The role of conventional TCRαβ+CD4+ or TCRαβ+CD8α+ single-positive (sp) T lymphocytes in adaptive immunity is well-recognized. However, non-conventional T cells expressing TCRαβ or TCRγδ but lacking CD4 and CD8α expression [i.e., CD4−CD8α− double-negative (dn) T cells] are thought to play a role at the interface between the innate and adaptive immune system. Dn T cells are frequent in swine, cattle or sheep and predominantly express TCRγδ. In contrast, TCRγδ+ T cells are rare in dogs. In this study, we identified a high proportion of canine dn T cells in the TCRαβ+ T cell population of PBMC, lymphatic and non-lymphatic organs. In PBMC, the frequency of this T cell subpopulation made up one third of the frequency of TCRαβ+CD4+ sp, and almost half of the frequency of TCRαβ+CD8α+ sp T cells (i.e., ~15% of all TCRαβ+ T cells). Among TCRαβ+CD4−CD8α− dn T cells of PBMC and tissues, FoxP3+ cells were identified indicating regulatory potential of this T cell subset. 80% of peripheral blood FoxP3+TCRαβ+CD4−CD8α− dn T cells co-expressed CD25, and, interestingly, also the FoxP3-negative TCRαβ+CD4−CD8α− dn T cells comprised ~34% CD25+ cells. Some of the FoxP3-positive TCRαβ+CD4−CD8α− dn T cells co-expressed GATA-3 suggesting stable function of regulatory T cells. The frequency of GATA-3 expression by FoxP3−TCRαβ+CD4−CD8α− dn T cells was even higher as compared with TCRαβ+CD4+ sp T cells (20.6% vs. 11.9%). Albeit lacking FoxP3 and CD25 expression, TCRγδ+CD4−CD8α− dn T cells also expressed substantial proportions of GATA-3. In addition, TCRαβ+CD4−CD8α− dn T cells produced IFN-γ and IL-17A upon stimulation. T-bet and granzyme B were only weakly expressed by both dn T cell subsets. In conclusion, this study identifies two dn T cell subsets in the dog: (i) a large (~7.5% in Peyer's patches, ~15% in lung) population of TCRαβ+CD4−CD8α− dn T cells with subpopulations thereof showing an activated phenotype, high expression of FoxP3 or GATA-3 as well as production of IFN-γ or IL-17A and (ii) a small TCRγδ+CD4−CD8α− dn T cell subset also expressing GATA-3 without production of IFN-γ or IL-17A. It will be exciting to unravel the function of each subset during immune homeostasis and diseases of dogs.

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Background: The yeast Malassezia pachydermatis is a commensal but also the most isolated pathogenic yeast in canine otitis externa. Essential oils (EOs) exhibit antimicrobial activity and thus could be an alternative for treatment of otitis. Objective: The aim of this study was to analyse the in vitro efficacy of EOs against M. pachydermatis isolates from canine ears. Materials and Methods: Twenty-two EOs were tested for their in vitro activity against 15 M. pachydermatis isolates by agar disc diffusion. In addition, diluted EOs were tested and volatile antifungal activity was analysed by vapour assay. Results: Most EOs showed in vitro efficacy against M. pachydermatis. A different susceptibility pattern of tested isolates was found. Overall, the most potential EO was lemon grass. Also, cinnamon leaf, clove, manuka, Indian melissa, oregano, palmarosa, and winter savory oil exhibited a strong antifungal activity. Volatile activity was proven by the inhibiting effect in vapour assay. Conclusion: EOs show in vitro activity against M. pachydermatis. This study gives scientific background for the use of EOs in veterinary medicine. Diverse susceptibility patterns of different M. pachydermatis strains emphasise the helpfulness of an aromatogram as one lead for the best choice of an EO for therapy. Antimykotische In-vitro-Wirksamkeit ätherischerÖle gegen Malassezia pachydermatis isoliert aus Hundeohren: Ein Bericht aus dem Routinelabor Schlüsselwörter Ätherische Öle · Malassezia pachydermatis · Otitis externa · Veterinärmedizin Zusammenfassung Einleitung: Der Hefepilz Malassezia pachydermatis gilt als Kommensale, ist aber gleichzeitig auch der am häufigsten isolierte Hefepilz bei caniner Otitis externa. Ätherische Öle könnten aufgrund ihrer antimikrobiellen Eigenschaften als alternative Therapie der Otitis verwendet werden. Zielsetzung: Ziel dieser Studie war die Untersuchung der antifungalen In-vitro-Wirksamkeit ätherischer Öle gegen M. pachydermatis-Isolate aus Hundeohren. Material und Methoden: Die In-vitro-Aktivität von 22 ätherischen Ölen wurde mittels Agar-Plättchen-Diffusionstest gegen 15 M. pachydermatis-Isolate untersucht. Zusätzlich wurden Verdünnungen der ätherischen Öle getestet und die volatile Wirkung mittels "vapour assay" analysiert. Ergebnisse: Die meisten ätherischen Öle zeigten in vitro eine Wirksamkeit gegen M. pachydermatis. Es konnte eine unterschiedliche Empfindlichkeit einzelner M. pachydermatis-Isolate gefunden werden. Lemongrasöl erwies sich als das po-tenteste ätherische Öl. Ebenfalls zeigten Zimtblätter-, Nelken-, Manuka-, indisches Melissen-, Oregano-, Palmarosa-und Bergbohnenkrautöl eine starke antifungale Wirksamkeit. Die volatile Wirkung konnte mittels "vapour assay" gezeigt werden. Schlussfolgerung: In vitro zeigen ätherische Öle eine Wirksamkeit gegen den Hefepilz M. pachydermatis. Diese Studie bietet eine wissenschaftliche Basis zur Anwendung ätherischer Öle in der Veterinärmedizin. Die unterschiedliche Empfindlichkeit der verschiedenen M. pachydermatis-Isolate gegenüber einzelner äther...

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