What's new in the mechanisms of host resistance to Candida albicans infection?

Identification, quantification and bioinformatic analysis of RNA-dependent proteins by RNase treatment and density gradient ultracentrifugation using R-DeeP

Analysis of RNA-protein complexes is central to understanding the molecular circuitry governing cellular processes. In recent years, several proteome-wide studies have been dedicated to the identification of RNA-binding proteins. Here, we describe in detail R-DeeP, an approach built on RNA dependence, defined as the ability of a protein to engage in protein complexes only in the presence of RNA, involving direct or indirect interaction with RNA. This approach provides-for the first time, to our knowledge-quantitative information on the fraction of a protein associated with RNA-protein complexes. R-DeeP is independent of any potentially biased purification procedures. It is based on cellular lysate fractionation by density gradient ultracentrifugation and subsequent analysis by proteome-wide mass spectrometry (MS) or individual western blotting. The comparison of lysates with and without previous RNase treatment enables the identification of differences in the apparent molecular weight and, hence, the size of the complexes. In combination with information from databases of protein-protein complexes, R-DeeP facilitates the computational reconstruction of protein complexes from proteins migrating in the same fraction. In addition, we developed a pipeline for the statistical analysis of the MS dataset to automatically identify RNA-dependent proteins (proteins whose interactome depends on RNA). With this protocol, the individual analysis of proteins of interest by western blotting can be completed within 1-2 weeks. For proteome-wide studies, additional time is needed for the integration of the proteomic and statistical analyses. In the future, R-DeeP can be extended to other fractionation techniques, such as chromatography.

Candida albicans-conditioned medium protects yeast cells from oxidative stress: a possible link between quorum sensing and oxidative stress resistance

Candida albicans, the most frequent fungal pathogen of humans, encounters high levels of oxidants following ingestion by professional phagocytes and through contact with hydrogen peroxide-producing bacteria. In this study, we provide evidence that C. albicans is able to coordinately regulate the oxidative stress response at the global cell population level by releasing protective molecules into the surrounding medium. We demonstrate that conditioned medium, which is defined as a filter-sterilized supernatant from a C. albicans stationary-phase culture, is able to protect yeast cells from both hydrogen peroxide and superoxide anion-generating agents. Exponential-phase yeast cells preexposed to conditioned medium were able to survive levels of oxidative stress that would normally kill actively growing yeast cells. Heat treatment, digestion with proteinase K, pH adjustment, or the addition of the oxidant scavenger alpha-tocopherol did not alter the ability of conditioned medium to induce a protective response. Farnesol, a heat-stable quorum-sensing molecule (QSM) that is insensitive to proteolytic enzymes and is unaffected by pH extremes, is partly responsible for this protective response. In contrast, the QSM tyrosol did not alter the sensitivity of C. albicans cells to oxidants. Relative reverse transcription-PCR analysis indicates that Candida-conditioned growth medium induces the expression of CAT1, SOD1, SOD2, and SOD4, suggesting that protection may be mediated through the transcriptional regulation of antioxidant-encoding genes. Together, these data suggest a link between the quorum-sensing molecule farnesol and the oxidative stress response in C. albicans.

Homology, disruption and phenotypic analysis of CaGS Candida albicans gene induced during macrophage infection

During macrophage infection Candida albicans expresses differentially several genes whose functions are associated with its survival strategy. Among others, we have isolated CaGS gene, which is homologous to SNF3, a glucose sensor of Saccharomyces cerevisiae. To elucidate its potential role during infection, CaGS has been disrupted and the resulting phenotype analyzed on different solid media. The null mutant lost the ability to form hyphae on a medium with low glucose concentration and serum. Furthermore, this mutant does not disrupt macrophage in in vitro infections. We believe that this putative glucose sensor is involved in hyphal development during macrophage infection.

