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Haemocyte parameters associated with resistance to brown ring disease in Ruditapes spp. clams

Summary: Haemocyte parameters associated with resistance to brown ring
disease in Ruditapes spp. clams
Bassem Allam*, Kathryn A. Ashton-Alcox, Susan E. Ford
Haskin Shell®sh Research Laboratory, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349, USA
Received 28 August 2000; received in revised form 12 December 2000; accepted 18 December 2000
Brown ring disease (BRD) is a shell disease caused by Vibrio tapetis. This pathogen disturbs the periostracal lamina causing
the appearance of a brown conchiolin deposit on the inner face of the shell, within the extrapallial space. Although differences in
resistance to BRD have been documented, their relationship to possible defense functions has never been investigated. In this
study, ¯ow cytometry was used to analyze cellular parameters in asymptomatic and experimentally infected Ruditapes philip-
pinarum from France and the west coast of the USA. Parallel analyses were made on Ruditapes decussatus, the native European
clam, which is highly resistant to BRD. In the haemolymph and extrapallial ¯uid of animals without BRD, total haemocyte
counts, the percentage of granulocytes, and the phagocytic activity against latex beads or V. tapetis by the haemocytes were
signi®cantly higher in American R. philippinarum than in French R. philippinarum. In most cases, levels in R. decussatus were
the highest of all three groups. Four weeks following challenge with V. tapetis, BRD prevalence reached 52 in American clams
and 100% in French specimens, but only 37% in R. decussatus. In symptomatic animals, phagocytosis of V. tapetis increased
signi®cantly in the resistant species of clam, R. decussatus, was unchanged in US clams, and decreased signi®cantly in FR
specimens when compared to asymptomatic individuals from each population. Ingestion of V. tapetis by haemocytes in the
extrapallial ¯uid, which is in contact with the periostracal lamina, could be the main defense mechanism used to counter
the pathogen. Our results suggest that resistance to BRD may well be related to the concentration of granular haemocytes and


Source: Allam, Bassem - School of Marine and Atmospheric Sciences, SUNY at Stony Brook


Collections: Biology and Medicine; Environmental Sciences and Ecology