Related Experiment Videos
Neutrophil activity in abscess-bearing mice: comparative studies with neutrophils isolated from peripheral blood,
Abstract:
Intraabdominal abscesses were induced in mice by intraperitoneal inoculation of Bacteroides fragilis and Escherichia coli plus bran as the abscess-potentiating agent. Six- or seven-day-old abscesses were mechanically disaggregated in buffer, and the cells obtained were fractionated on discontinuous Percoll density gradients. Neutrophil populations of different density, each approximately 90% pure, were isolated. When the abscess-derived neutrophils were subsequently incubated with normal serum in vitro under aerobic conditions, the viability of the gram-negative bacteria that had been phagocytosed within the abscess did not change significantly. This anergy to intracellular bacteria (on subsequent incubation in vitro under optimal conditions for phagocytic killing) was also found for neutrophils that had been obtained from abscesses induced by a mixture that included Proteus mirabilis plus B. fragilis and from those induced by E. coli plus P. mirabilis. While unable to significantly kill intracellular organisms that had been phagocytosed in vivo, the abscess-derived neutrophils could engulf and kill organisms to which they were exposed in vitro. Neutrophils from abscesses induced by P. mirabilis only plus bran killed that organism introduced in vitro significantly more effectively than the organisms that had been engulfed in vivo. In contrast, neutrophils from abscesses induced by the gram-positive organism Staphylococcus aureus plus bran were able to kill their intracellular organisms on subsequent incubation in vitro as effectively as they could kill added S. aureus. Neutrophils isolated from the peripheral blood and from induced peritoneal exudates of abscess-bearing mice were able to phagocytose and kill organisms in vitro with greater efficiency than abscess-derived neutrophils. The mechanism whereby neutrophils from abscesses induced by the gram-positive organism S. aureus can kill the organisms phagocytosed in vivo on subsequent in vitro incubation, in contrast to the relative anergy to their intracellular organisms displayed by neutrophils derived from abscesses induced by combinations of gram-negative bacteria, is not known.
Insights
Neutrophils from intraabdominal abscesses struggle to kill bacteria previously phagocytosed within the abscess. However, these neutrophils can kill bacteria introduced in vitro, unlike neutrophils from Staphylococcus aureus abscesses which retain killing ability.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Intraabdominal abscesses are complex infections involving polymicrobial communities.
- Neutrophils are critical immune cells for combating bacterial infections.
- Understanding neutrophil function within abscess environments is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the phagocytic and killing capacity of neutrophils isolated from experimentally induced intraabdominal abscesses.
- To compare the function of neutrophils derived from gram-negative versus gram-positive bacterial abscesses.
- To assess the impact of the in vivo abscess environment on neutrophil antimicrobial activity.
Main Methods:
- Intraabdominal abscesses were induced in mice using combinations of Bacteroides fragilis, Escherichia coli, Proteus mirabilis, and Staphylococcus aureus with bran.
- Neutrophils were isolated from abscesses using Percoll density gradients.
- Neutrophil function was assessed by measuring their ability to phagocytose and kill bacteria in vitro, both those phagocytosed in vivo and those introduced in vitro.
Main Results:
- Neutrophils from gram-negative bacterial abscesses showed impaired killing of intracellular bacteria phagocytosed in vivo but retained in vitro killing capacity.
- Neutrophils from Staphylococcus aureus abscesses maintained their ability to kill intracellular bacteria in vitro.
- Peripheral blood neutrophils and exudate neutrophils from abscess-bearing mice exhibited greater phagocytic and killing efficiency than abscess-derived neutrophils.
Conclusions:
- Neutrophils within gram-negative abscesses exhibit functional anergy towards intracellular bacteria acquired in vivo.
- Neutrophils from gram-positive abscesses retain antimicrobial activity against intracellular bacteria.
- The abscess microenvironment significantly impacts neutrophil function, with implications for therapeutic strategies.