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Role of the macrophage in the translocation of intestinal bacteria
Abstract:
To clarify the role of the macrophage in the translocation of intestinal bacteria, groups (n = 10) of Swiss Webster mice (Immunocompetent) and C3H/HeJ mice (macrophage defective) were given bacitracin/streptomycin in their drinking water to eliminate the majority of the intestinal microflora. These mice were then "monoassociated" with a streptomycin-resistant strain of Escherichia coli. Forty-eight hours later, E coli was present in all animals at a concentration of 10(11)/g of cecum. In four separate experiments, E coli was recovered from 100% of the mesenteric lymph nodes (MLNs) of the immunocompetent Swiss Webster mice and from 10%, 40%, 30%, and 50% of the MLNs of macrophage-defective C3H/HeJ mice. Swiss Webster mice were then similarly monoassociated by antibiotic decontamination followed by administration of antibiotic-resistant, fluorescein-labeled E coli in their drinking water; cohort groups of mice were given fluorescein-labeled latex beads (1 micron in diameter) in their drinking water. Two, four, and 11 days later, the MLNs were removed and single cell suspensions were analyzed in the fluorescence-activated cell sorter. The fluorescein label was detected exclusively in the macrophage (esterase-positive) population. These results support the hypothesis that intestinal macrophages may play a key role in the transport of intestinal particles (including bacteria) into extraintestinal sites.
Insights
Intestinal macrophages are key to bacterial translocation. In mice, these immune cells, identified via fluorescence, were found to transport E. coli from the gut to lymph nodes, supporting their critical role.
Area of Science:
- Immunology
- Gastroenterology
- Microbiology
Background:
- The translocation of intestinal bacteria across the gut barrier is a critical process in host-microbe interactions.
- Macrophages are immune cells present in the intestinal lining, but their specific role in bacterial translocation remains unclear.
Purpose of the Study:
- To investigate the role of intestinal macrophages in the translocation of bacteria from the gut to mesenteric lymph nodes (MLNs).
Main Methods:
- Mice models (Immunocompetent Swiss Webster and macrophage-defective C3H/HeJ) were used.
- Intestinal microflora was eliminated using antibiotics, followed by mono-association with Escherichia coli.
- Fluorescein-labeled E. coli and latex beads were administered, and MLNs were analyzed using fluorescence-activated cell sorting.
Main Results:
- E. coli was recovered from 100% of MLNs in immunocompetent mice, compared to significantly lower rates in macrophage-defective mice.
- Fluorescein-labeled E. coli and latex beads were exclusively detected within the macrophage population in MLNs.
- These findings demonstrate a direct role for macrophages in particle transport from the intestine.
Conclusions:
- Intestinal macrophages play a significant role in the transport of intestinal bacteria and other particles to extraintestinal sites.
- Understanding this mechanism is crucial for addressing conditions involving bacterial translocation and gut barrier integrity.