Bacterial lipopolysaccharide modulates protein kinase C signalling in Lymnaea stagnalis haemocytes

Our knowledge of cell signalling pathways in the molluscan immune system and their response to immunological challenge is currently poor. The present study focused on the Protein Kinase C (PKC) pathway in the immune cells (haemocytes) of Lymnaea stagnalis and its response following exposure to bacterial lipopolysaccharide (LPS). Western blotting of haemocyte proteins with either anti-PKC (pan) or anti-phospho-PKC (Ser 660) antibodies revealed the presence of two PKC-like immuno-reactive proteins of approximately 76 and 85 kDa. Challenge of haemocytes with LPS transiently increased the phosphorylation of the 85 kDa isoform, with a 2.2-fold increase in phosphorylation levels at 5 min and a return to basal levels after 20 min. This LPS-mediated response was blocked following treatment of haemocytes with GF109203X. PKC activities measured in anti-phospho-PKC immunocomplexes following haemocyte treatment with LPS and GF109203X correlated well with the observed PKC phosphorylation levels. These data show for the first time that the activity of the PKC pathway in molluscan immune cells is modulated by LPS, as it is in mammals, and suggest that cell signalling in the innate immune response may have been conserved through evolution.