Pharmacological analysis of neutrophil chemotactic factor production by leucocytes and roles of PAF in allergic inflammation in rats

The role of platelet activating factor (PAF) in neutrophil infiltration in air pouch type allergic inflammation in rats was investigated. 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‐dependently by treatment with PAF antagonists (CV‐3988, L‐652,731 and Y‐24,180) in parallel with the decrease in neutrophil chemotactic activity in the pouch fluid. Four hours after injection of the antigen solution into the air pouch of immunized and non‐immunized rats, there was no significant difference between the two groups in the number of total leucocytes, neutrophils, mononuclear cells and eosinophils in the pouch fluid. However, when the infiltrated leucocytes were incubated in medium, chemotactic factor production by leucocytes from immunized rats was greater than that from non‐immunized rats. When leucocytes from non‐immunized rats were preincubated for various periods in the medium containing 10 or 50 nM of PAF, washed, and further incubated in the medium containing no PAF, chemotactic factor production was not stimulated. The increase in the chemotactic activity in the conditioned medium was not suppressed by the 5‐lipoxygenase inhibitor, AA861. In addition, the chemotactic activity in the conditioned medium was not inhibited by the PAF antagonists. Incubation of the infiltrated leucocytes in the medium containing the protein synthesis inhibitor, cycloheximide, inhibited chemotactic factor production in a concentration‐dependent manner in parallel with the decrease in uptake of [³H]‐leucine into the acid‐insoluble fraction of leucocytes. Separation of the chemotactic activity in the conditioned medium by isoelectric focusing revealed that the leucocyte infiltrated into the pouch fluid produce two kinds of factors, viz. leucocyte‐derived neutrophil chemotactic factor‐1 (LDNCF‐1) and LDNCF‐2 of which pI values are 4–5 and above 8, respectively. The results indicate that PAF has no significant role in leucocyte activation to produce chemotactic factors, and that neutrophil chemotactic factors produced by infiltrated leucocytes are not PAF or leukotriene B₄ but are produced through a protein synthesis mechanism. The mechanism of action of PAF antagonists on neutrophil infiltration into the inflammatory locus is discussed. 1994 British Pharmacological Society