Susceptibility of germfree phagocyte oxidase- and nitric oxide synthase 2-deficient mice, defective in the production of reactive metabolites of both oxygen and nitrogen, to mucosal and systemic candidiasis of endogenous origin

Mice deficient for phagocyte oxidase (Phox) and nitric oxide synthase 2 (NOS2) (gp91phox-/-/NOS2-/-), defective in the production of both reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI), were used to investigate the role of phagocytic cells during mucosal and systemic candidiasis of endogenous origin. The alimentary tracts of germfree mice were colonized with Candida albicans wild type or each of two hyphal signaling-defective mutants (efg1/efg1 and efg1/efg1 cph1/cph1). All Candida-colonized gp91phox-/-/NOS2-/- mice were moribund within 12 to 15 days after oral inoculation. C. albicans wild-type and mutant strains colonized the alimentary tracts equally well and were able to translocate, most likely via Peyer's patches and mesenteric lymph nodes, to the internal organs and trigger the formation of abscesses; however, the wild-type and mutant strains did not survive in the abscessed murine tissues. Surprisingly, there was no significant difference in the ability of peritoneal exudate cells from gp91phox-/-/NOS2-/-, NOS2-/-, gp91phox-/-, or immunocompetent C57BL/6 mice to kill C. albicans in vitro. This suggests that anti-Candida factors other than ROI and RNI can control the growth of C. albicans and that gp91phox-/-/NOS2-/- mice die due to the inability of the host to control its inflammatory response to Candida. Correspondingly, reverse transcription-PCR analysis showed increased expression of the cytokines gamma interferon, tumor necrosis factor alpha, and the chemokines MIP-2 and KC at the site of infection, while interleukin-15 expression remained relatively unchanged between germfree and infected tissues. These studies indicate that defects in ROI and RNI enabled C. albicans to translocate and disseminate to the internal organs, resulting in an uncontrolled immune response, severe pathology, and death; however, ROI and RNI were not required for the killing of phagocytized C. albicans, indicating that other anti-Candida factors either compensate or are sufficient for the killing of phagocytized Candida.

Genetic analysis of innate immunity in resistance to Candida albicans

Systemic candidiasis is a significant cause of nosocomial infections and the mechanisms of defense against Candida albicans in humans remain poorly understood. Studies in animal models have demonstrated the importance of innate immunity in controlling the response to infection. Although Th1 cytokines have been shown to direct the overall outcome of infection, the precise role of the Th1/Th2 response and, more generally, the adaptive immune response as a whole, in systemic candidiasis, appears to apply mainly to the development of resistance to reinfection. A genetic approach to the identification of host factors regulating pathogenesis and susceptibility to C. albicans infection has been used in humans and in mouse models of infection. Mouse mutants bearing experimentally induced mutations in specific genes have provided a systematic tool for directly assessing the role of individual proteins in C. albicans susceptibility. Inbred mouse strains have been valuable in showcasing the spectrum of naturally occurring variations in initial susceptibility to infection, and type of disease developed. Crosses between resistant and susceptible strains have led to the detection of additional gene effects affecting innate immunity. Of particular interest is the major effect of a naturally occurring loss-of-function mutation in the C5 complement component that has become fixed in many inbred strains. These and other studies have shown that both a functional complement pathway and robust inflammatory response are critical for resistance to C. albicans.

Genes involved in beta-oxidation, energy metabolism and glyoxylate cycle are induced by Candida albicans during macrophage infection

The ability of intracellular pathogens to cause infection is related to their capacity to survive and grow inside macrophages or in other cell types. Candida albicans latent virulence is likely to be related to a similar mechanism of avoiding killing by specialized cells and to the resulting ability to grow in such hostile environments. Using a differential display reverse transcription polymerase chain reaction technique, we have identified seven genes induced in C. albicans during macrophage phagocytosis. Sequence analyses and database searches revealed that these cDNAs coded for proteins homologous to yeast metabolic proteins. Interestingly, four of them are putative peroxisomal proteins, and two are involved in environmental signal sensing and transduction. Among the seven genes induced by C. albicans, six represent new information that were not described in other infection models.

