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.