[Ultrastructural and cytochemical study of the prothoracic gland of the silkworm of the fourth and fifth larval stages. I. Tunica propria and its relation to the connective tissue fibers and hemocytes]

Presence of sialic acid in prothoracic glands of Galleria mellonella (Lepidoptera)

The presence of sialic acid (SA) in prothoracic glands (PGs) of Galleria mellonella was determined by the methods of electron microscopy (EM), histochemistry, spectrophotometry (SP) and electronic ionization (EI)-mass spectroscopy. Histochemical observations were carried out by the cationic dye ruthenium red (RR), staining with and without neuraminidase digestion in the larval stage. Neuraminidase-sensitive SA was demonstrated by the decrease in the amount of RR-binding following neuraminidase digestion. The total amount of SA was found to be 0.09016 mg g(-1) in dry tissue by spectrophotometric determination. EI-mass spectroscopy results confirmed the EM and SP observations. The fragmentation scheme derived from EI-mass analysis exhibited the presence of the lactonized form of Neu5Gc7, 9Ac(2). On the basis of the various pieces of evidence described above, it was firmly concluded that Neu5Gc7, 9Ac(2) molecules were present in PGs of G. mellonella.

Functional amyloids in insect immune response

The innate immune system of insects consists of humoural and cellular responses that provide protection against invading pathogens and parasites. Defence reactions against these latter include encapsulation by immune cells and targeted melanin deposition, which is usually restricted to the surface of the foreign invader, to prevent systemic damage. Here we show that a protein produced by haemocytes of Heliothis virescens (Lepidoptera, Noctuidae) larvae, belonging to XendoU family, generates amyloid fibrils, which accumulate in large cisternae of the rough endoplasmic reticulum and are released upon immune challenge, to form a layer coating non-self objects entering the haemocoel. This amyloid layer acts as a molecular scaffold that promotes localised melanin synthesis and the adhesion of immune cells around the non-self intruder during encapsulation response. Our results demonstrate a new functional role for these protein aggregates that are commonly associated with severe human diseases. We predict that insects will offer new powerful experimental systems for studying inducible amyloidogenesis, which will likely provide fresh perspectives for its prevention.

Responses of hemocytes and gill tissues to sublethal cadmium chloride poisoning in the crab Paratelphusa hydrodromous (Herbst)

The hemocytic and gill tissue responses of the crab Paratelphusa hydrodromous (Herbst) to a wide range of sublethal concentrations of cadmium chloride (0.02-0.50 microM/L) were examined after a 30-day exposure using hemocyte counts (THC and DHC) and lamellar pathology. A continued reduction in the hemocyte counts and selective changes in the numbers of hyalinocytes and eosinophilic granulocytes was evident in the toxified crabs. Under sublethal stress, the hyalinocytes developed eccentric nuclei, granular cytoplasm and membrane blebs. Atypical shape, lobate nucleus, dense cytoplasmic deposits and granuloplasmic vacuoles were frequently observed in the granulocytes. Greater proliferation of prohemocytes and abnormal hemocyte morphology indicated cadmium-induced neoplastic transformation of hemocytopoietic organs. No major structural changes in the gills were noted at 0.02 microM CdCl2. Nodular gill disease (NGD), hemocytic hyperplasia and sloughing of walled off hemocytes were prominent lesions after 0.50 microM cadmium chloride exposure.

