The effects of a live in vivo pathogenic infection on aspects of the immunocompetence of the common shore crab, Carcinus maenas (L)

Individuals of the common shore crab, Carcinus maenas (L.), were inoculated in the laboratory with sub-lethal doses of the Gram negative bacterium Listonella (= Vibrio) anguillarum and the effects of this live infection on aspects of the immunocompetence of the crabs were monitored over a 7 day incubation period. Following Listonella inoculation, there was a significant decrease in the number of circulating haemocytes in the crabs which was maintained throughout the 7 day incubation. This decrease was combined with a significant increase in the ratio of granulocytes to hyalinocytes in the case of the experimental crabs. There was also a significant elevation in the concentration of haemolymph hydrogen peroxide 7 days after inoculation. In the first 24 h post inoculation there was evidence of a decrease in the cellular store of the, immunologically important, enzyme phenoloxidase. After 7 days incubation however, this pattern was reversed and enzyme levels were higher in the experimental animals than the control crabs. The data are explained in terms of a temporary reduction in the immunocompetence of the infected crabs, evidenced by the reduced haemocyte number. This transient compromise of the immune system was followed by a recovery which gave rise to an elevated hydrogen peroxide concentration and phenoloxidase enzyme activity