Binding of Trichophyton rubrum mannan to human monocytes in vitro

Commander-in-chief: monocytes rally the troops for defense against aspergillosis

The detrimental impact of fungal infections to human health has steadily increased over the past decades. In October of 2022, the World Health Organization published the first ever fungal-pathogen priority list highlighting increased awareness of this problem, and the need for more research in this area. There were four distinct fungal pathogens identified as critical priority groups with Aspergillus fumigatus (Af) being the only mold. Af is a common environmental fungus responsible for over 90% of invasive aspergillosis cases worldwide. Pulmonary protection against Af is critically dependent on innate effector cells with essential roles played by neutrophils and monocytes. In this review, we will summarize our current understanding of how monocytes help orchestrate antifungal defense against Af.

Phagocytic activity and oxygen metabolism of peripheral blood granulocytes from rabbits experimentally infected with Trichophyton mentagrophytes

Introduction

Phagocytic activity and oxygen metabolism of peripheral blood granulocytes from rabbits with experimental trichophytosis were assessed by flow cytometry.

Material and Methods

Virulent species of T. mentagrophytes var. granulosum (Tm-K) isolated from rabbits with natural trichophytosis was used for experimental infection. The phagocytic activity of granulocytes was measured in whole blood by flow cytometry using the commercial Phagotest kit. Oxidative burst was measured in whole blood by flow cytometry using the commercial Bursttest kit.

Results

It was found that rabbits were susceptible to infection with Trichophyton mentagrophytes under experimental conditions. The analysis of the phagocytic activity indices and oxygen metabolism of granulocytes in peripheral blood of infected rabbits showed that changes of the indices were connected with the progression and regression of the disease. A significant decrease in phagocytic activity and oxygen metabolism was observed during development of fungal lesions and it remained similar throughout the progress of the disease. The highest means of the percentage of activated and ingesting phagocytes and a significant increase in the mean fluorescence intensity (representing the number of ingested bacteria) were observed during spontaneous recovery. Therefore, the decrease or increase in the indices of phagocytic activity and oxygen metabolism of granulocytes from rabbits experimentally infected with T. mentagrophytes is somehow related to the progress of infection and suppressive activity of the fungus, whose elimination during recovery caused significant increases in investigated indices of non-specific cellular immunity.

Conclusion

The results of the present investigation confirm that the mechanism of oxygen-dependent killing is crucial in infections caused by T. mentagrophytes.

Phagocytic Activity and Oxygen Metabolism of Peripheral Blood Granulocytes from Rabbits Experimentally Infected with Trichophyton Mentagrophytes

Introduction

Phagocytic activity and oxygen metabolism of peripheral blood granulocytes from rabbits with experimental trichophytosis were assessed by flow cytometry.

Material and Methods

Virulent species of T. mentagrophytes var. granulosum (Tm-K) isolated from rabbits with natural trichophytosis was used for experimental infection. The phagocytic activity of granulocytes was measured in whole blood by flow cytometry using the commercial Phagotest kit. Oxidative burst was measured in whole blood by flow cytometry using the commercial Bursttest kit.

Results

It was found that rabbits were susceptible to infection with Trichophyton mentagrophytes under experimental conditions. The analysis of the phagocytic activity indices and oxygen metabolism of granulocytes in peripheral blood of infected rabbits showed that changes of the indices were connected with the progression and regression of the disease. A significant decrease in phagocytic activity and oxygen metabolism was observed during development of fungal lesions and it remained similar throughout the progress of the disease. The highest means of the percentage of activated and ingesting phagocytes and a significant increase in the mean fluorescence intensity (representing the number of ingested bacteria) were observed during spontaneous recovery. Therefore, the decrease or increase in the indices of phagocytic activity and oxygen metabolism of granulocytes from rabbits experimentally infected with T. mentagrophytes is somehow related to the progress of infection and suppressive activity of the fungus, whose elimination during recovery caused significant increases in investigated indices of non-specific cellular immunity.

Conclusion

The results of the present investigation confirm that the mechanism of oxygen-dependent killing is crucial in infections caused by T. mentagrophytes.