Hemocytes and hemocytopoiesis in Silkworms

A brief review is presented of the current state of ultrastructure, cytochemistry, and physiology of the hemocytes and meso- and metathoracic peri-imaginal-wing organs in silkworms. According to the accepted morphological classification, five circulating types of hemocytes are recognized in Bombyx mori as well as in Antheraea pernyi. They are prophemocytes or stem cells, plasmatocytes or pre-differentiated cells and three specialized cells, granulocytes, spherule cells and oenocytoids. During post-embryonic development the last four types are the most common in the circulating hemolymph. Plasmatocytes are considered to be pluripotent cells from which granulocytes, spherule cells and oenocytoids are derived. Contrary to the situation in most insects the plasmatocytes are not phagocytic in Antheraea. The granulocytes are efficient phagocytes. Both plasmatocytes and granulocytes are involved in pinocytosis. Another possible function of the granulocytes is hemolymph coagulation. The function of the spherule cells which contain a paracrystalline material (muco- or glycoproteins) is by no means clear. The phenoloxidase activity found within the cytosol of oenocytoids appears effective against the natural monophenol and diphenol substrates. The involvement of oenocytoids in the complex metabolism of phenols and particularly in the production of plasma phenolases has been reported. The mitotic division of five circulating hemocyte types is well known and was long regarded as the only mechanism of postembryonic hemocyte production. We present for silkworms, experimental evidence of the hemocytopoietic function of the meso- and metathoracic organs surrounding the imaginal wing discs. Ablation experiments demonstrate that the mitotic activity of free hemocytes is unable to maintain the normal hemocytogram in the absence of the two paris of organs. These organs are typically divided into cell islets ensheathed by a connective tissue membrane. Two types of islets may be classified by the disposition of the cells : the compact islets or aggregations of stem cells and the reticulate islets which are mainly composed of hemocytes at different steps of differentiation. The relative number of prohemocytes in the total hemocyte population ranges from 84 to 97 p. cent in organs of Antheraea pernyi. This well-defined cell type appears to be the major hemocyte type in hemocytopoietic organs. In Antheraea, the mitotic index (the relative number of mitotic hemocytes in the total cell population) varies from 0.5 to about 3 p. cent. Finally, our data direct attention to cyclic functional changes such as mitotic divisions and hemocyte differentiation which run parallel to the molting cycle.

[Cytochemical observations of hemocytes in decapod brachyuran crustacea (author's transl)]

Hemocytes from two species of crabs, Eriocheir sinensis and Carcinus maenas, have been submitted to different cytochemical reactions in order to bring out the nature of granules' content, either by specific coloration or be enzymatic digestion. Light as well as electron microscopy has been used. The granules appeared to be made essentially of basic proteins, rich in arginin and disulfide bridges but poor in tyrosin. These proteins are linked with nonglycogenic carbohydrates. Glycogen deposits of varied size are restricted to the cytoplasm in all the different cell-types but have never been detected inside the granules themselves. Lipids are poorly represented. The bulk of the granule material is made of neutral mucopolysaccharides although minute amounts of acid mucosubstances could be found in some instances.

Coagulocyte alterations in clotting hemolymph of Carausius morosus L

1. The structural changes in the coagulocytes of Carausius morosus during hemolymph coagulation in vitro have been studied under the PCM and in the TEM. 2. In agreement with former PCM observations on Carausius morosus, the coagulocytes are the only hemocytes to induce coagulation of the plasma. Immediately or after a few seconds upon withdrawal of the hemolymph, their structural changes consist of a considerable enlargement of the perinuclear cysterna and of direct ejection into the plasma of nuclear and cytoplasmic substances through microruptures of the cytoplasmic membrane. The other categories of hemocytes do not contribute to the plasma coagulation. Their structural alterations take place without breakage of the cytoplasmic membrane when the plasma reactions are already established. 4. These plasma reactions appear in the form of circular islands of granular material around the coagulocytes, of extension of the coagulum in the channels between the islands and of transformation of the clot into a network of threads. 5. As reported in other studies in the TEM, no specific organelle characteristic of the coagulocyte ultrastructure could be found in the coagulocytes of Carausius. 6. Owing to the absence of any specific structural criterion of identification, the results suggest that the functional difference between coagulocytes and the other categories of hemocytes as regards coagulation of the plasma might be caused in part by differences of permeability of the cell membranes.

Histochemical observations of the haemocytes of Locusta migratoria

Five of the six categories of haemocytes of Locusta migratoria, that is, the plasmatocytes, spherule cells, granulocytes, coagulocytes and oenocytoids, contain conspicuous granules of mucosubstance in their cytoplasm. The mucosubstance has been characterized by using a series of histochemical tests, including Alcian Blue staining at different pH levels and salt concentrations, the periodic acid-Schiff (PAS) test, the high iron diamine test, enzymatic digestions and sequential staining methods. The results indicate that four different mucosubstances occur in a granular form, although not all four are found in every blood cell type. The mucosubstances are a neutral glycoprotein and neuraminidase-resistant, sulphated and non-sulphated sialomucins. The non-sulphated sialomucin occurs in both periodate-reactive and -unreactive forms.