Macrophage depletion enhances gut dysbiosis and severity in sepsis mouse model

Abstract

Macrophage is vital players in the responsiveness of the innate immune system against injury or infection. Although macrophage depletion is well-known for some emerging therapies, such as osteoporosis, osteopenia, and decreasing tumor-associated macrophages in melanoma, dysfunction of macrophages leads to an inability of an appropriate immune response and implicated in various disease processes, especially intestinal macrophages that play a key role in the gut immune system and the regulation of gastrointestinal physiology. To obtain an understanding of the role of sepsis-associated macrophages, clodronate was used for the dysfunction of mouse macrophages with and without cecal ligation and puncture (CLP) sepsis. Macrophage depletion significantly increased fecal Ascomycota, with a slight growth of bacterial microbiota which might be enhanced gut-barrier damage as Candida pintolopesii, Klebsiella pneumoniae, Acinetobacter radioresistens, and Enterococcus faecalis that were identified from mouse blood. In addition, increased mortality, cytokine overproduction, organ damage (liver and kidney), gut leakage (FITC-dextran), imbalance of fecal fungi and pathogenic bacteria, as well as fungemia and bacteremia in sepsis with macrophage-depleted animals was more severe than sepsis in control mice (fungemia and bacteremia). To determine the interaction between fungal molecules and bacterial abundance, each heat-kill lysate of C. pintolopesii, C. albicans ATCC90028, C. albicans (isolated from human blood), and purified (1→3)-β-D-Glucan (BG), a major component of the fungal cell wall was co-cultured with each pathogenic bacterium, including K. pneumoniae, E. faecalis, and A. radioresistens, indicating that the enhanced growth of bacteria that were isolated from the blood implying a direct enhancer to some bacterial species. Furthermore, the additive effect of heat-kill lysate Candida yeast cells or their components together with heat-kill lysate of isolated bacteria on enterocytes (Caco-2) also supported an influence of gut fungi in worsening sepsis. In conclusion, macrophage depletion enhanced fecal Candida and fecal pathogenic bacteria overgrowth, intestinal barrier damage, and gut translocation of bacteria and fungi that additively worsened sepsis severity. These findings suggested that fecal fungus could spontaneously elevate in response to macrophage-depleted therapy, increasing the severity of sepsis.