Exocytosis of the prophenoloxidase activating system from crayfish haemocytes

Abstract

Lipopolysaccharides (LPS) and the β-1,3-glucan laminarin G, both of which specifically activate the prophenoloxidase (proPO) activating system of crayfish haemocyte lysate, were found to induce degranulation (exocytosis) and subsequent lysis in vitro of monolayers of semigranular haemocytes from the crayfish,Pacifastacus leniusculus, (Table 1, Fig. 1 b), whereas the granular cells were unaffected (Fig. 1 c). Exocytosis of isolated semigranular or granular cells in vitro could also be evoked by the Ca2α ionophore A23187 (Table 2, Fig. 1 d). In this case, the whole proPO system was released from the cellular vesicles in its inactive form, since the secreted material contained protease and prophenoloxidase as inactive proenzymes, which could be activated if LPS or β-1,3-glucans were added (Table 3). The anion channel blocker SITS, which inhibits exocytosis in several systems, prevented degranulation triggered by β-1,3-glucan, LPS, or ionophore. It is concluded that, in arthropods, LPS serve as an indicator of Gram negative bacteria and β-1,3-glucan as an indicator of fungi. These non-self molecules elicit both the exocytotic release of the proPO system from the semigranular cells and the subsequent biochemical activation of this system.