In the present study we investigated the role of platelet-activating factor (PAF) and interleukin-6 (IL-6) in delaying polymorphonuclear neutrophil (PMN) apoptosis. Isolation of PMN was performed by using the discontinuous plasma-Percoll gradient technique. PMN was cultured in enriched RPMI 1640 media at 2 x 10(7) PMN/ml for 24 h. Subgroups were treated with IL-6 or PAF or pretreated with PAF receptor antagonist BN52021 before IL-6 or PAF were added. Morphological assessment and quantitation of apoptosis were performed with acrodine/ethidium bromide stain and epifluorescent microscope. The results showed that both IL-6 and PAF suppressed PMN apoptosis. Pretreatment of PMN with BN52021 abrogated the effects of IL-6 and PAF. It is suggested that PAF may be a crucial cytokine in the suppression of PMN apoptosis. These observations may contribute to elucidating the mechanisms of IL-6 and PAF in mediating postinjury hyperinflammation and secondary organ dysfunction and provide a clue for the prevention and treatment of the conditions.