'Schistosoma mansoni' excretory-secretory products from miracidium to sporocyst stage and their effects on 'Biomphalaria glabrata' defence cells
The processes through which parasites are able to survive in their susceptible host are complex and not fully understood. The platyhelminth parasite, ‘Schistosoma mansoni’, completes part of its life cycle in the snail ‘Biomphalaria glabrata’. During its intra-molluscan development, the parasite produces excretory-secretory products (ESPs), a cocktail of uncharacterised proteins and lipids. ‘Schistosoma mansoni’ ESPs may play a role in modulating snail-host immune responses. Two laboratory strains of ‘B. glabrata’ were used in this study; a schistosome-susceptible strain (NHM1742) and a schistosome-resistant strain (NHM 3017) refractory to infection. Snail haemocytes, the main type of circulating defence cells, which have similar characteristics to macrophages, were investigated. The extracellular signal-regulated kinase (ERK) signalling pathway is known to regulate defence reactions in cells. Activated ERK-like proteins were identified in ‘B. glabrata’ haemocytes using phosphor-specific anti-ERK antibodies. The phosphorylation (or activation) of ERK was reduced by 60% in susceptible snail haemocytes following ‘S. mansoni’ ESP exposure (20 [mu]g/ml for 1 h). In contrast, resistant snail haemocytes did not exhibit any changes in phosphorylated ERK levels following ESP-challenge. Nitric oxide (NO), a reactive molecule, which plays a role in host defence mechanisms, increased 3.3 fold in resistant snail haemocytes when challenged with ESPs. ESP-challenged susceptible snail haemocytes did not show any significant modulation in NO levels. The use of scanning electron microscopy also highlighted an increase in haemocyte spreading (on glass coverslips) in ESP-challenged haemocytes from resistant snails only. Heat shock protein 70 (HSP70), an evolutionarily conserved protein with immune-modulation properties was investigated using western blotting and scanning confocal microscope using anti-HSP70 antibodies. HSP70 was significantly reduced in susceptible (P[less than or equal to]0.01) and resistant (P[less than or equal to]0.05) snail haemocytes following 1 h exposure to 20 [mu]g/ml ESPs. Interestingly, the ERK cell signalling pathway was found to coordinate both NO and HSP70 levels, as the ERK inhibitor, U0126, significantly reduced levels NO output and HSP70 expression in ‘B. glabrata’ haemocytes. Finally, haemocyte gene expression was analysed after ESP-challenge using a ‘B. glabrata’ cDNA microarray. The microarray analysis highlighted differentially expressed genes (DEGs) between ESP exposed resistant and susceptible snail haemocytes. These DEGs transcribe proteins involved in protein degradation, protein transcription, cell-to-cell interaction and immune responses. This study has broadened our knowledge on the differences that exist between resistant and susceptible ‘B. glabrata’ haemocytes and their differential response to ‘S. mansoni’ ESPs; providing important insights into snail-schistosome interactions.