ZFIN is incorporating published figure images and captions as part of an ongoing project. Figures from some publications have not yet been curated, or are not available for display because of copyright restrictions.

ZFIN is incorporating published figure images and captions as part of an ongoing project. Figures from some publications have not yet been curated, or are not available for display because of copyright restrictions.

Phagocytes control Mucor circinelloides spores in innate granulomas in vivo. (A and B) We tested the mathematical prediction that proinflammatory cytokine expression supports phagocyte recruitment by evaluating the early transcription response (1 hpi) of two proinflammatory cytokine genes (tnf-α and il-8, coding for tumor necrosis factor alpha and interleukin-8, respectively) after spore exposure in control- and dexamethasone-treated fish. Dexamethasone-treated fish showed significantly lower levels of transcript for both cytokines (P < 0.01 [n = 6 with 15 fish each], Mann-Whitney U test). (C) While phagocyte-induced spore death was identified by our in silico modeling as an efficient mechanism to protect from onset of mucormycosis, and we showed rapid and robust recruitment of phagocytes to the site of infection in vivo, spores are not cleared from zebrafish larvae over a time course of 96 h after infection, as demonstrated by CFU countings indicating live spores (P = 0.229 [n = 5], Kruskal-Wallis test). (D) We were able to show a lack of induction of reactive oxygen species (ROS) in response to fungal spores compared to the ROS-inducing stimulus PMA (P < 0.0001 [n = 9], Mann-Whitney U test), indicating a lack of antimicrobial activity. (E) Representative image of an innate granuloma formed of fungal spores and macrophages (maximum-intensity projection of fluorescent z-stack with 43 sections every 4 μm; scale bar, 100 μm). (F) Dexamethasone treatment decreases the formation of innate granulomas (P < 0.0001 [n = 61], Fisher’s exact test) while increasing hyphal formation (P < 0.0001 [n = 61], Fisher’s exact test) and the occurrence of spore dissemination.

Mucor circinelloides can be activated out of innate granulomas by immunosuppression in vivo. (A) To investigate the potential of disease activation out of innate granulomas, we selected innate granuloma-positive larvae and immersed them in dexamethasone-containing culture medium to induce immune suppression. While control larvae showed 15.4% mortality, 92.5% of larvae transferred into dexamethasone-containing medium died over the time course of this experiment. (B) Representative image showing that larvae that had succumbed to infection presented with extensive hyphal growth (scale bar, 100 μm). (C) Further microscopic examination revealed that dexamethasone resulted in reduction in innate granuloma size and onset of hyphal growth. The top panels show a representative innate granuloma in the hindbrain ventricle at 24 hpi (before onset of dexamethasone treatment) (maximum-intensity projection of fluorescence z-stack with 19 sections every 4 μm together with bright-field image and overlay, with spores [S] in cyan and macrophages [M] in red; scale bar, 100 μm). The bottom panels show the same innate granuloma at 48 hpi (24 h post-onset of dexamethasone treatment) showing hyphal formation (arrow), reduction in innate granuloma size, and dissemination of spores (asterisks) (maximum-intensity projection of fluorescence z-stack with 36 sections every 4 μm together with bright-field image and overlay, with spores in cyan and macrophages in red; scale bar, 100 μm).