The Role of Phagocytes and NETs in Dermatophytosis

Innate immunity is the host first line of defense against pathogens. However, only in recent years, we are beginning to better understand the ways it operates. A key player is this branch of the immune response that are the phagocytes, as macrophages, dendritic cells and neutrophils. These cells act as sentinels, employing specialized receptors in the sensing of invaders and host injury, and readily responding to them by production of inflammatory mediators. They afford protection not only by ingesting and destroying pathogens, but also by providing a suitable biochemical environment that shapes the adaptive response. In this review, we aim to present a broad perspective about the role of phagocytes in dermatophytosis, focusing on the mechanisms possibly involved in protective and non-protective responses. A full understanding of how phagocytes fit in the pathogenesis of these infections may open the venue for the development of new and more effective therapeutic approaches.

Characterization of the cellular immunity in patients presenting extensive dermatophytoses due to Trichophyton rubrum

Dermatophytes invade the stratum corneum of the skin and other keratinized tissues such as hair and nails, and Trichophyton rubrum causes approximately 80% of cutaneous mycoses in humans. To evaluate the cellular immune response of patients with extensive dermatophytosis caused by T. rubrum, we evaluated lymphocyte populations, the lymphoproliferative response to: phytohaemagglutinin (PHA); anti-CD3 (OKT3); and pokeweed mitogen (PWM), Candida sp. (CMA), an extract of T. rubrum, and the main fungal epitope TriR2 (T). We also evaluated interleukin (IL)-4, IL-10, IL-12 and IFN-γ after stimulation by PHA, CMA and TriR2. The immunophenotyping showed no differences between patients and controls. The lymphoproliferation test showed significant differences between the groups stimulated by PWM and CMA, as well as against TriR2, being significantly higher for the control group. Conversely, there were similar results for the groups after stimulation by the extract. The cytokines' quantification showed a significant difference between the groups only for IFN-γ stimulated by PHA and TriR2. We can conclude that the fungal extract can stimulate lymphoproliferation by both groups' lymphocytes. However, the response to Tri r2 was more specific. We showed that some patients with extensive dermatophytosis have normal cellular response, recognising both the extract and TriR2.

Pathogenesis of dermatophytosis

Despite the superficial localization of most dermatophytosis, host-fungus relationship in these infections is complex and still poorly elucidated. Though many efforts have been accomplished to characterize secreted dermatophytic proteases at the molecular level, only punctual insights have been afforded into other aspects of the pathogenesis of dermatophytosis, such as fungal adhesion, regulation of gene expression during the infection process, and immunomodulation by fungal factors. However, new genetic tools were recently developed, allowing a more rapid and high-throughput functional investigation of dermatophyte genes and the identification of new putative virulence factors. In addition, sophisticated in vitro infection models are now used and will open the way to a more comprehensive view of the interactions between these fungi and host epidermal cells, especially keratinocytes.

Onychomycosis in inflammatory bowel diseases

BACKGROUND

As far as we have sought for in Medline and PubMed, not one study until now has evaluated the prevalence of onychomycosis in patients with inflammatory bowel disease (IBD). As there are great evidence of immunological disturbances linked to IBD, a possible relationship of this nail infection in association with those diseases and the possible risk factors might be relevant in IBD patients.

METHODS

A case-control prospective study using combined direct smear and cultures for fungus was performed. Sociodemographics, clinical and laboratorial data were recorded at baseline and samples of suspected nails were collected from 141 IBD (61 men and 80 women) and from a group of 100 non-IBD subjects (41 men and 59 women). Direct smear and cultures were performed on each suspected case to exclude other onychodystrophies.

RESULTS

The incidence of onychomycosis in IBD patients was highly significant in comparison to non-IBD patients (14.9% vs. 6%, respectively, P < 0.05). The risk factors predisposing IBD patients to onychomycosis were older age (P = 0.02) and leucopoenia in those using azathioprine therapy (P = 0.04) beyond a trend to lymphopenia (P = 0.06). The dermatophytes predominated (76.2%) over yeasts (19%) and moulds (4.8%).

