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The prevalence of Trichophyton-induced superficial skin mycosis is very high among human patients. Dermatophytes generally infect the epidermis, especially the stratum corneum, forming scales, hyperkeratosis, and vesicles. The important roles played by the immune system in Trichophyton infection are detection of fungal invasion and elimination of fungi.These immune mechanisms are presumed to involve not only innate immunity but also acquired immunity. Therefore, there is a substantial need for studies on treatment methods based on new basic knowledge, and the elucidation of immunological mechanisms of Trichophyton-induced inflammatory reactions is especially important.However, since Trichophyton cannot colonize on the mouse skin, we tried to develop a model for Trichophyton inflammation induced by trichophytin extracted from Trichophyton mentagrophytes using a method based on contact hypersensitivity.Trichophytin is a crude extract that mainly contains fungal cell wall constituents including β-glucan and zymosan. In this model, TLR2, TLR4, and dectin-1 were highly expressed, and production of IL-17A and IL23 was observed. This indicates that we succeeded in inducing fungal-specific inflammation in the mice.In this review, we introduce a mouse Trichophyton inflammation model developed to investigate the immunological mechanisms of Trichophyton-induced inflammatory reactions. In addition, we report results of evaluation of anti-inflammatory and anti-itching effects of anti-fungal agents using the inflammation model.

Interferon-gamma (IFN-gamma), interleukin 2 (IL-2) and granulocyte/macrophage colony-stimulating factor (GM-CSF) were detected in the culture supernatant after 72 hours incubation with trichophytin in the peripheral blood mononuclear cells (PBMC) obtained from a patient who had a dermatophyte infection. These findings indicate that this patient has peripheral T-lymphocytes that produced IFN-gamma, IL-2 and GM-CSF, which may play roles in the development of delayed-type hypersensitivity (DTH) reaction in the skin.

The authors investigated the specific immunological competence of 31 patients with dermatophytosis using tricophytin antigen. Among them, 54.8% showed reaction to the delay phase (48 h) in the following proportions: tinea inguinale, 75%; tinea pedis, 61.5%; tinea unguium, 50% and tinea corporis, 20%. Other 62.5% showed positive result to the early phase (30 m). The association between these reactions revealed that, although the majority of cases with early positive reaction showed negativity to the delayed reaction, 20.8% presented positively to both phases of the reaction. Out of the non-reactive patients to the delayed phase, 8 were submitted to the other cutaneous tests such as PPD, streptokinase, candidin, vaccinia and DNCB and showed preserved cellular immunity in 75%. These results suggest that, while using this reaction for immunological evaluation of patients with dermatophytosis, one should consider the overall immune status of the patient, the presence of early hypersensibility and the localization of the infection.

Cell-mediated immune responses were measured in 91 patients with dermatophytosis by means of delayed-type skin hypersensitivity to a purified trichophytin preparation (ethylene glycol method) and to tuberculin (purified protein derivative, PPD). The findings indicate that dermatophytes differ in their sensitizing capacity as measured by trichophytin skin sensitivity. Trichophyton mentagrophytes appeared to be a potent sensitizer compared with Trichophyton rubrum (p < 0.01), whereas Epidermophyton floccosum appeared as a moderate sensitizer. The localization of infection also affected the cell-mediated response to trichophytin, i.e. the frequency of reactions was 44% in tinea cruris and 33% in tinea pedis, while tinea pedis with nail infections elicited delayed-type reactivity in 60% of cases. On the basis of the significant difference (p < 0.001) in cell-mediated reactivity between chronically and non-chronically infected subjects as measured with trichophytin, it is concluded that the cell-mediated response is of importance for the development of host resistance to dermatophytic infections. This study provides further evidenced in support of the view that a partial defect in the cell-mediated system may be responsible for establishment of chronic dermatophytosis.

During primary Trichophyton mentagrophytes infection of strain 2 guinea pigs, the colony-forming units (CFU) of fungi present within the lesion peaked between days 7 and 14, whereas the severity of the lesion itself peaked between days 11 and 16. Concomitant with the latter peak, a pronounced depression in the in vitro mitogenic activity of spleen cells (SPC) and lymph node cells (LNC) was observed. Only after resolution of the primary infection (day 21) did LNC show increased deoxyribonucleic acid (DNA) synthesis in the presence of fungal antigens. During cutaneous reinfection, there was no distinct peak fungal load and CFU appeared to decrease steadily during the accelerated course of a reinfection disease. LNC from guinea pigs with severe, ulcerated reinfection lesions generally exhibited a heightened response to fungal antigen in vitro. LNC from guinea pigs with mild reinfection dermatophytosis had depressed in vitro reactivity to mitogens and dermatophyte antigen. The suppression of blastogenic activity during dermatophyte infection appeared to be associated with autologous serum components, since increased DNA synthesis resulted when SPC or LNC were cultured with fetal calf serum. The depressed in vitro DNA synthesis of lymphocytes (cultured with dermatophyte antigens) that were harvested during reinfection was not accompanied by an impaired ability of infected guinea pigs to respond with a delayed-type hypersensitivity skin test in vivo. These results support the hypothesis that experimental T. mentagrophytes dermatophytosis is a cell-mediated hypersensitivity disease that can be modified by immunosuppressive control mechanisms elaborated or induced by the fungus.

