Neutrophil activity in abscess-bearing mice: comparative studies with neutrophils isolated from peripheral blood, elicited peritoneal exudates, and abscesses

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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.