-12.6), p < 0.001] in the MSAF group, than in those with clear amniotic fluid.

CONCLUSION

MSAF at term was associated with an increased incidence of MIAC. The index of suspicion for an infection-related process in postpartum women and their neonates should be increased in the presence of MSAF.

Carbohydrate-based immune adjuvants

The role for adjuvants in human vaccines has been a matter of vigorous scientific debate, with the field hindered by the fact that for over 80 years, aluminum salts were the only adjuvants approved for human use. To this day, alum-based adjuvants, alone or combined with additional immune activators, remain the only adjuvants approved for use in the USA. This situation has not been helped by the fact that the mechanism of action of most adjuvants has been poorly understood. A relative lack of resources and funding for adjuvant development has only helped to maintain alum's relative monopoly. To seriously challenge alum's supremacy a new adjuvant has many major hurdles to overcome, not least being alum's simplicity, tolerability, safety record and minimal cost. Carbohydrate structures play critical roles in immune system function and carbohydrates also have the virtue of a strong safety and tolerability record. A number of carbohydrate compounds from plant, bacterial, yeast and synthetic sources have emerged as promising vaccine adjuvant candidates. Carbohydrates are readily biodegradable and therefore unlikely to cause problems of long-term tissue deposits seen with alum adjuvants. Above all, the Holy Grail of human adjuvant development is to identify a compound that combines potent vaccine enhancement with maximum tolerability and safety. This has proved to be a tough challenge for many adjuvant contenders. Nevertheless, carbohydrate-based compounds have many favorable properties that could place them in a unique position to challenge alum's monopoly over human vaccine usage.

Macrophages in resistance to candidiasis

Candida albicans, an increasingly common opportunistic pathogenic fungus, frequently causes disease in immunodeficient but not immunocompetent hosts. Clarifying the role of the phagocytic cells that participate in resistance to candidiasis not only is basic to understanding how the host copes with this dimorphic pathogen but also will expedite the development of innovative prophylactic and therapeutic approaches for treating the multiple clinical presentations that candidiasis encompasses. In this review, we present evidence that a diverse population of mononuclear phagocytes, in different states of activation and differentiation and from a variety of host species, can phagocytize C. albicans blastoconidia via an array of opsonic and nonopsonic mechanisms and can kill C. albicans blastoconidia and hyphae by means of oxygen-dependent and -independent mechanisms. Reactive nitrogen intermediates should now be added to the well-established candidacidal reactive oxygen intermediates of macrophages. Furthermore, what were thought to be two independent pathways, i.e., nitric oxide and superoxide anion, have now been shown to combine to form a potent macrophage candidacidal molecule, peroxynitrite. In contrast to monocytes and neutrophils, which are important in resistance to early stages of C. albicans infections, more differentiated macrophages activated by cytokines such as gamma interferon participate in the acquired resistance of hosts with C. albicans-specific, cell-mediated immunity. Evidence presented in this review demonstrates that mononuclear phagocytes, in some instances in the absence of other professional phagocytes such as neutrophils, play an import role in resistance to systemic and mucosal candidiasis.

(1-->3)-beta-D-glucan in culture fluid of fungi activates factor G, a limulus coagulation factor

Two well-known polysaccharides, (1-->3)-beta-D-glucan and mannan, are major structural components of the fungus cell wall. The G test is a direct method to measure (1-->3)-beta-D-glucan using a (1-->3)-beta-D-glucan-sensitive component, factor G, fractionated from the limulus lysate. The concentration of (1-->3)-beta-D-glucan in culture supernatants of Candida albicans increased to 1,390.0 pg/ml at 24 hours. The concentration of mannan also increased parallel with fungal growth. However, after digestion of supernatants with endo-(1-->3)-beta-D-glucanase, the reactivity to factor G disappeared, although titers of antimannan monoclonal antibody-based latex agglutination were unchanged. Our study demonstrated that cell suspensions of both C. albicans and Cryptoccocus neoformans activated the limulus factor G, and that not only the conidia form but also the filamentous form of Aspergillus fumigatus reacted with factor G. Various Candida spp. (C. paraspilosis, C. glabrata, C. tropicalis, C. krusei), Saccharomyces cerevisiae, Rhodotorula rubra, Trichosporon beigelii, and A. fumigatus released soluble (1-->3)-beta-D-glucan into their culture supernatants, but C. neoformans and Cunninghamella bertholletiae showed only a small reaction to the G test during their culture. Our results indicate that the G test is a good method for serodiagnosis of deep mycosis and also as a screening tool for contamination of medical devices, drugs, and experimental materials with (1 --> 3)-beta-D-glucan.

