The thymus dependency of acquired resistance to Trichophyton mentagrophytes dermatophytosis in rats

The interplay among Th17 and T regulatory cells in the immune dysregulation of chronic dermatophytic infection

The delineation of the pathogenic interaction between the host skin immune responses and dermatophytes has remained indigent. The obscure enigma in host-dermatophyte immunopathogenic interactions is the T regulatory (Treg) and T-helper (Th) 17  cell role in maintaining immune homeostasis. We attempted to understand the regulation and recognition of lineage-specific response in chronic dermatophytic skin infection patients. The percentages of Th17 (CD4⁺CD161⁺IL23R⁺) and Treg (CD4⁺CD25⁺FoxP3⁺) cell subpopulations in the peripheral circulation of thirty chronic dermatophytic skin infection patients and twenty healthy individuals was determined. The serum cytokine levels were estimated for disease correlation. The mean duration of the disease was 10.68 ± 8.72 months, with Trichophyton mentagrophytes complex as the major pathogen. Total serum IgE level of patients was significantly higher compared to healthy controls (305 ± 117 vs 98.53 ± 54.55 IU/ml; p < 0.01). Expression of Th17 and Treg cell markers on CD4⁺ T cells was significantly elevated in patients than controls (p < 0.05). Comparatively, serum interleukin (IL)-4 and interferon (IFN)-γ levels were increased, with low IL-10 levels in patients. Our data envisages a complex immune dysfunction in chronic dermatophytosis, arising either as a result of dermatophyte exposure or paradoxical precedence of disease establishment. Designing new treatment strategies and preventing recurrences are challenges for future research.

Are Th17 Cells Playing a Role in Immunity to Dermatophytosis?

Despite their superficial localization in the skin, pathogenic dermatophytes can induce a complex but still misunderstood immune response in their hosts. The cell-mediated immunity (CMI) is correlated with both clinical recovery and protection against reinfection, and CD4+ T lymphocytes have been recognized as a crucial component of the immune defense against dermatophytes. Before the discovery of the Th17 pathway, CMI was considered to be only dependent of Th1 cells, and thus most studies on the immunology of dermatophytosis have focused on the Th1 pathway. Nevertheless, the fine comparative analysis of available scientific data on immunology of dermatophytosis in one hand and on the Th17 pathway mechanisms involved in opportunistic mucosal fungal infections in the other hand reveals that some key elements of the Th17 pathway can be activated by dermatophytes. Stimulation of the Th17 pathway could occur through the activation of some C-type lectin-like receptors and inflammasome in antigen-presenting cells. The Th17 cells could go back to the affected skin and by the production of signature cytokines could induce the effector mechanisms like the recruitment of polymorphonuclear neutrophils and the synthesis of antimicrobial peptides. In conclusion, besides the Th1 pathway, which is important to the immune response against dermatophytes, there are also growing evidences for the involvement of the Th17 pathway.

Association between onychodystrophy and human T-lymphotropic virus type 1 infection

OBJECTIVE

To assess the association between human T-lymphotropic virus type 1 (HTLV-1) infection and onychodystrophy.

METHODS

This was a cross-sectional study. At our institute, we provide HTLV-1 testing to relatives of HTLV-1-infected people and patients with suspected HTLV-1-associated diseases. The diagnosis of onychodystrophy was made clinically before testing for HTLV-1; the number and distribution of affected nails was registered. We assessed the association between onychodystrophy and HTLV-1 through bi- and multivariable analyses. Logistic regression was used to adjust for age, sex, and indication for HTLV-1 testing, using six affected nails (90(th) percentile) as the cut-off point.

RESULTS

Between April 2006 and March 2008, we included 893 subjects; their mean age was 38 years (standard deviation 19 years), and 527 (59%) were women. Onychodystrophy of one or more nails was observed in 323 participants (36%), and 236 subjects (26%) were HTLV-1-positive. The median number of affected nails was higher in HTLV-1-positive than in HTLV-1-negative subjects (Mann-Whitney test, p < 0.001). Thirty-eight of 97 subjects with six or more affected nails (39%) were HTLV-1-infected, compared to 198 of 796 subjects with fewer than six affected nails (25%) (crude OR 1.9, 95% confidence interval (CI) 1.2-3.1; p = 0.003). This association remained significant in the multiple logistic regression model (adjusted OR 2.0, 95% CI 1.2-3.3; p = 0.005).

