Immune responses of phenoloxidase and superoxide dismutase in the manila clam Venerupis philippinarum challenged with Vibrio tapetis--part II: combined effect of temperature and two V. tapetis strains.
2015
Manila clams, Venerupis philippinarum (Adams and Reeve, 1850), were experimentally infected with two
different bacterial strains and challenged with two different temperatures. Bacterial strains used in this
study were Vibrio tapetis strain CECT4600T, the causative agent of Brown Ring Disease (BRD) and
V. tapetis strain LP2, supposed less virulent to V. philippinarum. V. tapetis is considered to proliferate at
low temperatures, i.e. under 21 °C. In a global warming context we could hypothesize a decrease of mass
mortalities caused by V. tapetis but these thermal changes could also directly impact the immune system
of the host V. philippinarum. Thus, the aim of this study was to investigate the effects of the extrapallial
injection with V. tapetis combined with temperature challenge on two enzymes activities in
V. philippinarum. More precisely, after infection, phenoloxidase (PO) and superoxide dismutase (SOD),
two major enzymes involved in immune response, were studied for 30 days in two compartments: the
mantle and the hemolymph. Conchyolin Deposit Stages (CDS) and Shell Repair Stages (SRS) were also
determined 30 days post-injection as a proxy of the virulence of the tested strains. In this study, we
highlighted that hostepathogen interaction in a varying environment affects the enzymatic response of
the host. The coupled effect of V. tapetis injection and temperature challenge was detected 30 days post
injection and resulted in virulence differences. These findings were supported by CDS and SRS determination
in clams and lead to the conclusion that clam's immunity could be enhanced at 22 °C while
V. tapetis virulence is lowered at this temperature. Another result of our study was the increase of PO and
SOD basal activities as clams are exposed to warmer temperature.
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