A functional analysis of the haemocyte phagocytosis of clam Ruditapes philippinarum
The immune system of Ruditapes philippinarum is non-specific,and the haemocytes play an important role in its immune defense.In this study,the morphology and structure of Escherichia coli,Staphylococcus aureus and Vibrio anguillarum were observed under scanning electron microscopy and transmission electron microscopy,and then the phagocytosis of haemocytes on these bacteria was com-pared and observed under light microscopy and transmission electron microscopy(TEM).The results showed that E.coli was rod-shaped,with an average size of 1.6×0.6 μm;S.aureus was spherical in shape,with an average size of 1.3×1.1 μm,and arranged in a grape string;V.anguillarum was arc-shaped,with a single slender polar flagellum,the average size was 1.3×0.7 μm,and the average fla-gellum length was 4.5 μm.The phagocytosis rate of E.coli,S.aureus and V.anguillarum was 38.7％,30.0％and 24.4％,respectively.TEM observation found that the haemocytes can adhere and wrap the bacteria through filopodia,lamellipodia,or directly with the plasma membrane,and the phagocytized bacteria can be digested by lysosomes.It was also found that the ultrastructure of the hae-mocytes did not damage after phagocytosis of E.coli and S.aureus while after phagocytosis of V.an-guillarum,the haemocytes ultrastructures were obviously damaged,and the apoptosis or death of the haemocytes occurred.We concluded that the difference of phagocytosis of R.philippinarum haemo-cytes to three kinds of bacteria was related to the size,aggregation degree and pathogenicity of the bac-teria.
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