Morphological changes of Carcinoscorpius rotundicauda amoebocyte and Escherichia coli during their interaction

Interaction between Carcinoscorpius rotundicauda amoebocytes and Escherichia coli or Staphylococcus aureus has shown that whilst E. coli was observed to lyse, S. aureus remained intact. The heavily granulated amoebocytes were activated by the lipopolysaccharide of E. coli to undergo dramatic morphological changes with time, leading to degranulation which caused lysis of the E. coli. Degranulation of the amoebocytes involved maturation of the larger electron dense granules (0.7-2.0 micron) which were apparently mobilised towards the cell membrane whilst undergoing a loss in electron density. Some of these larger granules were expelled at 15-30 min while other intracellular granules underwent further degranulation, where parallel filaments appearing like microtubules were evident, giving the granules a striated and less dense form. By 60 min, there was complete depolymerisation of the microtubular filaments giving rise to undefined, fused and homogeneously packed striations and particulate material in the cytoplasm; the smaller electron dense granules (0.3-0.7 micron) remained unchanged. This asynchronous degranulation and preferential expulsion of granules from only some amoebocytes while maintaining others intact, implies that the horseshoe crab has safeguards in its defence mechanism, hence ensuring its continued survival as a 'living fossil'.