The biologic significance of neutrophil regulatory mechanisms

Neutrophil killing of single microorganisms as measured by a new method

A new method of measuring polymorphonuclear leukocyte (PMN) microbicidal activity was developed in which single colony forming units of Staphylococcus aureus were isolated in microtiter wells with or without PMN, centrifuged, and incubated overnight. The percentage of bacteria killed was determined by comparing the number of PMN-containing wells showing bacterial growth to PMN-free controls. This percentage was positively correlated with the number of PMN in each well and was reduced if plates were not centrifuged or if cytochalasin B was added. Killing of either S. aureus or Escherichia coli was enhanced using fresh serum activated by prior exposure to large numbers of E. coli. There was no enhancement using heated serum that had been exposed to E. coli, nor was there enhancement when S. aureus was preopsonized by exposure to fresh serum. This assay circumvents problems in assessing microbicidal activity where aggregation of organisms might otherwise be an issue.

Bacteria-phagocyte interactions: Fusobacterium-induced secretion of a neutrophil self-regulatory factor

Direct interaction between Fusobacterium nucleatum and human neutrophils resulted in the secretion of a neutrophil self-regulatory factor(s). The secretion of this factor was bacteria specific, and depended on the integrity of the bacteria cell surface. Factor secretion occurred within 15 min of bacteria--neutrophil interaction. Pre-treatment of neutrophils with cytochalasin B but not sodium fluoride inhibited factor secretion. The factor was sensitive to trypsin and heat treatment. Ultrafiltration experiments showed that it has a molecular weight between 10,000 and 30,000 daltons. Its biologic role may be that of a molecular mediator for the recruitment of resting neutrophils so as to amplify the immunological and inflammatory response.