Classification and characterization of immune haemocytes in the larvae of the Indian fritillary, Papilio hyperbius (Lepidopetra: Nymphalidae)

Abstract

In this study, haemocytes present in Papilio hyperbius Linnaeus were identified and characterized. Six different types of haemocyte were recorded in the haemocoel of this species of insect: prohaemocytes, plasmatocytes, granulocytes, spherulocytes, adipohaemocytes and oenocytoids. Of these the granulocytes were found to be responsible for cell-mediated immune responses such as phagocytosis. Granulocytes that were exposed to immunity inducers (carboxylate-modified polystyrene latex beads [CLBs] and Escherichia coli) had fan-like or pod-like structures on their cell membranes. The lysosomes in granulocytes were activated 2 h after injection with E. coli and after 12 h, all granulocytes exhibited highly activated lysosomes. After 24 and 48 h, the lysosome activity in granulocytes decreased. Transmission electron microscopy revealed that phagocytosis, which was mediated by granulocytes in the early hours of the E. coli infection, led to the formation of one phagosome for one E. coli within the cytosol. Moreover, as time passed, endosomes or lysosomes of different size developed. Subsequently, the phagosomes and lysosomes fused and E. coli were eliminated. After this series of immune responses, the nuclei of the granulocytes were indistinct and their cellular activity decreased. Hence, as old immune cells were replaced by new ones, active and healthy immune haemocytes were presumed to be maintained in the hemocoel.