[Systemic candidiasis]

Candida proliferate within the body of patients with deficient cellular immunity either by the haematogenous route or by adjacency. This condition is often found in hospital patients. It explains the increasing incidence of disseminated candidiasis. They are preferentially found in patients who have had complicated surgery, mostly of the gastrointestinal tract and the heart, or transplant surgery (except for kidney transplants), or who have had prolonged intensive care. Other patients concerned are neonates with a low birth weight, haemato-oncology patients, heroin addicts and AIDS patients. Clinical signs are usually unspecific. When there is widespread involvement, clinical signs can be defined by the secondary locations, especially within the kidneys, lung, endocardium and brain in surgical patients, and liver and spleen in haemato-oncology patients. Eye, skin, gastrointestinal tract, and indeed, muscle lesions which are easily accessible, should be looked for routinely. This helps to ascertain the diagnosis, by showing the presence of Candida in the tissues. Moreover, isolating Candida from places which are normally sterile confirms deep-seated candidiasis. However, the presence of Candida in urine, bronchi, or drainage fluids is only the witness of saprophytism. This underlines the usefulness of immunological tests, which should soon benefit from the availability of new kits for the detection of cytoplasmic antigens. Indeed, the search for antibodies or circulating metabolites do not provide, at present, significantly different results in patients who have only been colonised and in those who have a systemic candidiasis. Interesting results are only obtained by showing the presence of mannans, in research laboratories. For treatment, amphotericin B remains the standard antifungal agent, and the association of amphotericin B with flucytosine the recommended association. However, drugs such as the new triazoles, among which fluconazole is particularly well tolerated and efficient, may considerably alter the principles of treatment. Finally, combining a fungal decontamination of the gut should help reduce the very high death rate of systemic candidiasis.

Candida cell wall mannan in the vagina and its association with the signs and symptoms of vaginal candidosis

Measurement of Candida cell wall polysaccharide (mannan) with an enzyme-linked immunosorbent assay (ELISA) was evaluated as an alternative to viable counting for the enumeration of yeast cell numbers in the human vagina. A statistically significant association was found between mannan levels and the number of colony forming units in vaginal washings collected from 40 women infected with Candida albicans (r = 0.81), indicating the accuracy of mannan levels in reflecting yeast cell load in vulvo-vaginal candidosis. Subsequent comparisons revealed a significant association between mannan levels and clinical signs in the vagina, so reflecting the importance of vulvitis and vaginitis as clinical markers for determining the severity of infection. No association was found between yeast load and the clinical symptoms, indicating the high degree of patient subjectivity. Estimation of mannan levels could be developed and used for the rapid laboratory investigation of chronic vulvo-vaginal candidosis.

Glycosidic activities of Candida albicans after action of vegetable latex saps (natural antifungals) and isoconazole (synthetic antifungal)

Glycosidic activities have been examined in Candida albicans grown on medium culture containing latex sap (natural antifungal) or isoconazole (synthetic antifungal). The different types of utilized latex sap were those of Lactuca sativa (latex exuded from articulated laticifers) and Asclepias curassavica (latex flowing from non-articulated laticifers). The same enzyme assays were performed on C. albicans grown without antifungal compounds. Except for alpha-arabinosidase, all glycosidase activities were increased when C. albicans was grown in medium supplemented with L. sativa latex sap. The most stimulated activities were those of beta-fucosidase, alpha-galactosidase, alpha- and beta-glucosidase, alpha- and beta-mannosidase, acetyl-beta-glucosaminidase. The presence of A. curassavica latex sap in culture medium produced similar results: the most stimulated activities were those of alpha-mannosidase, alpha-galactosidase, acetyl-beta-glucosaminidase and beta-fucosidase. Electron microscope observations suggested a correlation between this stimulation of glycosidic activities and the fungal cell wall breakdown. For comparison the presence of isoconazole in culture medium yields no increase in glycosidic activities and no ultrastructural modification of fungal cell wall. The mode of action of latex saps in cell wall breakdown is discussed.

Serum-independent neutrophil chemotaxins in the yeast phase of Candida albicans

Cell extracts from 6 strains of Candida albicans grown under different conditions were partially purified and tested for inherent chemotactic activity for human polymorphonuclear granulocytes. Chemotactic activity was demonstrated in the absence of serum using the Boyden chamber technique. No chemokinetic effects of the extracts examined were found using the same method. Cross desensitization experiments of PMN with C. albicans extracts and known leukotaxins (PAF, LTB4, and FMLP) revealed that C. albicans-derived chemotaxins differed from the known chemoattractants. Their possible role in Candida infections is discussed.

