Sex differences in a murine model of infective endocarditis

Abstract

Infective endocarditis (IE) is a highly lethal disease with a notable male predominance, yet the biological basis for this sex disparity remains unclear. We established a murine IE model in C57BL6 mice in which aortic valve injury was induced via wire-injury and followed by intravenous injection of Staphylococcus aureus. Infection was confirmed by blood and valve cultures, and cardiac function was evaluated by echocardiography. Systemic cytokine levels were measured, and immune cell infiltration in valve tissue was assessed by flow cytometry and immunofluorescence. In the murine model, IE was induced in 77/85 animals. Male mice exhibited significantly higher bacterial loads in blood and valves, greater valve cusp enlargement, increased ventricular volumes, and more frequent aortic regurgitation. Both sexes showed strong neutrophilic responses, but males had markedly elevated systemic IL-1α, IL-1β, IL-6, and TNF-α levels. Females demonstrated earlier and more robust recruitment of CD68⁺ and CD206⁺ macrophages, as well as Ly6G⁺ neutrophils, to the injured valve, correlating with reduced bacterial vegetations. This murine model mirrors the clinical sex disparity in IE: males develop more severe disease and systemic inflammation, while females benefit from a rapid, localized immune response. These findings provide a platform for dissecting molecular drivers of sex-specific susceptibility in IE.

Keywords: Immune response; Infective endocarditis; Murine model; Sex differences; Staphylococcus aureus; Valve inflammation.

Fig. 1

Gender Analysis of Infective Endocarditis. A Efficacy of IE induction in female and male mice. (B) Bacteremia in murine IE model was assessed 24 h after bacterial injection and was more prevalent in male than female mice, correspondingly valvular bacterial infiltration was increased in male mice as well (C). Data is presented as mean ± SEM. *P < 0.05. CFU colonies forming units, IE infective endocarditis

Fig. 2

Valvular and myocardial changes in murine IE model. Transthoracic echocardiography was performed at baseline and day 7 after bacterial challenge. Aortic valve cusp diameter (A) and aortic valve regurgitation (B) are indirect parameters of IE severity. (C) Exemplary image of aortic valve vegetation (red arrows) in parasternal long axis view. To assess valvular and myocardial changes, ventricular volumes and left-ventricular ejection fraction, aortic peak velocity, heart rate and cardiac output (D–I) were measured. Data is presented as mean ± SEM, **P < 0.01; *P < 0.05

Fig. 3

Plasma cytokine levels following IE induction. Cytokines were measured on day 1, day 3 and day 7 after bacterial challenge. The pro-inflammatory cytokines IL-1α (A), IL-1β (B), IL-6 (C), TNF-α (D) were increased in male mice compared to females after bacterial challenge. While circulating levels of the anti-inflammatory cytokine IL-10 (E) rose over time it was consistently lower in male mice. Data are presented as mean ± SEM. ***P < 0.001; **P < 0.01; *P < 0.05

Fig. 4

Immune cell infiltration of the aortic valve. Aortic valve cross sections were obtained immediately after sacrifice. Valvular vegetation area was assessed using Gram staining (A). Valvular immune cell infiltration was analyzed using immunofluorescence microscopy after CD45 (B), Ly6G (C), CD68 (D) and CD206 (E) staining day 1, day 3 and day 7 after bacterial challenge. Data is presented as mean ± SEM, and statistical significance was determined using unpaired/paired one-way ANOVA. ***P < 0.001; **P < 0.01; *P < 0.05. BC bacterial challenge, WI wire-injury