DAO 40:85-92 (2000)

The haemocytic origin of lymphoid organ spheroid cells in the penaeid prawn Penaeus monodon

Margaretha S. Anggraeni, Leigh Owens*     leigh.owens@jcu.edu.au

Department of Microbiology and Immunology, James Cook University 4811, Australia.
ABSTRACT: Studies on lymphoid organ spheroid (LOS) cells of Penaeus monodon were undertaken. Phenoloxidase and peroxidase assays showed that LOS cells have characteristics similar to semi-granular and, in particular, large granular haemocytes. The mean percentage of LOS cells positive for phenoloxidase and peroxidase was 85 ± 23 and 82 ± 23%, respectively. There was no significant difference between the sites of phenoloxidase and peroxidase activity in LOS cells (t = 1.617, df = 29, p > 0.05). The relative sectional area occupied by LOS cells relative to that of the stromal matrix cells from both laboratory-held and farmed prawns was not correlated to increasing weight or total length of the prawns (p > 0.05). An apoptosis detection assay showed that LOS cells were often apoptotic whilst stromal matrix cells were not. There was a significant difference (t = -5.533, df = 58, p < 0.05) in the mean percentage of apoptotic spheroid cells between laboratory-held prawns (52 ± 24%) and farmed prawns with midcrop mortality syndrome (MCMS) (80 ± 12%). In conclusion, LOS cells have the characteristics of exocytosed, granular haemocytes that have phagocytosed foreign material, particularly viruses, and probably constitute a major mechanism for penaeid antiviral defense.

Published in DAO Vol. 42, No. 2 (2000)

Quasi-immune response of Penaeus japonicus to penaeid rod-shaped DNA virus (PRDV)

C. A. Venegas^1,*, L. Nonaka¹, K. Mushiake², T. Nishizawa¹, K. Muroga^1,**

¹Laboratory of Fish Pathology, Faculty of Applied Biological Science, Hiroshima University, Higashihiroshima 739-8528, Japan
²Kamiura Station of Japan Sea-Farming Association, Kamiura, Oita 879-2602, Japan

*Present address: Unit of Aquatic Animal Pathology, Dept. of Animal Pathology, Faculty of Veterinary Sciences, University of Chile, Santiago de Chile, Chile.

E-mail: fpath@hiroshima-u.ac.jp
ABSTRACT: A quasi-immune response was demonstrated in kuruma prawn Penaeus japonicus infected naturally or experimentally with PRDV (penaeid rod-shaped DNA virus, also called white spot syndrome virus or WSSV), the causative agent of PAV (penaeid acute viremia). In the first step of this study, natural survivors 4 mo after a PAV outbreak demonstrated 94% relative percent survival (RPS) upon experimental PRDV challenge. Mortalities after challenge were confirmed by PRDV detection to be due to PAV using a PCR method. In the second step, experimental PAV survivors were produced by intramuscular (IM) injection of PRDV into naive shrimp subsequently reared collectively in a tank (A group) or individually in chamber units (B group). Survival was 41 and 90% in the A and B groups, respectively. A subsequent IM re-challenge of these PRDV survivor groups with PRDV made 32 d after the first challenge revealed a protective response with high RPS of 77 and 64%, respectively. These high survival rates suggested that PAV survivors (natural or experimental) were able to resist PRDV infection and that the resistance was not due to selection of naturally resistant shrimp during a PAV outbreak, but due to enhancement of an immune-like system (quasi-immune response) after exposure to PRDV. No PRDV neutralizing activity was revealed in the serum of the 4 mo natural survivors of the PRDV outbreak. However, it was found in their serum 17 d after they had been experimentally challenged with PRDV.