CONCLUSIONS

There is an independent association between HTLV-1 infection and onychodystrophy. Patients with an HTLV-1 infection might have a higher risk for onychomycosis given the abnormal nail plate and a decreased T-cell-mediated immunologic response.

Animal model of dermatophytosis

Dermatophytosis is superficial fungal infection caused by dermatophytes that invade the keratinized tissue of humans and animals. Lesions from dermatophytosis exhibit an inflammatory reaction induced to eliminate the invading fungi by using the host's normal immune function. Many scientists have attempted to establish an experimental animal model to elucidate the pathogenesis of human dermatophytosis and evaluate drug efficacy. However, current animal models have several issues. In the present paper, we surveyed reports about the methodology of the dermatophytosis animal model for tinea corporis, tinea pedis, and tinea unguium and discussed future prospects.

CD4+ and CD8+ T cells mediated direct cytotoxic effect against Trichophyton rubrum and Trichophyton mentagrophytes

BACKGROUND

The cellular immune system is the most dominant factor in curing acute dermatophytosis. However, the exact immune mechanisms involved in generating this defense are complex and still obscure. The aim of this study was to investigate the fungicidal mechanism of T cells in the normal population versus patients with chronic fungal infections.

METHODS

Thirty patients were included in the study: 15 patients with chronic dermatophytosis and 15 normal healthy patients with a history of acute dermatophytosis. The procedures were performed as follows. 1) Proliferation and cytotoxic activity of lymphocytes cultured with various dermatophytes homogenate such as, Trichophyton rubrum, Trichophyton mentagrophytes and Microsporum gypseum. 2) CD4(+) and CD8(+) T cells were separated by magnetic beads before culture with fresh spores of either T. mentagrophytes or T. rubrum. 3) Routine histology and ultrastructural study were performed to illustrate the mode of activity of the T cells against the dermatophytes.

RESULTS

The study showed that both CD4 and CD8 possess cytotoxic activity against dermatophytes. However, the results demonstrated a suppression of lymphocyte proliferation response and a significant lower cytotoxic effect in chronic patients. Ultra structure and histological evaluation of the culture of hyphae with CD4(+) or CD8(+) T cells showed more prominently destructive effects in the culture of cells that had been obtained from normal population than those of patients with long-lasting fungal infections.

CONCLUSION

The study suggests a selective impairment of lymphocyte function against dermatophytes, in patients with chronic dermatophytoses.

Effective treatment for dermatophytoses of the foot: effect on restoration of depressed cell-mediated immunity

Superficial infections caused by dermatophyte fungi are highly prevalent throughout the world. Modern antimycotic agents like the azole itraconazole or the synthetic allylamine terbinafine greatly improved treatment outcomes in comparison with former therapeutic options with griseofulvin or older azole preparations like ketoconazole or fluconazole. In randomized trials involving patients with dermotophytoses, a great effectiveness has been shown especially for terbinafine. Oral terbinafine in general is well tolerated, has a low potential for drug interactions and, therefore, may be the most often used therapeutic agent for dermatophyte onychomycosis. However, there is a group of patients suffering from chronic dermatophytoses or early reinfections after antifungal therapy. For these patients, a depression of the delayed-type hypersensitivity reactivity was postulated. Just recently, effective antimycotic treatment, in particular with terbinafine, was shown to enhance and restore cell-mediated immunity, which potentially improves the therapeutic outcome even for this group of patients.

Disease mimicry--a pathogenetic concept for T cell-mediated autoimmune disorders triggered by molecular mimicry?

Molecular mimicry is considered as a mechanism by which infectious pathogens may break immunological tolerance and cause autoimmune disease. It implicates that peptides shared between pathogen and host may induce cross-reactive immune reactions. According to this hypothesis, the resulting autoimmune response actually represents a secondary immune response. It is mediated by cross-reactive T cells that have been educated in a primary immune response against a particular pathogen. Using psoriasis vulgaris as a model, this article discusses the potential functional consequences molecular mimicry should have for the resulting autoimmune disease. It proposes that due to the functional memory of T cells, which is an integral feature of adaptive immunity, the phenotype of an autoimmune disease induced by molecular mimicry should reflect the immune mechanisms raised in the primary immune response. This process might be called 'disease mimicry'.