Experimental oral candidiasis in animal models

Oral candidiasis is as much the final outcome of the vulnerability of the host as of the virulence of the invading organism. We review here the extensive literature on animal experiments mainly appertaining to the host predisposing factors that initiate and perpetuate these infections. The monkey, rat, and mouse are the choice models for investigating oral candidiasis, but comparisons between the same or different models appear difficult, because of variables such as the study design, the number of animals used, their diet, the differences in Candida strains, and the duration of the studies. These variables notwithstanding, the following could be concluded. (i) The primate model is ideal for investigating Candida-associated denture stomatitis since both erythematous and pseudomembranous lesions have been produced in monkeys with prosthetic plates; they are, however, expensive and difficult to obtain and maintain. (ii) The rat model (both Sprague-Dawley and Wistar) is well proven for observing chronic oral candidal colonization and infection, due to the ease of breeding and handling and their ready availability. (iii) Mice are similar, but in addition there are well characterized variants simulating immunologic and genetic abnormalities (e.g., athymic, euthymic, murine-acquired immune deficiency syndrome, and severe combined immunodeficient models) and hence are used for short-term studies relating the host immune response and oral candidiasis. Nonetheless, an ideal, relatively inexpensive model representative of the human oral environment in ecological and microbiological terms is yet to be described. Until such a model is developed, researchers should pay attention to standardization of the experimental protocols described here to obtain broadly comparable and meaningful data.

Flow cytometric quantitation of phagocytosis in heparinized complete blood with latex particles and Candida albicans

We report a rapid method for the flow cytometric quantitation of phagocytosis in heparinized complete peripheral blood (HCPB), using commercially available phycoerythrin-conjugated latex particles of 1 micron diameter. The method is faster and shows greater reproducibility than Bjerknes' (1984) standard technique using propidium iodide-stained Candida albicans, conventionally applied to the leukocytic layer of peripheral blood but here modified for HCPB. We also report a modification of Bjerknes' Intracellular Killing Test to allow its application to HCPB.

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.

Kinetics of anti-mannan antibodies useful in confirming invasive candidiasis in immunocompromised patients

In studying the anti-mannan antibodies longitudinally in serial serum samples of three immunocompromised patients, it was observed that anti-mannan antibodies started to increase shortly after the moment that cultures of deep-tissue sites became positive with Candida albicans. The mean anti-mannan antibody titers determined in a group of 36 immunocompromised patients with invasive candidiasis increased within two weeks after the probable onset of invasive candidiasis. In contrast, anti-mannan antibody levels in serial serum samples of 14 immunocompromised patients who were only colonized with C. albicans remained stable or decreased over time. The HA test measuring the anti-mannan antibodies was 64% sensitive and 89% specific in determining invasive candidiasis. In contrast, antibodies specific for candidal cytoplasmic antigens or enolase alone were of little value in confirming invasive candidiasis in these immunocompromised patients.

Acute labyrinthitis associated with systemic Candida albicans infection in ageing mice

The yeast Candida albicans is an important opportunistic pathogen that has been associated with disease of the inner ear. This study describes the histopathology of acute labyrinthitis caused by systemic infection with C. albicans in aging inbred mice. Within four days after infection, yeast and hyphal forms of C.albicans were found in the membranous labyrinth. The utricle and the adjacent parts of the ampullary regions of the semicircular canals were most severely affected, but damage was also seen in the scala media, the scala tympani, the saccule, and the scala vestibuli. In the utricle, the lining epithelium of the membranous labyrinth was disrupted, and the lining cells of the vestibular membrane showed foci in which the membrane was disrupted. The data suggest that age may represent a risk factor for fungal labyrinthitis.

Production and function of cytokines in natural and acquired immunity to Candida albicans infection

Host resistance against infections caused by the yeast Candida albicans is mediated predominantly by polymorphonuclear leukocytes and macrophages. Antigens of Candida stimulate lymphocyte proliferation and cytokine synthesis, and in both humans and mice, these cytokines enhance the candidacidal functions of the phagocytic cells. In systemic candidiasis in mice, cytokine production has been found to be a function of the CD4+ T helper (Th) cells. The Th1 subset of these cells, characterized by the production of gamma interferon and interleukin-2, is associated with macrophage activation and enhanced resistance against reinfection, whereas the Th2 subset, which produces interleukins-4, -6, and -10, is linked to the development of chronic disease. However, other models have generated divergent data. Mucosal infection generally elicits Th1-type cytokine responses and protection from systemic challenge, and identification of cytokine mRNA present in infected tissues of mice that develop mild or severe lesions does not show pure Th1- or Th2-type responses. Furthermore, antigens of C. albicans, mannan in particular, can induce suppressor cells that modulate both specific and nonspecific cellular and humoral immune responses, and there is an emerging body of evidence that molecular mimicry may affect the efficiency of anti-Candida responses within defined genetic contexts.