Candida cell wall mannan: a polysaccharide with diverse immunologic properties

It is clear that mannan has the potential to influence multiple biologic functions in vivo and in vitro, including both mannan-specific and mannan-nonspecific activities. Based on in vitro studies, various mechanisms have been proposed for the regulatory activities observed, ranging from interference with normal PMNL and monocyte function to the induction of T suppressor cells. It may well be, in fact, that different mechanisms function at different levels depending upon the specific phenomenon being influenced. Approaches to determining the mechanisms involved in these regulatory phenomena, however, have been complicated by the fact that many studies were performed with mannan extracted in the laboratory by traditional methods and used as such without further purification. Most laboratory-acquired mannans appear to be heterogeneous mixtures containing polymers of differing size and charge. When such mixtures have been separated on the basis of size or charge, it has been shown that biologic function can be correlated with individual fractions, and that a single bulk preparation of mannan can contain components with opposing biologic activities. Resolution of the specific mechanisms involved in the regulatory phenomena described, therefore, will not be complete until homogeneous preparations of mannan are employed to investigate the mechanisms.

Infection and labor: the detection of endotoxin in amniotic fluid

Intra-amniotic infections are frequently caused by gram-negative organisms. Lipopolysaccharide, or endotoxin, is a component of the cell wall of these bacteria. The Limulus amebocyte lysate assay is the most sensitive test clinically available for the detection of endotoxin in biologic samples. The diagnostic value of the Limulus amebocyte lysate assay test for the detection of intra-amniotic infection has been examined and compared with that of the Gram stain. The Gram stain had a 60.8% sensitivity and 9.6% false positive rate. The Limulus amebocyte lysate assay had a 69% sensitivity and a 4.8% false positive rate. When both tests were used in combination, the sensitivity improved to 95.6%, whereas the false positive rate was 14.3%. The Limulus amebocyte lysate assay test is a rapid, sensitive, inexpensive, and simple test for the detection of gram-negative intra-amniotic infections.

Activation and binding of C3 by Candida albicans

Interaction with components of the complement system is an important aspect of the pathogenesis of infection by Candida albicans. The key role of C3 as an opsonic ligand and as an element in amplification of complement activation led us to examine several factors that influence the activation and binding of C3 cleavage fragments to the yeast. Activation and binding of C3 were determined by use of normal human serum containing 125I-labeled C3. Incubation of yeast-phase cells in 20% serum led to deposition of 2.5 X 10(5) to 3.0 X 10(5) molecules of C3 per yeast cell. Binding of C3 was absent in serum that was heat inactivated for 30 min at 37 degrees C or in serum that was chelated with EDTA. Chelation of serum with EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] reduced binding of C3 fragments by 31%. These results suggest that the alternative complement pathway is the primary mechanism for activation and binding of C3 fragments to C. albicans. Bound C3 could be partially removed (50%) by treatment with 1.0 M hydroxylamine. In contrast, 1.0 M hydroxylamine removed 98% of the C3 fragments bound to encapsulated Cryptococcus neoformans. These results suggest that ester bonds are the primary mechanism for binding C3 to C. neoformans, whereas binding of C3 to C. albicans involves both ester and amide bonds. Monoclonal antibodies specific for C3c and an iC3b neoantigen were used to identify the fragment of C3 that was bound to C. albicans. The results showed that the primary fragment bound to the yeast was C3b. An examination of the kinetics of activation and binding of C3 fragments showed that activation and binding were very rapid. Near-maximal binding occurred after a 2.5- to 5-min incubation period. In contrast, activation and binding of C3 fragments to C. neoformans proceeded at a slower rate, with maximal binding requiring 10 to 20 min. These results indicate that activation and binding of C3 fragments by the yeasts C. albicans and C. neoformans differ in several important characteristics.

Innate and acquired immune responses against Candida albicans in congenic B10.D2 mice with deficiency of the C5 complement component

Congenic mice, sufficient or deficient with respect to the C5 component of complement, were evaluated for their innate and acquired immune responses to Candida albicans. When unimmunized mice were challenged intravenously and sacrificed at intervals for cultural analyses of kidneys, it was clear that C5-sufficient mice were able to deal more effectively with C. albicans during the first week after challenge than C5-deficient mice. When immunized mice were challenged intravenously to assess the development of protective responses, an intact complement cascade appeared to contribute to the more rapid clearance of fungi during the first few weeks following challenge, but by the fourth week after challenge, the numbers of fungi had decreased significantly in both types of mice and were at levels which were not significantly different. No significant differences were detected in the development of delayed hypersensitivity or Candida-specific antibody between C5-sufficient and C5-deficient mice either. C5-deficient mice did have slightly elevated levels over the C5+ mice, but this may simply reflect the prolonged antigenic load during the first 3 weeks following intravenous challenge in both immune and nonimmune animals. The later-acting complement components, while appearing to contribute to the early inhibition of the growth of C. albicans in the nonimmune animal, had no adverse effect on the development of specific immune responses, in that delayed hypersensitive responses were equivalent between the two groups, antibody response was not significantly altered and the ultimate outcome of challenge in immunized animals was not affected.

