Leucocyte recruitment induced by type II phospholipases A 2 into the rat pleural cavity

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Bothropstoxin-I (BthTX-I) and bothropstoxin-II (BthTX-II) are Lys-49 and Asp-49 phospholipases A 2 (PLA 2s), respectively, isolated from Bothrops jararacussu venom. Piratoxin-I (PrTX-I) is a Lys-49 PLA 2 isolated from Bothrops pirajai venom. In this study, the ability of BthTX-I, BthTX-II and PrTX-I to recruit leucocytes into the rat pleural cavity and potential mechanisms underlying this effect were investigated. Intrapleural injection of either BthTX-I or PrTX-I (10–100 μg/cavity each) caused a significant leucocyte infiltration at 12 h after injection. The maximal cell migration was observed with the dose of 30 μg/cavity (14.9±15.5 and 17.6±1.6×10 6 cells/cavity, respectively). Leucocyte counts consisted mainly of mononuclear cells, but significant amounts of neutrophils and eosinophils were also observed. Intrapleural injection of BthTX-II (10–100 μg/cavity) caused a marked leucocyte infiltration at 6 and 12 h after injection. The maximal response was observed with the dose of 100 μg/cavity (57.3±3.4×10 6 cells/cavity, 6 h). The leucocyte counts were mainly composed of neutrophils and mononuclear cells. The treatment of either BthTX-I (30 μg/cavity, 12 h) or BthTX-II (30 μg/cavity, 6 h) with the PLA 2 inhibitor p-bromophenacyl bromide ( p-BPB) had no effect on the total and differential leucocyte counts induced by these proteins. The same treatment partially reduced the PrTX-I-induced pleural leucocyte infiltration. In rats depleted of the histamine and 5-hydroxytryptamine (5-HT) stores by chronic treatment with compound 48/80, the total leucocyte counts in response to BthTX-I, BthTX-II and PrTX-I was not significantly affected compared to control animals. In addition, BthTX-I, BthTX-II and PrTX-I (100 μg/ml each) significantly degranulated pleural mast cells in vitro leading to the release of [ 14C]5-hydroxytryptamine ([ 14C]5-HT). p-BPB and heparin (50 IU/ml) significantly reduced the [ 14C]5-HT release induced by these PLA 2s. Our results demonstrate that BthTX-I, BthTX-II and PrTX-I recruit leucocyte into the pleural cavity of the rat by mechanisms unrelated to enzymatic activity and pleural mast cell degranulation.