T helper cell dichotomy to Candida albicans: implications for pathology, therapy, and vaccine design

Acquired immunity to Candida albicans is believed to prevent mucosal colonization of adult immunocompetent individuals from progressing to symptomatic infection. Resistance to disease appears to correlate with the detection of delayed-type hypersensitivity responses in vivo and a T helper type 1 (Th1) cytokine secretion profile in vitro. Cellular immunodeficiency, particularly HIV infection, greatly increases the risk of mucosal infection, confirming that CD(4+)-cell-directed immunity is effective locally in controlling infectivity of the yeast. While Th1-type CD4+ cell activation resulting in phagocyte-dependent immunity clearly represents an important mechanism of anticandidal resistance, clinical observations suggest that Th2-type CD4+ cell reactivity may be triggered by Candida antigens in several disease states, including symptomatic infections and immunopathology. This may imply that a Th1-type pattern of reactivity characterizes the saprophytic yeast carriage and resistance to disease by healthy humans, whereas Th2-type responses would be mostly associated with pathology. Moreover, Candida-specific T helper responses, namely humoral and cell-mediated immunity, appear to be reciprocally regulated, as typically occurs in experimental models of parasitic and retroviral infection, where the Th1/Th2 paradigm of acquired immunity has been best characterized. Recent studies, besides providing direct evidence for the occurrence of cross-regulatory Th1 and Th2 responses in mice with candidiasis, emphasize the potential of cytokine/anticytokine therapy for recruiting Candida-specific responses toward protective, Th1-type CD4+ cell reactivity. At the same time, these studies call attention to the possible consequences of C. albicans infection for immunopathology, allergy, and coinfection.

A TH1-TH2-like switch in candidiasis: new perspectives for therapy

An imbalance in TH1-type and TH2-type responses may allow Candida albicans to modify the host response to favor its own persistence. This hypothesis has important consequences for allergy, autoimmunity and co-infection, and also highlights a potential role for cytokine and anti-cytokine therapy in Candida-related pathology.

Tolerance to staphylococcal enterotoxin B initiated Th1 cell differentiation in mice infected with Candida albicans

Staphylococcal enterotoxin B (SEB) is a bacterial superantigen that specifically activates T cells bearing V beta 8 T-cell receptor domains, which eventually leads to a long-lasting state of clonal anergy accompanied by selective cell death in the targeted CD4+ subset. Because the superantigen is known to promote Th1 cell differentiation in vitro, we have investigated the effect of SEB treatment on the course of Th2-associated progressive disease in mice infected systemically with Candida albicans. On the basis of the kinetics of SEB-induced changes in CD4+ cells and production in sera of interleukin 4 (IL-4), IL-10, and gamma interferon, we obtained evidence that V beta 8+ cell anergy concomitant with infection abolished the early IL-4/IL-10 response of the host to the yeast, ultimately leading to a state of resistance characterized by gamma interferon secretion in vitro by antigen-specific CD4+ cells. In contrast, SEB administered near the time of challenge resulted in accelerated mortality. Significant resistance to infection was also afforded by exposure of mice to a retrovirally encoded endogenous superantigen. These data suggest that CD4+ V beta 8+ T cells play an important role in vivo in the initiation of a Th2 response to C. albicans and that suppression of their activity may alter the qualitative development of the T-cell response and the outcome of infection.

Candida and oral candidosis: a review

Candida species are the most common fungal pathogens isolated from the oral cavity. Their oral existence both as a commensal and an opportunist pathogen has intrigued clinicians and scientists for many decades, and recent investigations have revealed many attributes of this fungus contributing to its pathogenicity. In addition, the advent of the human immunodeficiency virus infection and AIDS has resulted in a resurgence of oral Candida infections. Clinicians are witnessing not only classic forms of the diseases but also newer clinical variants such as erythematous candidosis, rarely described hithertofore. Therefore, this review is an attempt at detailing the current knowledge on Candida and oral candidoses together with the newer therapeutic regimes employed in treating these mycoses.