Guinea pigs infected with Trichophyton mentagrophytes developed a cutaneous fungal lesion and became skin test positive to fungal antigen (trichophytin). The cutaneous fungal lesion, while thought to be a cell-mediated response, differed histologically from the skin test site. Basophils were not demonstrated in biopsies of cutaneous fungal lesions, whereas basophils were numerous in biopsies of trichophytin skin test sites. When sensitization to trichophytin was accomplished by injection of hypha in complete Freund's adjuvant instead of infecting with live fungus, basophils could not be demonstrated in skin test sites. This report demonstrated that guinea pigs could be primed for cutaneous basophilic hypersensitivity (CBH) responses by infection with live fungus.

Trichophytin contact sensitivity was investigated in patients with dermatophytosis by patch testing with highly concentrated purified trichophytin on partially stripped skin. The lack of primary irritant reactions was confirmed on the skin of children. Positive patch tests were noted in 113 of 178 patients (63.5%). However, there was a great difference in the incidence of trichophytin contact sensitivity between cases with different clinical types. The highest frequency of positive patch tests was obtained in patients with the vesiculobullous type of tinea pedis (83.3%). In contrast, a very low incidence was noted in patients with tinea corporis (37%) and the squamous hyperkeratotic type of tinea pedis (36%). Causative organisms and the age and sex of the patients did not show a relationship with the reactivity. A diminished incidence of positive reactions was noted in atopic individuals and in patients seen in winter. Patients who had persistent or recurrent infections for a long period of time, especially those having inflammatory lesions, had a higher frequency of positive patch tests.

Five patients with atopy who had chronic dermatophytosis manifested an immediate and strong trichophytin skin reaction but no delayed reaction. This phenomenon may be caused by the neutralization of injected antigen by serum antibodies during the immediate reaction. When we injected a second dose of trichophytin into the wheal of the immediate reaction, 20 minutes after the first injection, a strong delayed reaction was elicited, demonstrating cell-mediated immune responses in these patients.

The examinations have been performed with glycoproteidic fractions of Trichophyton verrucosum (Tv-GP) and T. mentagrophytes (Tm-GP) purified by a method of gel chromatography. Trichophytins were intradermally injected at a dose of 2.0 ml (1.0 mg of protein) and the results were estimated after 24 and 72 h on the basis of differences in skin fold thickness (RGFS). In animals infected with lice or scabies in a farm free of trichophytosis the median value of RGFS was below 1.0 mm and maximal value was 2.0 mm. In a farm where trichophytosis caused by T. verrucosum was diagnosed positive reactions (RGFS above 4.0 mm) against the two trichophytins appeared in 90% of sick animals, 95% of convalescents and in 20% of animals without skin lesions but kept together with sick animals. In a part of diseased animals and exposed to infection apart from local reactions also appeared so called focal reactions characterized by appearance of fungal lesions followed by opening and crushing the crusts. There is a lack of relationship between intensity of allergic skin reaction and rate of fungal lesions. The animals infected with T. verrucosum cross-reacted with trichophytins Tv-GP and Tm-GP, allergic state persisted in convalescent animals after idiopatic disappearance of clinical symptoms. The performed studies point to a possibility of the use of allergic skin tests with a standardized trichophytins to evaluate immunological state in cattle with trichophytosis.

Patients with pure atopic dermatitis with and without tinea infection were investigated and compared with patients with long-lasting tinea infections and with controls, for presence of intracutaneous reactivity to trichoptin, Penicillium, Cladosporium and Alternaria antigens. RAST to Penicillium and Cladosporium was also performed. The results showed a lack of delayed reactivity, but an immediate reactivity to trichophytin in 50%/40% of atopic patients with/without tinea infection. Non-atopics infected with tinea showed 66% immediate and 33% delayed response to trichophytin. The reactivities in atopic dermatitis (but not in the non-atopic group) went general parallel with mould reactions tested intracutaneously or by RAST. It is assumed that a positive trichophytin reaction in atopic dermatitis does not necessarily mean sensitisation to dermatophytes, but is primarily the sign of a cross sensitivity to moulds.