Staphylococcus aureus induced trained immunity in macrophages confers heterologous protection against gram-negative bacterial infection

Staphylococcus aureus can induce trained immunity in murine macrophages offering protection against repeat exposure during S. aureus skin infection. Here we demonstrate that S. aureus exposure can result in non-specific trained immunity in humans and mice, enhancing macrophage responsiveness and bacterial clearance in a heterologous challenge. In humans, the enhanced macrophage responsiveness was accompanied by metabolic changes and histone modification. In mice, the enhanced responsiveness of macrophages occurred in conjunction with enhanced myelopoiesis. This report provides further insights on the host's response to the bacterium S. aureus, indicating that exposure to this organism induces heterologous protection against subsequent gram-negative infection that is provided by macrophages. These findings support the hypothesis that S. aureus has evolved to develop a mutualistic relationship with the host, imbuing the host with enhanced capacity to protect itself from attack by alternative pathogens, while potentially allowing S. aureus to exert its dominance within its niche.