Influence of interleukin 1 alpha on superoxide anion, platelet activating factor release and phospholipase A(2) activity of naive and sensitized guinea-pig alveolar macrophages

1 We studied the effect exerted by hr-interleukin-1 alpha (IL-1 alpha) on responsiveness of alveolar macrophages (AM) from naive and sensitized guinea-pigs, through O-2(radical anion) production (by ferricytochrome C reduction), platelet-activating factor (PAF) release (by platelet aggregation), prostaglandin E-2 (PGE(2)) release (by a radioimmunoassay), and cytosolic phospholipase A(2) (cPLA(2)) activity (by hydrolysis of radioactive substrate). 2 In naive guinea-pig AM, 0.06 nM hr-IL-1 alpha pretreatment decreased by 65% O2(radical anion) release stimulated with 10 nM fMLP. In contrast, O2(radical anion) production was not affected in sensitized guinea-pig AM. 3 O2(radical anion) release elicited by fMLP stimulation in both cell groups was affected by PLA(2) inhibitors (10 mu M bromophenacyl bromide, BPB or 10 mu M methylprednisolone, MP). In contrast, 10 mu M arachidonyl trifluoromethyl ketone (AACOCF(3)), a cPLA(2) inhibitor, was ineffective. 4 In naive AM, PAF release was elicited by hr-IL-1 alpha pretreatment and by separate fMLP-stimulation, but when the stimulus was added to hr-IL-1 alpha-pretreated cells inhibition of PAF release was observed. In sensitized AM, PAF release was lower than that found in naive guinea-pig AM in both hr-IL-1 alpha-pretreated and fMLP-stimulated cells. 5 PGE(2) release was unaffected by hr-IL-1 alpha pretreatment and it was decreased by fMLP in both naive and sensitized AMs. The latter released less PGE(2) than naive cells in basal conditions and after fMLP treatment. 6 Sensitized AM showed a greater cPLA(2) activity in all experimental conditions in comparison to naive cells. cPLA(2) activity assayed in the cytosolic fraction was found to be enhanced by hr-IL-1 alpha pretreatment and by fMLP stimulation in naive but not in sensitized AM. However, when the stimulus was added to hr-IL-1 alpha-pretreated cells we observed a decrease in cPLA(2) activity in the cytosol and an increase in the membranes, thus suggesting a translocation of enzymatic activity. 7 In conclusion, hr-IL-1 alpha can modulate the responsiveness of AM from naive and sensitized guineapigs, as suggested by changes found in the release of PAF and O-2(radical anion) and in cPLA(2) activity; therefore, sensitization itself may affect cellular responsiveness.