CONCLUSION

The prevalence of onychomycosis in IBD patients was expressively high (14.9%) in comparison with non-IBD patients. Considering the sociodemographic factors, any one but two were related to fungal onychomycosis incidence. Therefore, as far as we are concerned, IBD must be included in the high-risk underlying conditions for onychomycosis occurrence.

Glycosylphosphatidylinositols synthesized by Trichophyton rubrum in a cell-free system

The opportunistic fungi Trichophyton rubrum and T. mentagrophytes, are responsible for relatively non-inflammatory chronic dermatophytes infections in immunocompromised patients but also in healthy individuals. This chronic infection is associated with immunosuppressive effects of the cell wall components particularly the polysaccharides secreted by these organisms. We have studied glycosylphosphatidylinositol (GPI) anchor biosynthesis in the pathogenic fungus T. rubrum and could demonstrate that T. rubrum is able to synthesize GPI structures. Glycolipids synthesized in a cell-free system prepared from the dermatophyte T. rubrum and labeled with [3H]mannose, and [3H]galactose using GDP-[3H]mannose and UDP-[3H]galactose, respectively, were identified and structurally characterized as GPIs. The evolutionary conserved backbone of T. rubrum GPIs incorporates galactose. Further, all glycolipids lack the acyl group on the inositol which was shown for Saccharomyces cerevisiae and mammalian GPIs. Our data suggest significant differences in the GPI biosynthetic pathway between mammalian and T. rubrum cells that could perhaps be exploited for the development of an antimycotic for Trichophyton infection.

A highly efficient synthesis of an octasaccharide, the repeating unit of the cell-wall mannan of Trichophyton mentagrophytes and T. rubrum

A highly concise and effective synthesis of the mannose octasaccharide repeating unit of the cell-wall mannan of Trichophyton mentagrophytes and T. rubrum was achieved via 6-O-glycosylation of a tetrasaccharide acceptor with a tetrasaccharide donor, followed by deprotection. The key tetrasaccharide (11) was constructed by selective 6-O-glycosylation of allyl 3,4-di-O-benzoyl-alpha-D-mannopyranosyl-(1-->6)-2,3,4-tri-O-benzoyl-alpha-D-mannopyranoside with 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate, then with 2,3,4,6-tetra-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate. The tetrasaccharide acceptor (13) was obtained by selective 6-O-deacetylation of 11, while the tetrasaccharide donor 12 was obtained by deallylation of 11, followed by trichloroacetimidation.

Evaluation of lymphocytes subpopulations and natural killer cells in peripheral blood of patients treated for dermatophyte onychomycosis

Thirty-five patients with dermatophyte onychomycosis caused by Trichophyton rubrum, T. mentagrophytes var. granulosum, T. tonsurans and Epidermophyton floccosum were examined before treatment and 27 of these patients were examined again when they came to the control check up 3 months after completion of treatment. The immunological investigations, including evaluation of immunological competence, were performed in vivo through the determination of lymphoid cell immunophenotype by a flow cytometry technique. The quantitative composition of basic lymphocyte subpopulations and natural killer cells in the peripheral blood of 35 patients before the treatment was compared with a control group of 20 individuals. Statistically significant differences in the percentages of CD3+ T lymphocytes (P<0.05), T helper lymphocytes (CD4+) (P<0.05) and activated T lymphocytes (CD3+/HLA-DR+) (P<0.05) were obtained. In the control check-up examinations of 27 patients 3 months after completion of treatment, in comparison with the control group of 20 healthy individuals, highly statistically significant differences in percehtages of T lymphocytes (CD3+) (P<0.001) and T helper lymphocytes (CD4+) (P<0.01) were obtained. In five of these 27 patients the treatment resulted in failure. Comparing the group of 22 recovered patients with these five patients in whom the treatment result was failure, the only statistically significant difference obtained before as well as after the treatment was in B lymphocytes (CD19+) percentage (P<0.05). The results obtained confirm that impairments of the patients' cellular immunity are crucial factors influencing the course and results of treatment in dermatophyte onychomycosis.

