Dexamethasone treatment leads to disruption of the granuloma structure, increase in the number of granulomas and loss of hypoxia in zebrafish with a latent mycobacterial infection. (A) Ziehl–Neelsen staining (ZN) of mycobacteria (purple). Black arrowheads indicate the outline of a granuloma. Trichrome staining (TC) of fibrous tissue around granulomas (blue) (black arrows). (B) Quantification of the total number of granulomas and the proportion of necrotic and non-necrotic granulomas (left), and the number of nascent granulomas and sites with non-capsulated mycobacteria (right) per fish after 4, 14 and 21 days of dexamethasone treatment or normal feeding (n=3-6 fish/group). Data are presented as mean±s.d. Statistical significance was assessed by unpaired Student's t-test. (C) Hypoxic staining shows hypoxic lesions inside granulomas in dark brown (pink stars). The proportions of hypoxic and non-hypoxic granulomas during a latent infection, and after 2 weeks of dexamethasone treatment, are quantified in the pie chart. See also Fig. S2.

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.

Schematic representation of the experimental protocol for testing vaccine candidates against the reactivation of a latent mycobacterial infection. Fish with a latent M. marinum infection are immunized with a DNA plasmid carrying a GFP-tagged mycobacterial antigen, which allows detection of successful immunizations by fluorescent microscopy. After 5 weeks, the fish are subjected to dexamethasone treatment (10 μg/fish/day) for 4 weeks, followed by determination of bacterial burdens by qPCR.

Dexamethasone treatment increases the number of multicentric granulomas and the relative proportion of necrotic granulomas.

(A) Classification of different types of granulomas with Ziehl-Neelsen staining used for the quantification in Figure 2 and in this figure. (B) Quantification of multicentric granulomas per fish in a latent infection compared to a dexamethasone treatment. The bars shows mean±s.d. (n=3-6 fish/group). (C) The proportion of necrotic and non-necrotic granulomas in a latent infection and after dexamethasone treatment (n=3-6 fish/group). Bars show the mean percentage±s.d. p values are calculated with two-way ANOVA.