Cytokine gene expression in human peripheral blood mononuclear cells stimulated by mannoprotein constituents from Candida albicans

The expression of cytokine genes in cultures of human peripheral blood mononuclear cells (PBMC) stimulated with mannoprotein constituents (MP) of Candida albicans has been studied by means of S1 nuclease mapping analysis, polymerase chain reaction, and enzyme-linked immunosorbent assay. MP induced early, consistent, and long-lasting production of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha, and IL-6 mRNAs. Similar results were obtained when the same PBMC cultures were stimulated with the purified protein derivative (PPD) from Mycobacterium tuberculosis or with IL-2, although lower levels of IL-6 mRNA were detected in IL-2-stimulated cells than in MP- or PPD-stimulated cells. MP, PPD, and IL-2 induced appreciable levels of granulocyte-macrophage colony-stimulating factor and gamma interferon, but only MP and PPD were able to induce IL-2 mRNA. MP were unable to stimulate a consistent expression of the genes encoding for IL-4, IL-5, and IL-10, while low, sometimes barely detectable levels of these cytokine mRNAs were observed in PPD- or IL-2-stimulated PBMC cultures. When protein synthesis of MP-stimulated PBMC was inhibited by cycloheximide, a superinduction of mRNAs for IL-4 and IL-10 and, more markedly, gamma interferon was observed. Overall, these results highlight the powerful, selective induction of cytokine gene expression by MP constituents of C. albicans in human PBMC cultures, thus providing some functional clues to explain the efficient state of the anticandidal response in normal human subjects.

Neutralizing antibody to interleukin 4 induces systemic protection and T helper type 1-associated immunity in murine candidiasis

An interleukin 4 (IL-4)-specific monoclonal antibody (mAb) was administered to mice infected systemically with the yeast Candida albicans, and the animals were monitored for mortality, development of delayed-type hypersensitivity, production of antibodies of different isotypes, release of IL-2, IL-4, IL-6, and interferon gamma (IFN-gamma) in vitro by splenic CD4+ lymphocytes, and levels of IL-4 and IFN-gamma mRNA in these cells. Neutralization of IL-4 by three weekly injections of mAb in several independent experiments resulted in an overall cure rate of 81% versus 0% of controls. Cure was associated with efficient clearance of the yeast from infected organs and histologic evidence of disease resolution, detection of strong T helper type 1 (Th1) responses, and establishment of long-lasting protective immunity. Soon after infection, and as a result of the first or second injection of mAb, there was a decrease in IL-4 mRNA in CD4+ cells, which was accompanied by an increase in the levels of IFN-gamma-specific transcripts. Our data thus indicate that the production of IL-4 by Th2 cells may limit Th1-associated protective immunity in murine candidiasis.

Antigen-specific cytolysis of infected cells in murine candidiasis

Immune L3T4+ and Lyt-2+ lymphocytes play an important role in the acquired resistance of mice to challenge with virulent Candida albicans, and release macrophage-activating cytokines in response to yeast cells in vitro. To determine whether antigen (Ag)-specific cytotoxic T lymphocytes are generated during fungal infection, purified L3T4+ and Lyt-2+ lymphocytes from immunized mice were cultured in the presence of syngeneic accessory cells, Candida Ag, and IL-2. Yeast-infected bone marrow macrophages and peritoneal exudate neutrophils were used as target cells in a standard 51Cr release assay. Ag-specific, MHC-unrestricted lysis of infected macrophages was evident with immune Lyt-2+ cells after 5-10 days in culture. Under the same experimental conditions, the cytotoxic activity of L3T4+ cells was negligible, but its expression could be induced by the addition of anti-CD3 antibody. Culturing immune Lyt-2+ cells for shorter periods of time (1-2 days) resulted in preferential lysis of infected neutrophils. In addition, at limiting effector cell numbers, Ag-specific MHC-restricted lymphocytes with cytotoxic activity to infected macrophages could be identified. We suggest that C. albicans infection stimulates multiple cytotoxic T-cell precursors with varying recognition stringency, which may have an important role in antifungal resistance in vivo.