NMR assignment of the galactomannan of Candida lipolytica

The chemical structure of the cell wall galactomannan of Candida lipolytica was analyzed using two-dimensional NMR techniques without chemical fragmentation. The H-1-H-2-correlated cross-peaks of the galactomannan indicated that it consists of an alpha-1,6-linked mannan backbone moiety with side chains. A sequential NMR assignment of the side chains through nuclear Overhauser effect (NOE) cross-peaks indicated that the triose side chain contains an alpha-1,2-linked galactopyranose unit at the non-reducing terminal. The structure was significantly different from the galactomannan of Trichophyton. The molar ratio of the side chains calculated from the H-1 signal dimensions indicated that ca. 45% of the backbone alpha-1,6-linked mannose units are not substituted with side chains and are responsible for the reactivity of the galactomannan with factor 9 serum.

NMR study of the galactomannans of Trichophyton mentagrophytes and Trichophyton rubrum

Around 90% of chronic dermatophyte infections are caused by the fungi Trichophyton mentagrophytes and Trichophyton rubrum. One of the causes of the chronic infection resides in the immunosuppressive effects of the cell-wall components of these organisms. Therefore we have attempted to identify the chemical structure of galactomannan, one of the major cell-wall components. The cell-wall polysaccharides secreted by T. mentagrophytes and T. rubrum were isolated from the culture medium and fractionated into three subfractions by DEAE-Sephadex chromatography. Analysis of each subfraction by NMR indicated that there are two kinds of polysaccharides present, i.e. mannan and galactomannan. The mannan has a linear backbone consisting of alpha1,6-linked mannose units, with alpha1,2-linked mannose units as side chains. The core mannan moiety of the galactomannan was analysed by a sequential NMR assignment method after removing the galactofuranose units by acid treatment. The result indicates that the mannan moiety has a linear repeating structure of alpha1,2-linked mannotetraose units connected by an alpha1,6 linkage. The H-1 signals of the two intermediary alpha1, 2-linked mannoses of the tetraose unit showed a significant upfield shift (Deltadelta=0.05-0.08 p.p.m.), due to the steric effect of an alpha1,6-linked mannose unit. The attachment point of the galactofuranose units was determined at C-3 of the core mannan by the assignment of the downfield-shifted 13C signals of the galactomannan compared with those of the acid-modified product. In these galactomannans there were no polygalactofuranosyl chains which have been found in Penicillium charlesii and Aspergillus fumigatus.

Cutaneous defenses against dermatophytes and yeasts

Predispositions to the superficial mycoses include warmth and moisture, natural or iatrogenic immunosuppression, and perhaps some degree of inherited susceptibility. Some of these infections elicit a greater inflammatory response than others, and the noninflammatory ones are generally more chronic. The immune system is involved in the defense against these infections, and cell-mediated immunity appears to be particularly important. The mechanisms involved in generating immunologic reactions in the skin are complex, with epidermal Langerhans cells, other dendritic cells, lymphocytes, microvascular endothelial cells, and the keratinocytes themselves all participating in one way or another. A variety of defects in the immunologic response to the superficial mycoses have been described. In some cases the defect may be preexistent, whereas in others the infection itself may interfere with protective cell-mediated immune responses against the organisms. A number of different mechanisms may underlie these immunologic defects and lead to the development of chronic superficial fungal infection in individual patients. Although the immunologic defects appear to be involved in the chronicity of certain types of cutaneous fungal infections, treatment of these defects remains experimental at the present time.

