BRIDGING OF NEUTROPHILS TO TARGET-CELLS BY OPSONIZED ZYMOSAN ENHANCESTHE CYTOTOXICITY OF NEUTROPHIL-PRODUCED H2O2

Hydrogen peroxide (H2O2) is a well-established cytotoxic agent release d by activated neutrophils into the extracellular environment, However , a maximum of only 5 mu M H2O2 was detected in the medium when 10(6) neutrophils/ml were activated with opsonized zymosan (OZ), more than 5 0-fold lower than the concentration of exogenous H2O2 required to prod uce equivalent killing of a cell line, In addition PMA-activated neutr ophils were noncytotoxic, despite the capacity of PMA to generate two- to fourfold as much H2O2 for five times longer, The basis for this di screpancy was explored, NaN3 increased cytotoxicity to > 90% only when neutrophils were activated with OZ due in part to inhibition of myelo peroxidase-mediated hydrolysis of H2O2, while catalase completely prev ented cytotoxicity of OZ-activated neutrophils, These results indicate that H2O2 was solely responsible for the observed cytotoxicity. OZ-me diated cytotoxicity was prevented by intermittent agitation of the cul tures or by the addition of soluble complement receptor type 1, sugges ting that a physical association between neutrophils and target cells mediated by OZ was required to generate a cytotoxic environment, Signi ficant numbers of neutrophil-target cell aggregates were observed by m icroscopic examination only under low hydrodynamic shear conditions, W e conclude that the cytotoxic potency of H2O2 produced by neutrophils activated with OZ was due to a localized high concentration of H2O2 to which the target cells were exposed as a result of their labile adher ence to OZ, This phenomenon may reflect a mechanism that neutrophils h ave acquired for maximizing the antimicrobial power of extracellular o xidants toward microbes that escape phagocytotosis.