The accumulation of 111In-eosinophils induced by inflammatory mediators, in vivo

Eosinophils are implicated in the pathogenesis of a variety of allergic inflammatory diseases such as asthma. Several substances have been shown to be chemotactic for eosinophils in vitro, but the inflammatory mediators involved in the accumulation of eosinophils in vivo are as yet unidentified. In this study we have developed a system to measure the accumulation of 111In-eosinophils in guinea-pig skin in vivo. Horse serum-induced guinea-pig peritoneal eosinophils were radiolabelled with 111In and injected intravenously into recipient animals. 125I-albumin was also injected intravenously in order to measure local oedema formation simultaneously. A range of putative mediators was injected intradermally and responses measured for up to 2 hr. Of the mediators tested, guinea-pig C5a des Arg in zymosan-activated plasma was the most active. Recombinant human C5a (rHC5a) was also highly active, but less than the guinea-pig material. C5a des Arg in maximally activated plasma induced a 1500% increase in eosinophil accumulation, while rHC5a (10(-10) mol dose) induced a 600% increase. Platelet-activating factor (PAF) and leukotriene B4 (LTB4) were also tested for comparison. With respect to 111In-eosinophil accumulation, the order of potency of the mediators tested was as follows: guinea-pig C5a des Arg greater than LTB4 greater than PAF. In contrast, the order of potency of the mediators with respect to oedema formation was: PAF greater than guinea-pig C5a des Arg greater than LTB4. The techniques described will facilitate analysis of the mechanisms involved in eosinophil accumulation in defined inflammatory reactions.