Bacterial formyl peptide mediated chemotaxis and extracellular acidification in shrimp haemocytes

The bacterial formyl peptide N-formylmethionine-leucine-phenylalanine (fMLP ) is a potent chemoattractant for mammalian neutrophils. In this study, we demonstrated the binding of fluorescent dye-conjugated-fMLP to haemocytes o f the penaeid shrimp Penaceus penicillatus (Alcock), through the use of flo w cytometry. Fluorescence microscopy with rhodamine-fMLP suggested that fML P receptors are present only in sub-populations of the haemocytes: granuloc ytes and the semi-granular cells. In addition, fMLP dose-dependently mediat ed chemotaxis in sub-populations of haemocytes. Microphysiometry experiment s demonstrated rapid extracellular acidification upon addition of fMLP, whi ch is in agreement with the observation in neutrophils. t-BOC, the specific fMLP receptor antagonist, was able to block the binding, chemotaxis and ex tracellular acidification induced by the peptide. The ability of shrimp hae mocytes to migrate toward fMLP in vitro suggests that this mechanism map be important for the accumulation of these cells in infected tissues of the s hrimps. (C) 2001 Elsevier Science Ltd. All rights reserved.