Clearance of bacteria injected into the hemolymph of the ridgeback prawn, Sicyonia ingentis (Crustacea: Decapoda): Role of hematopoietic tissue.

In an earlier investigation, radiolabelled bacteria injected into the hemolymph of the shrimp Sicyonia ingentis were cleared rapidly from circulation. Most of the bacteria were localized in the gills, followed by other organs including the heart, abdominal musculature, and hematopoietic nodules (HPN). We determined the organ-specific effectiveness of bacterial clearance and found the HPN to be the most effective on a per gram basis. Light and electron microscopy were used to determine the mechanism of clearance in the HPN. The HPN are readily permeable to individual bacteria, which then are recognized and phagocytosed exclusively by small granule hemocytes. Within the first hour, the bacteria are degraded, leaving only whorls of membrane in the phagocytic vacuoles. Subsequently, the hemocytes that ingested bacteria lyse, as has been observed in vitro. These observations support earlier suggestions that hemocytes in the HPN are functionally mature and held in reserve until they are released into circulation. © 1996 Wiley-Liss, Inc.

Organization of hematopoietic tissue in the intermolt lobster, Homarus americanus.

Hematopoiesis in the American lobster Homarus americanus, as in most decapod crustaceans, occurs in a thin tissue covering the dorsal surface of the foregut. This tissue is composed of loosely attached, ovoid lobules containing the hematopoietic precursors and maturing hemocytes. Release of hemocytes into the dorsal hemocoel is accomplished by rupture of a portion of the connective tissue capsule covering the lobule. Cross sections of the lobules contain between 6 and 40 hematopoietic cells, of which approximately 90% constitute stages in granulocyte maturation and 10% are intermediates in hyaline cell maturation. Hematopoietic precursors in these two lines are similar to those recently described in a penaeid shrimp Sicyonia ingentis. The mitotic rate averaged 5.1% (range = 0.7% to 15.8%) in intermolt lobsters, 90% comprised granulocyte precursors. © 1993 Wiley-Liss, Inc.

Morphological comparison of major arteries in the ridgeback prawn, Sicyonia ingentis.

The structure of the major vessels conducting hemolymph away from the heart of the ridgeback prawn, Sicyonia ingentis, was examined using light and electron microscopy. Three varieties of vessel wall morphology were observed. In most vessels the wall is composed of the following four layers, proceeding from lumen to exterior: (1) thick basal lamina, which selectively stains with Verhoffapos;s Van Giesonapos;s stain for elastin, (2) a continuous layer of cells rich in microtubules, (3) a loose connective tissue layer with highly branched cells widely separated by a fibrillar matrix, which also stains for elastin, and (4) a thin basal lamina covering the outer surface of the vessel. The dorsal abdominal artery shows the second type of vessel wall construction and differs from the previous vessels in the following ways: (1) the inner basal lamina is thinner, (2) a layer of striated muscle replaces the unspecialized endothelial layer, and (3) the connective tissue layer includes two well-organized bands of elastin-like material. The hematopoietic vessels that branch off the ophthalmic arteries display the third type of vessel wall morphology. The lumen of the vessel is lined by a very thin basal lamina, which completely encircles the endothelial cells. The rest of the wall is composed of hemocytes, presumably in various stages of maturation, embedded in a matrix of fibroblast-like cells and collagen fibrils. The morphology of the vessel wall is the same as that previously described for the tubules of the hematopoietic nodules. The functional significance of these different vessel walls is discussed.

CYTOCHEMICAL FEATURES OF SHRIMP HEMOCYTES.

Morphological studies suggest that there are several types of decapod hemocytes; however, distinguishing criteria based on conventional staining techniques are often subtle or ambiguous. Cytochemical features of ridgeback prawn (Penaeidae: Sicyonia ingentis) hemocytes were studied using specific stains for lysosomes, cytoplasmic contents, and granule enzymes. This approach facilitates the differentiation of cell types in the ridgeback prawn and provides information on the functions of and relation ships among different cell types. Agranular hemocytes and a subgroup of small granule hemocytes contain extensive cytoplasmic glycoprotein deposits which display smudgy, intense staining with Sudan black B. As previously shown, coagulogen-the clotting material in decapods-stains with Sudan black B when extracted from lysed hemocytes. Other hemocyte types display light staining limited to granule membranes. Lysosomes are not observed in agranular cells and are rarely present in small granule hemocytes with glycoprotein deposits. Small granule hemocytes without deposits and large granule hemocytes contain numerous lysosomes as shown by the presence of acid phosphatase, ß-glucuronidase, and nonspecific esterase. Acid phosphatase is observed in the Golgi body of these cells, within small vesicles, and in small granules. The granules in large granule hemocytes rarely show acid phosphatase reaction, yet small acid phosphatase-positive vesicles fuse with the large granules. The acid phosphatase in the large granules may exist in an inactive form. Prophenoloxidase activity is localized only in large granules. The physiological significance of hemocyte cytochemistry is also discussed.

Structure of hematopoietic nodules in the ridgeback prawn, Sicyonia ingentis: Light and electron microscopic observations.

The architecture and fine structure of the epigastric hematopoietic nodules of the ridgeback prawn, Sicyonia ingentis, are described. The nodules consist of a highly branched series of tubules that contain the maturing hemocytes within a connective tissue stroma. Hemocytes can exit the hematopoietic nodules by penetrating through fenestrations in the endothelial cell layer into the central hemal space or by migrating through the outer later of capsular cells and associated collagen fibrils. Four hemocyte categories were observed: agranular, small granule with cytoplasmic deposits, small granule without cytoplasmic deposits, and large granule hemocytes. This classification was based upon the presence, size, and type of cytoplasmic granules and the presence of cytoplasmic deposits. Only agranular cells and small granule hemocytes without cytoplasmic deposits appeared capable of division. Intermediate stages were observed between agranular hemocytes and small granule hemocytes with deposits and between small granule hemocytes without deposits and large granule hemocytes, suggesting existence of two distinct hemocyte lines.