Psoriasis is mediated by a cutaneous defect triggered by activated immunocytes: induction of psoriasis by cells with natural killer receptors

This study was performed to ask whether psoriasis is a unique pathologic response of epidermis of psoriatic patients, or cells with natural killer receptors can induce psoriatic changes in skin from nonpsoriatic donors. Human nonlesional skin from five psoriatics, as well as from seven nonpsoriatics was grafted on to beige-SCID mice. Lymphocyte lines with natural killer activity, and mixed natural killer, natural killer T cell phenotype, were generated by culture of peripheral blood mononuclear cells from both psoriatic, and normal donors, in 100 U interleukin-2 per ml for 14 d. Natural killer cells were injected into the human skin grafts, and the grafts were harvested after 4 wk. Injection of natural killer cells from psoriatic donors into autologous nonlesional psoriatic skin resulted in classic psoriasis histology with a significant increase in epidermal thickness, and proliferation, as well as expression of epidermal human leukocyte antigen DR, intercellular adhesion molecule-1, CD1d, and K-16. Superantigen stimulation was not necessary. In contrast, injection of natural killer cells from normal donors into autologous normal skin did not induce the histology of psoriasis, but that of psoriasiform dermatitis. This is a nonspecific reaction pattern. These grafts also exhibited a significant increase in epidermal thickness, and proliferation. Differences from psoriasis included mild epidermal edema (spongiosis), hypergranulosis, irregular elongation of rete ridges, and lack of thinning of the suprapapillary plate. Injection of allogeneic natural killer cells into grafts also resulted in psoriasiform dermatitis, regardless of the source of natural killer cells, or skin. Psoriasis induction by cells with natural killer receptors appears to be dependent upon the source of skin. This suggests that psoriasis results from a cutaneous defect that is triggered by an autoimmune activation.

Un-cross-linked fibrin substrates inhibit keratinocyte spreading and replication: correction with fibronectin and factor XIII cross-linking

Wound repair is characterized by the presence of a fibrin-rich matrix, but the effect of fibrin on re-epithelialization remains unclear. In this study, we determined the effects of different fibrin matrices on cultured human neonatal keratinocytes. Using purified fibrinogen and fibrin gels generated by the enzymatic action of thrombin, batroxobin (it leads to retention of fibrinopeptide B), or Agkistrodon contortrix thrombin-like enzyme (ACTE; it leads to retention of fibrinopeptide A), we determined the effect of each of these matrices on keratinocyte morphology, attachment, spreading, and replication as compared to tissue culture plastic. Morphologically, keratinocytes seeded on fibrin surfaces were more rounded and formed three-dimensional structures. Specific cell attachment, as measured at either 37 degrees C or 4 degrees C, was not altered on the different fibrin substrates (P > .05) but was increased on fibrinogen and factor XIII cross-linked fibrin (P < .01). However, keratinocytes seeded on fibrin, regardless of the presence or absence of fibrinopeptides A or B, showed a marked decrease (up to 71%) in cell numbers by days 5 (P = .0357) and 10 (P = .0114). Keratinocyte spreading was decreased by 78.8% (P = .0006), 80.3% (P = .0001), and 89.2% (P = .0001) on thrombin-, batroxobin-, and ACTE-generated fibrin, respectively, but not on fibrinogen-coated dishes. However, either the addition of fibronectin or cross-linking of fibrin with factor XIII allowed full keratinocyte spreading to occur (P = .0002 and P = .0013, respectively). We conclude that fibrin inhibits keratinocyte spreading in the absence of other matrix or plasma proteins or cross-linking by factor XIII.

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.