Th1 and Th2 cytokine secretion patterns in murine candidiasis: association of Th1 responses with acquired resistance

Two chemically mutagenized agerminative variants of Candida albicans were used to immunize mice against challenge with highly virulent cells of the parent strain. Although both mutants (Vir- 3 and Vir- 13) resulted in nonlethal infection and could be recovered from mouse organs for many days after the intravenous inoculation of 10(7) to 10(6) cells, significant protection to systemic challenge with virulent C. albicans was induced by only one (Vir- 3) of the two variants. Anticandidal resistance in Vir- 3-infected mice was associated with the occurrence in vivo of strong delayed-type hypersensitivity to Candida antigen, detection in vitro of highly fungicidal effector macrophages, and presence in the serum of a large proportion of Candida-reactive antibodies of the immunoglobulin G2a isotype. Bulk cultures of purified CD4+ lymphocytes from mice infected with either mutant were compared for their ability to produce gamma interferon (IFN-gamma), interleukin-2 (IL-2), IL-4, and IL-6 in vitro. After stimulation with specific antigen, CD4+ cells from Vir- 3-immunized mice released large amounts of the Th1-specific cytokines, IFN-gamma and IL-2, at a time when CD4+ cells from Vir- 13-infected mice predominantly secreted the characteristic Th2 cytokines, IL-4 and IL-6. These results were confirmed by quantitative analysis of cytokine-producing Th1 and Th2 cells. In addition, only mice infected with Vir- 3 displayed a high frequency of CD8+ cells with the potential for in vitro lysis of yeast-primed bone marrow macrophages. Purified CD4+ cells from Vir- 3-infected mice, but not a mixture of these cells with CD4+ lymphocytes from mice infected with Vir- 13, could adoptively transfer delayed-type hypersensitivity reactivity onto naive mice. Taken together, these data suggest that both Th1 and Th2 CD4+ lymphocytes may be activated during experimental C. albicans infection in mice.

Enhancement of MHC class II antigen expression by exposure to Candida albicans

In oral infections with the yeast Candida albicans, the expression of MHC class II antigens on keratinocytes has been reported to be enhanced. In the present experiments, exposure to C. albicans or its products in vitro was found to increase the expression of class II MHC antigens on thioglycollate-induced mouse macrophages, and on LK cells (an antigen-presenting cell line). The implications of this finding for the understanding of immunoregulation and susceptibility to C. albicans infection are discussed.

Susceptibility of beige mutant mice to candidiasis may be linked to a defect in granulocyte production by bone marrow stem cells

The beige mutation in mice has a pervasive effect on mechanisms of host resistance to infectious agents. Best characterized are defects in granulocyte chemotaxis and phagocytosis, which are associated with increased susceptibility to bacteria, and a deficiency in the levels of natural killer (NK) cells, which has been linked to decreased resistance to both murine cytomegalovirus and the yeast Cryptococcus neoformans. The objective of the present experiments was to explore the cellular basis of the enhanced susceptibility of beige mice to systemic infection with the yeast Candida albicans. In contrast to murine cytomegalovirus and C. neoformans, infection with C. albicans did not induce any detectable NK cell activity in the spleen of bg/bg or bg/+ mice. Unfractionated bone marrow (BM) displayed some candidacidal activity, mediated by both phagocytic and nonphagocytic cells; however, there was no difference between homozygous and heterozygous mice in the effector function of normal BM cells or mononuclear cells derived from either short- or long-term BM cultures. On the other hand, peritoneal granulocytes from bg/bg mice were significantly more effective than those from bg/+ mice in killing Candida blastoconidia in vitro. A similar comparison of granulocytes from short-term BM cultures showed that the activities of cells from bg/bg and bg/+ mice were equivalent, indicating that the granulocytes derived from the peritoneal cavity of bg/bg mice had probably been exposed to some form of nonspecific stimulation in vivo. Somewhat surprisingly, long-term BM cultures did not support the continual growth of bg/bg granulocytes, and it is possible that the beige mutation may be associated with a lesion in the differentiation pathway that leads to the production of granulocytes. Taken together, the data indicate that, in beige mice, granulocytes rather than NK cells are a major determinant of natural resistance to C. albicans infections.

Murine candidiasis: sex differences in the severity of tissue lesions are not associated with levels of serum C3 and C5

Mice deficient in the fifth component of complement are known to be extremely susceptible to lethal challenge with Candida albicans. However, male mice, that have significantly higher concentrations of serum C5 than females, were markedly more susceptible to infection. This difference was observed in both susceptible (CBA/H) and resistant (BALB/c) mice. Levels of serum C3 likewise showed no correlation with susceptibility.