Adherence of Candida species to human epidermal corneocytes and buccal mucosal cells: correlation with cutaneous pathogenicity

Adherence of microorganisms to epidermal corneocytes may be a prerequisite for cutaneous colonization and infection. Six species of Candida were assayed in vitro for adherence to human epidermal corneocytes and buccal mucosal cells, and compared to previous studies of pathogenicity in a rodent model of cutaneous candidiasis. C. albicans and C. stellatoidea exhibited marked adherence to both epithelial cell types over time, and were cutaneous pathogens in the rodent model. The remaining species showed little or no adherence, and were nonpathogenic to skin. Adherence to corneocytes was not inhibited by ethylenediamine tetraacetic acid, mannan polysaccharide, or concanavalin A lectin. Fresh human serum, but not heat-inactivated serum, inhibited C. albicans adherence by 50%, and was associated with the deposition of complement components, C3 and factor B on blastospores. Adherence to epithelial corneocytes and mucosal cells is a property of pathogenic species of Candida, and may participate in cutaneous colonization and infection mechanisms. Adherence was time-dependent, and did not require divalent cations. Cell wall mannan may participate in the "adhesin" complex. Mannan activation of serum complement and deposition of C3 and factor B on blastospores may provide a protective action by inhibiting Candida adherence to corneocytes.

Immune responses to Candida albicans in genetically distinct mice

Mice from six genetically distinct strains were examined for their immune responses to Candida albicans in in vitro and in vivo assays, and naive mice and mice immunized with the fungus were challenged intravenously with three different doses of C. albicans to determine differences in susceptibility. Naive mice from the six groups showed substantial differences in resistance to challenge based on mortalities and quantitative cultures of kidneys, with mice from strains C57BL/6J and BALB/cByJ showing the most resistance; mice from strains A/J, C3H/HeJ, and CBA/J showing moderate susceptibility; and mice from strain DBA/2J showing the highest degree of susceptibility to challenge. Unimmunized mice from strains C57BL/6J and BALB/cByJ did not produce detectable levels of Candida-specific antibody by the end of the 28-day observation period when challenged intravenously, but the other strains did. Immunized mice showed a degree of protection to challenge, with all groups except mice from strain BALB/cByJ showing a reduction of two to three log units in the level of colonization in their kidneys and all strains producing significant levels of antibody. Additionally, the immunized mice of all strains developed substantial levels of delayed-type hypersensitivity and demonstrated nearly identical lymphocyte proliferative responses to Candida antigens. The results indicate that resistance to systemic candidiasis is dependent upon a combination of innate factors, predominately an intact complement system, and the acquisition of an immune response, most likely of a cell-mediated type. Additionally, the findings suggest that genetic control of acquired resistance to C. albicans may not be associated with the H-2 complex.

The fate of experimental cutaneous candidiasis in guinea pigs under the suppressed polymorphonuclear leukocyte chemotaxis by colchicine

Experimental cutaneous Candida albicans infections in guinea pigs are histologically characterized by intense epidermal polymorphonuclear leukocyte (PMN) accumulation. To study the role of PMNs in vivo, we injected 250 microgcolchicine/kg i.p., a strong inhibitor of PMN chemotaxis, and observed the influence of reduced PMN migration in experimental cutaneous candidiasis with special interest in the elimination course of the organisms. There was a significant delay in the clearance of the organisms in the colchicine-treated group with decreased epidermal PMN infiltration and prolonged visible scaling process. Our data suggest that the delay of epidermal PMN migration parallels the disappearance of the organisms from the infected skin and that PMNs play an important part in defense against candida infections especially in the elimination process.

Analysis of an in vivo model to study the interaction of host factors with Candida albicans

Conditions were established under which membrane diffusion chambers surgically implanted into mice could be used to study interactions between host defense factors and Candida albicans within the chambers. Depending on the size of membrane pores, soluble host substances and phagocytic cells entered the chambers during the first 24 h after chamber implantation. By 7 days in vivo, the membranes of chambers appeared impermeable to these host factors. Mouse phagocytic cells were found to be functional within the in vivo chambers whether the cells emigrated to the chambers on their own accord or were placed there before chamber implantation. Opsonic factors such as antibody and complement appeared to be biologically functional within the in vivo chambers. Conditions suitable for harvesting C. albicans from the chambers also were determined.

Effect of topical applications of heavy suspensions of killed Malassezia ovalis on rabbit skin

Heavy applications of suspensions of killed Malassezia ovalis on rabbit skin produced lesions that both grossly and microscopically resembled human psoriasis. This system may afford not only a model but also an explanation for that disease.