The dermatophytes

The etiologic agents of the dermatophytoses (ringworm) are classified in three anamorphic (asexual or imperfect) genera, Epidermophyton, Microsporum, and Trichophyton. Species capable of reproducing sexually belong in the teleomorphic genus, Arthroderma, of the Ascomycota. On the basis of primary habitat association, they may be grouped as geophilic (soil associated), zoophilic, and anthropophilic. Adaptation to growth on humans by most geophilic species resulted in diminished loss of sporulation, sexuality, and other soil-associated characteristics. The dermatophytes have the ability to invade keratinized tissue (skin, hair, and nails) but are usually restricted to the nonliving cornified layer of the epidermis because of their inability to penetrate viable tissue of an immunocompetent host. However, invasion does elicit a host response ranging from mild to severe. Acid proteinases, elastase, keratinases, and other proteinases reportedly act as virulence factors. The development of cell-mediated immunity correlated with delayed hypersensitivity and an inflammatory response is associated with clinical cure, whereas the lack of or a defective cell-mediated immunity predisposes the host to chronic or recurrent dermatophyte infection. Chronic dermatophytosis is mostly caused by Trichophyton rubrum, and there is some evidence that mannan produced by this fungus suppresses or diminishes the inflammatory response. Since dermatophytes cause a communicable disease, modes of transmission and control are discussed as well as a survey of recent trends in therapy. Collection of specimens, culture media, and tests for identification are also presented. Genetic studies have led to an understanding of incompatibility mechanisms, pleomorphism and variation, resistance to griseofulvin, and virulence. Molecular biology has contributed to our knowledge of the taxonomy and phylogenetic relationships of dermatophytes.

Dermatophytosis and the immune response

Dermatophytes are eliminated from the skin by a cell-mediated immune reaction. Immunity is acquired by active infection. The inflammatory reaction that ensues may increase the proliferatory activity of keratinocytes, causing the fungus to be sloughed from the skin surface. Nonspecific mechanisms of defense prevent invasion into the dermis and bloodstream even in the absence of immunity. Serum inhibitory factor robs fungi of iron, an essential nutrient. The cell walls of the organism activate complement through the alternative pathway and inhibit fungal growth. Polymorphonuclear leukocytes adhere to opsonized and unopsonized hyphae to inhibit growth of the dermatophyte and perhaps damage or kill it. The fungas secrets keratinases and other enzymes that allow the dermatophyte to burrow deeper into the stratum corneum. Mannan from the cell wall of Trichophyton rubrum and a lipophilic toxin associated with it might inhibit cell-mediated immunity and keratinocyte proliferation.

Immune response and host resistance of humans to dermatophyte infection

Clearing of dermatophyte infection depends on a cell-mediated immune response. Antibodies to fungi, although present in infected persons, are ineffective at ridding the skin of fungi. Experiments in which human volunteers were deliberately infected with dermatophytes identified two major groups on the basis of cellular immune responsiveness: (1) those who mount decisive delayed-type hypersensitivity that results in clearing of the infection, and (2) those who have absent or defective cellular immunity that prevents them from mounting an effective response to dermatophytes and thus predisposes them to chronic or recurrent dermatophyte infection. The courses of experimental infection in these two groups were compared with skin test results. The presence of an acute inflammatory infection was correlated with delayed-type (T-cell-mediated) hypersensitivity to a trichophytin skin test and the ability of persons affected in this manner to achieve mycologic cure. In contrast, chronic infection was associated with high immediate (anti-Trichophyton-IgE-mediated) hypersensitivity and low or waning delayed-type (T-cell-mediated) hypersensitivity to trichophytin. Despite this immune deficiency, these persons had a normal response to other infectious agents and skin test antigens. This type of selective and perhaps induced immune deficit may be relatively common, because persons chronically infected with a dermatophyte constitute 10% to 20% of the general population.

Suppression of immunity and inflammation by products produced by dermatophytes

When normal, previously uninfected hosts are exposed to dermatophytes under experimental occlusive conditions, infections develop and cell-mediated immunity is induced. Subsequent exposure to dermatophytes under the same conditions elicits an immune response that is capable of curing the infection, once occlusion is removed. Lymphocytes or monocytes involved in the immune response may produce cytokine growth factors that foster stratum corneum turnover and shedding of the fungus from the skin surface. Chronic dermatophyte infections develop when conditions of the local environment or virulence factors of the fungus outweigh the capabilities of cell-mediated immunity, or when a person does not develop cell-mediated immunity to fungal antigens. Even if immunity does develop, certain dermatophytes such as Trichophyton rubrum produce substances that diminish the immune response. One class of these substances, the mannans, can indirectly inhibit stratum corneum turnover. A nonresponsive host immune system or the suppression of the immune response by products produced by dermatophytes can prevent complete eradication of the fungus or predispose to reinfection.