SDS-PAGE separation of dermatophyte antigens, and western immunoblotting in feline dermatophytosis

Water-soluble antigens liberated from the disrupted mycelium of nine dermatophytes (seven isolates of Microsporum canis, one each of Microsporum gypseum and Trichophyton mentagrophytes) were compared by analytical slab SDS-PAGE. No substantial differences were observed between the protein bands of the M. Canis isolates, but certain distinctive bands were apparent in the other two species examined. Western immunoblotting using M. canis-derived antigens separated by SDS-PAGE was used to investigate the humoral immune response in 79 cats with naturally-occurring dermatophytosis (72 with M. canis, six with M. gypseum and one with T. mentagrophytes) and this information was compared to results of immunoblots from 46 control (non-dermatophyte exposed) cats. Seven dominant bands (bands which occurred frequently and stained heavily) were identified in immunoblots from the dermatophyte-infected cats with apparent molecular weights varying between 39 and 120 kD. None of these bands were totally specific markers for dermatophytosis as a variable proportion of the control cats showed reactivity to all these proteins. However, most (73%) of the dermatophyte-infected cats showed reactivity to six or seven of the identified bands whereas most (80%) of the control cats showed reactivity to between zero and three of these bands (p < 0.005). Western immunoblotting could be used to select individual immunodominant antigens for further evaluation of protective (cell-mediated) immunity.

Human dermatophyte-responsive T-cell lines recognize cross-reactive antigens associated with mannose-rich glycoproteins

Resistance to dermatophyte infections has been shown to be mediated in part by T lymphocytes. The dermatophyte antigens recognized by human T lymphocytes and their degree of cross-reactivity were analyzed. Dermatophyte-responsive T-cell lines were generated by in vitro sensitization to crude fungal extracts obtained from Trichophyton rubrum, Trichophyton tonsurans, Microsporum canis and Epidermophyton floccosum. Proliferation was measured by incorporation of 3H-thymidine. The human T-cell lines responded to fungal extracts derived from these various dermatophyte species, demonstrating the recognition of cross-reactive antigens by human T cells. However, the T cells were dermatophyte-specific as they did not respond to herpes antigen, nor did herpes-specific T cells derived from the same donors respond to dermatophyte antigens. The mannose-rich glycoprotein fraction (mannan) isolated from T. rubrum was able to induce proliferation of T-cell lines generated by stimulation with various fungal extracts. Furthermore, a T-cell line generated by stimulation with mannan derived from T. rubrum proliferated in response to extracts from various fungal species, indicating that a major cross-reactive dermatophyte T-cell antigen was present in the mannose-rich glycoprotein fraction.

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.

Defective phagocytosis in chronic trichophytosis

Chronic trichophytosis as a primary clinical entity (primary chronic trichophytosis, PCT) is increasingly encountered in the literature. Its prevalent cause in Croatia is the anthropophilic form of Trichophyton interdigitale. Chronicity of the disease may result from immunological defects of the patients. Thus, in 62 patients with PCT: skin testing, enumeration of T- and B-lymphocytes in the peripheral blood, quantitation of immunoglobulin classes, and phagocytosis (random mobility, ingestion, digestion and extracellular killing) by peripheral blood leukocytes was tested. The findings were compared to those in healthy persons. Defective phagocytosis (random mobility, ingestion and digestion) was found in patients with PCT (P < 0.001). All the other results were within the control range. Therefore, PCT seems to be associated with defective phagocytosis of peripheral blood leukocytes in affected persons.

Immunoregulation of dermatophytosis

Dermatophytoses are superficial infections caused by a group of fungi, the dermatophytes, which invade keratinized tissue of skin, hair, and nails in humans and animals. The importance of normal immune function in resistance to dermatophytoses is substantiated by an increased susceptibility to chronic infection seen in patients with impaired immunological responses. Humoral and cell-mediated immunities are both elicited during the infection. However, specific antibodies to dermatophytes do not seem to play a major role in protective immunity. On the other hand, the development of cell-mediated immunity during the infection is critical in eliciting resistance to the disease. For instance, resolution of the disease in both naturally and experimentally infected humans and animals correlates with the development of delayed-type hypersensitivity (DTH), whereas persistence of infection is frequently accompanied by poor in vitro blastogenic response and absent DTH. Furthermore, in experimentally infected mice, immunity to dermatophyte infection can be achieved by adoptive transfer of lymphoid cells, but not by serum, of infected donors. The present review includes an overview of published work and current research on the cellular events implicated in immunity to dermatophytosis. The role of humoral factors in such immunoregulation is also discussed.

