Differing antimicrobial potency and specificity of peripheral blood and autologous exudative polymorphonuclear...

Little is known about the antimicrobial potency and specificity of polymorphonuclear leucocytes which actually appear at the sites of bacterial invasion in tissues. In the present work we have compared inflammatory leucocytes induced by intraperitoneal injection of casein in rabbits with autologous peripheral blood cells in killing Escherichia coli serotype 01 and Staphylococcus aureus 502A. The results indicate that inflammatory leucocytes differ significantly from their virgin blood ancestors. While the blood leucocytes were only able to suppress the growth of the gram-negative bacteria, autologous exudative cells killed more than 95% of the test organisms within 1 h of incubation at 37 degrees C. The enhanced microbicidal activity of the inflammatory cells however, was only specific for the gram-negative bacteria, as evidenced by the failure of leucocytes to kill Staph. aureus to the same extent as the peripheral blood cells. In association with the enhanced gram-negative microbicidal activity the inflammatory cells produced chemiluminescence and released two to three times more O2-anions than the peripheral cells. We interpret these observations to mean that chemotactic factors such as casein activate inflammatory cells to increase their oxidative metabolism. Since microbicidal action of leucocytes is thought to proceed in part through oxygen-dependent reactions, the inflammatory leucocytes would be expected to effectively kill bacteria that are highly susceptible to these lethal oxygen metabolites. It cannot therefore be assumed that assessment of the functional capacity of the virgin peripheral blood PMNs would provide information on the functional characteristics of activated leucocytes which actually migrate to and accumulate at inflammatory sites.