Amphibian cellular immune response to chytridiomycosis at metamorphic climax
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Hicks, Allan
Lanctôt, Chantal
McCallum, Hamish
Newell, David
Grogan, Laura F
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Abstract
The fungal disease chytridiomycosis (caused by Batrachochytrium dendrobatidis [Bd]) is a primary contributor to amphibian declines. The frog metamorphic stages, characterised by extensive physiological reorganisation and energy expenditure, have heightened susceptibility to Bd. However, little is known about how these metamorphic stages respond immunologically to Bd infection. In this study, we examined Bd infection and the cellular immune response of Mixophyes fleayi at Gosner stages 40, 42 and 45, using blood smears and skin and liver histology. Although proportional differences were observed, the impact of Bd exposure appeared negligible prior to Gosner stage 45 (onset of morbidity), with no significant differences observed in absolute leukocyte counts for blood or liver samples between control and Bd-exposed groups at Gosner stages 40 and 42. Animals exhibiting clinical signs at Gosner stage 45 demonstrated significant elevation in liver leukocyte counts, blood neutrophil and monocyte counts and neutrophil-to-lymphocyte ratios. These findings are reminiscent of the amplified inflammatory response characteristic of immunopathology in clinically infected amphibians. Interestingly, a subset of exposed animals that had apparently cleared infections at Gosner stage 45 had similar blood leukocyte counts but reduced liver leukocyte counts compared to naïve controls. This could be a consequence of prior cellular consumption during pathogen removal or effective immune regulation via anti-inflammatory protective feedback mechanisms. We recommend targeted gene expression analyses (e.g. immunomodulatory cytokines) to establish the mechanisms responsible for the varied immune expression and infection outcomes across metamorphosis.
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Immunologic Research
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73
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© The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
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Immunology
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Humphries, JE; Hicks, A; Lanctôt, C; McCallum, H; Newell, D; Grogan, LF, Amphibian cellular immune response to chytridiomycosis at metamorphic climax, Immunologic Research, 2025, 73, pp. 44