Fig. 3

Sialic acid exacerbates gut dysbiosis-induced mastitis in mice. A Experimental protocol of the sialic acid treatment. Mice were treated with free water, Neu5Ac, ampicillin or ampicillin + Neu5Ac for the indicated times. The mammary tissues were harvested 14 days after parturition. B Histological analysis of mammary tissues using H&E-stained sections (scale bar, 20 μm). Red arrows indicate leukocyte infiltration. C Histological scores of mammary gland in different groups based on H&E-stained sections (n = 7–8). Inflammatory parameters of mammary glands from different groups, including TNF-α (D) and IL-1β (E) concentrations and MPO activity (F), were measured (n = 7–8). Representative protein levels of ZO-1, Occludin and Claudin-3 (G) and intensity analysis of ZO-1, Occludin, and Claudin-3 from different treated mice (H-J) were determined (n = 4). Data are expressed as the mean ± SD (C–F and H–J). One-way ANOVA was performed, followed by Tukey test (C–F and H–J). *p < 0.05, **p < 0.01, ***p < 0.001 indicate significant difference. A, ampicillin; C, control; N, Neu5Ac; AN, ampicillin + Neu5Ac