PHARMACOLOGICAL ANALYSIS OF NEUTROPHIL CHEMOTACTIC FACTOR PRODUCTION BY LEUKOCYTES AND ROLES OF PAF IN ALLERGIC INFLAMMATION IN RATS

1 The role of platelet activating factor (PAF) in neutrophil infiltrat ion in air pouch type allergic inflammation in rats was investigated. 2 Neutrophil infiltration into the pouch fluid 8 h after injection of the antigen (azobenzenearsonate-conjugated acetyl bovine serum albumin ) solution into the air pouch of immunized rats was inhibited dose-dep endently by treatment with PAF antagonists (CV-3988, L-652,731 and Y-2 4,180) in parallel with the decrease in neutrophil chemotactic activit y in the pouch fluid. 3 Four hours after injection of the antigen solu tion into the air pouch of immunized and nonimmunized rats, there was no significant difference between the two groups in the number of tota l leucocytes, neutrophils, mononuclear cells and eosinophils in the po uch fluid. However, when the infiltrated leucocytes were incubated in medium, chemotactic factor production by leucocytes from immunized rat s was greater than that from non-immunized rats. 4 When leucocytes fro m non-immunized rats were preincubated for various periods in the medi um containing 10 or 50 nM of PAF, washed, and further incubated in the medium containing no PAF, chemotactic factor production was not stimu lated. 5 The increase in the chemotactic activity in the conditioned m edium was not suppressed by the 5-lipoxygenase inhibitor, AA861. In ad dition, the chemotactic activity in the conditioned medium was not inh ibited by the PAF antagonists. 6 Incubation of the infiltrated leucocy tes in the medium containing the protein synthesis inhibitor, cyclohex imide, inhibited chemotactic factor production in a concentration-depe ndent manner in parallel with the decrease in uptake of [H-3]-leucine into the acid-insoluble fraction of leucocytes. 7 Separation of the ch emotactic activity in the conditioned medium by isoelectric focusing r evealed that the leucocyte infiltrated into the pouch fluid produce tw o kinds of factors, viz. leucocyte-derived neutrophil chemotactic fact or-1 (LDNCF-1) and LDNCF-2 of which pI values are 4-5 and above 8, res pectively. 8 The results indicate that PAF has no significant role in leucocyte activation to produce chemotactic factors, and that neutroph il chemotactic factors produced by infiltrated leucocytes are not PAF or leukotriene B4 but are produced through a protein synthesis mechani sm. 9 The mechanism of action of PAF antagonists on neutrophil infiltr ation into the inflammatory locus is discussed.