Abstract
The defense reactions against biological (Histoplasma capsulatum and Escherichia coli) and non-biological materials (China ink and nylon thread) were tested in vivo in third instar larvae of Dermatobia hominis. The cellular defense performed by larval hemocytes was observed under electron microscopy. China ink particles were phagocytosed by granular cells 5 h after injection. E. coli cells were internalized by granular cells as early as 5 min after injection and totally cleared 180 min post-injection, when many hemocytes appeared disintegrated and others in process of recovering. H. capsulatum yeasts provoked, 24 h after being injected, the beginning of nodule formation. Nylon thread was encapsulated 24 h after the introduction into the hemocoel. Our results suggest that granular cells were the phagocytic cells and also the responsible for the triggering of nodule and capsule formation. In the presence of yeasts cells and nylon thread, they released their granules that chemotactically attracted the plasmatocytes that on their turn, flattened to surround and isolate the foreign material.
Highlights
Insects are known to possess efficient defense mechanisms against foreign particles
We experimentally investigated the role of third larval instar hemocytes of Dermatobia hominis in response to different kind of foreign material, such as nylon thread implants, and injections of China ink, Escherichia coli and dead yeast Histoplasma capsulatum suspensions
Besides the intact and disrupted granular cells, spreaded plasmatocytes were clearly seen attached to the clot, characterizing the beginning of the encapsulation of the nylon thread (Fig. 7). Results of this investigation demonstrate that the immune system in Dermatobia hominis performs different responses depending on the type, size, and/or number of the foreign material
Summary
Insects are known to possess efficient defense mechanisms against foreign particles. Among these mechanisms are phagocytosis, nodule formation, encapsulation and hemolymph coagulation. The third instar larvae weight from 30 to 900 mg, when at the end of this instar they leave the host to pupate This parasitism is responsible for considerable loss in economy, as it causes decrease in milk production, damage in hide and livestock weight loss. The control of this parasitism has been made by using chemical agents and the impact they may produce in the environment and in the human health is not estimated. The knowledge of the physiology and the defense mechanisms of the parasite is one of the tools to reach this aim
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