ヒストプラスマ症は世界的に分布し,我が国では輸入真菌症として取り扱われてきた.現在までに人獣合わせて数十例が報告されているが,いくつかのヒト症例とイヌ4例およびウマ1例は渡航歴や輸入歴が無いので,国内感染であると推測されている.ヒストプラスマ症はその原因菌のvarietyによりカプスラーツム,ズボアジ,ファルシミノーズム型に分類され,中でもファルシミノーズム型はウマ,ロバ等の頚部や脚のリンパ管やリンパ節を特異的に侵し,四足獣から分離されたという事実によってのみ他の2種と区別されてきた.我が国でも,戦前,軍馬を中心に2万頭以上に「仮性皮疽」として確認され,日本も本症の流行地の1つとして認識されていた.一方,本邦のイヌ症例は一様に潰瘍と肉芽腫性病巣を伴った皮膚病巣を呈し,仮性皮疽と類似した症状で,呼吸器や消化器病変を欠いていた.4例中3例はパラフィン包埋された病理組織より検出したH.capsulatumのリボゾームRNA遺伝子のITS領域の解析からヒストプラスマ症と診断されている.このような皮膚症状だけを示したヒストプラスマ症は渡航歴の無いヒト症例で確認されており,さらにこの症例で分離された菌株の遺伝子を解析したところH. capsulatum var. farciminosumと同定されている.すなわち,仮性皮疽はウマなどに限らず,本邦ではヒトにも感染する人獣共通真菌症である.よってヒト症例からの検証,臨床症状および歴史的背景から,現時点では,本邦で発症したイヌのヒストプラスマ症もファルシミノーズム型と考えられる.
A delayed-type hypersensitivity (DTH) response to a dermatophyte antigen is one of the host defense mechanisms. Peripheral blood mononuclear cells from patients with dermatophytosis produce a high level of IFN-γ in response to stimulation with trichophytin. The presence of IFN-γ mRNA in skin lesions of dermatophytosis was detected using reverse transcription-polymerase chain reaction. IFN-γ-positive cells were observed immunohistochemically in the upper dermis of the skin lesions. These findings support the hypothesis that the skin lesions of dermatophytosis are associated with a Th1 response. The Th1 response, which is characterized by IFN-γ release, is thought to be involved in the host defense against dermatophytes and to reflect cutaneous reaction in dermatophytosis. The stimulation of trichophytin significantly enhanced the release of IL-8 from keratinocytes. These findings account for the accumulation of neutrophils beneath the stratum corneum. The capacity of trichophytin-stimulated keratinocytes to release an enhanced level of IL-8 thus suggests that these cells can indeed help to induce the acute inflammatory response seen in dermatophyte infection. It therefore appears that keratinocytes not only play an important structural role in the formation of a physical barrier to dermatophytes but may also play an important functional role in initiating cutaneous inflammatory reactions, which might be involved in the host defense againt dermatophytes. The production of IFN-γ by peripheral blood mononuclear cells from patients with tinea unguium in response to stimulation with trichophytin was not impaired in contrast to that from patients without tinea unguium. Comparable lymphocyte proliferation with trichophytin was observed in both groups. No deficiency in Th1 response to dermatophyte antigen was shown in patients with tinea unguium by measuring the release of IFN-γ, which plays a role in the effector phase of the DTH reaction. A deficiency of Th1 response to dermatophyte antigen, therefore, does not appear to play an important role in the establishment of tinea unguium.
Cryptococcus neoformans is a pathogenic basidiomycete with a defined sexual cycle involving mating between haploid yeast cells with a transient diploid state. We examined F1 progeny from a crossing between the urease-negative strain (environmental isolate, serotype A, mating type α, haploid) and a tester strain (B 3502 from NIH of USA; urease-positive, serotype D, mating type a, haploid) for serotype, mating type, ploidy and urease activity, and performed partial sequencing of the urease gene. Phenotypes of the F1 progeny and results of SSCP analyses suggested that the serotype AD strain of the F1 progeny is a hybrid of the parental serotype A and D strains.
A strain of Histoplasma capsulatum var. duboisii (deposited as IFM 50954 in Chiba University) was isolated from the cerebrospinal fluid of a female Ugandan patient infected with HIV. The isolate had in vitro urease activity on Christensen's urea agar slants, although the common belief is that H. capsulatum var. duboisii is urease negative, and is, considered one of the characteristic markers that distinguishes the three varieties of H. capsulatum. Forty H. capsulatum var. capsulatum, five H. capsulatum var. duboisii, and five H. capsulatum var. farciminosum isolates were evaluated for urease activity on Christensen's urea agar slants and for other qualitative and quantitative urease assays of activity. All 50 isolates of H. capsulatum used in this study were positive for urease activity, suggesting that urease activity may be universal characteristic of H. capsulatum. We also compared the urease activity and pathogenicity of seven H. capsulatum isolates that convert into yeast-form cells. Although isolate IFM 50954 showed moderate virulence in mice and moderate urease activity among tested H. capsulatum isolates, there was no correlation between level of urease activity and pathogenicity. In addition, scanning electron microscopy revealed that some microconidia of isolate IFM 50954 formed “double-cell” configurations that were attached to each other by narrow bases.