Acquired immunity to Trichophyton mentagrophytes in thymus-grafted or peritoneal exudate cell-injected nude rats

Congenitally athymic "nude" (RNU/RNU) rats were grafted with syngeneic neonatal thymus glands and 30 days later cutaneously inoculated with Trichophyton mentagrophytes. Nude rats and thymus-grafted nude rats were susceptible to infection with T. mentagrophytes but only thymus-grafted nude rats cleared the dermatophytosis. Clearance of the fungal infection took twice as long (approximately 60 days) in thymus-grafted nude rats when compared with heterozygous euthymic (+/RNU) controls (approximately 35 days). Following clearance of the primary dermatophytosis, peritoneal exudate cells (PEC) were adoptively transferred from either thymus-grafted or heterozygous rats to nude rats. Eight of 12 PEC-recipient nude rats acquired the capacity to resolve T. mentagrophytes-induced dermatophytosis (mean clearance time was approximately 40 days). All heterozygous (+/RNU) rats, thymus-grafted nude rats (4/4), and 8 of 12 PEC-recipient nude rats, which had cleared a primary dermatophytosis also expressed delayed-type hypersensitivity and elevated serum antibody titers to trichophytin antigen. These results demonstrate that immunity to T. mentagrophytes can be acquired in congenitally athymic nude rats following thymus grafting or injection of PEC from syngeneic +/RNU rats; however, injection of PEC from trichophytin-sensitized +/RNU donor rats to nude recipient rats did not result in transfer of specific adoptive immunity to T. mentagrophytes. Interestingly, PEC transfer from non-sensitized +/RNU rats was comparable to thymus grafting in effecting clearance of T. mentagrophytes dermatophytosis. These results suggest that acquired immunity to T. mentagrophytes in the rat is T cell-dependent, and that the absence of functional T lymphocytes and not an epithelial defect results in chronic dermatophytosis in the nude rat.

The inhibitory effect of PUVA on the immunity of experimental dermatophytosis in guinea pigs

The effect of topical PUVA on the disease course and immunity of T. mentagrophytes dermatophytosis was investigated in guinea pigs. Animals which had been inoculated on nontreated skin showed mild erythematous lesions with scaling in a few days and then developed the most intense reaction between days 10 and 14. The lesions resolved completely by the third week. On the other hand, animals which had been inoculated on the PUVA-treated sites showed only mild squamous, erythematous lesions until the fourth postinfective week, when the intense reaction began to appear. Complete regression was observed by the fifth week in these animals. Trichophytin tests performed on the 14th day were positive in the guinea pigs of non-treated group, while negative in the PUVA-treated animals. The latter group revealed a positive reaction on the fifth week. PUVA did not show inhibitory effect on the sensitization by intracutaneous injection of trichophytin antigen. The PUVA treatment depleted the ATPase-positive Langerhans' cells. These results indicate that PUVA treatment suppresses the immunity of dermatophytosis and delays the spontaneous resolution of the lesions, and suggest that the Langerhans' cell is involved in the development of cell-mediated immunity in experimental dermatophytosis.

Antifungal therapy of dermatophytosis in guinea pigs and congenitally athymic rats

Guinea pigs and athymic nude (RNU/RNU) rats were used to assess the efficacy of three orally administered antifungal agents--Tolciclate, Tolnaftate, and Ketoconazole--against Trichophyton mentagrophytes dermatophytosis. All three antifungal agents inhibited the test strain of T. mentagrophytes in vitro. Antifungal agents were tested in intervention (oral therapy started 5 days after challenge) or prophylaxis (oral therapy started 5 days before challenge) protocols. Oral treatment of dermatophytosis on guinea pig skin demonstrated that Tolciclate and Tolnaftate alleviated clinical symptoms and shortened the duration of the dermatophytosis, in comparison to nontreated controls. Assessment of antifungal efficacy in the guinea pig model was time consuming (30-35 days) and variability in the duration and severity of clinical symptoms on guinea pig skin was common. Oral therapy of chronically infected athymic rats demonstrated that Tolciclate, Tolnaftate, and ketoconazole were effective antifungal agents in vivo. Obvious improvement in clinical symptoms of dermatophytosis (i.e. less erythema and fewer lesions) was evident with all three antifungal agents within 10 days of starting oral therapy. By day 20, athymic rats that were treated with either Tolciclate or Ketoconazole showed marked clinical improvement of the chronic dermatophytosis. Chronically infected athymic rats, which lack thymus matured T-cells, are a promising new model to evaluate the efficacy of antifungal agents by culture, histology, and visual observations of clinical symptoms.