Enhancement of Perkinsus marinus disease progression in TBT-exposed oysters (Crassostrea virginica)

In vitro exposure of Crassostrea virginica hemocytes to tributyltin (TBT) can inhibit antimicrobial defense mechanisms dependent on reactive oxygen intermediates, as measured by chemiluminescence (CL). However, tissue TBT concentrations attained in this in vivo study (˜ 7500 ppb, dry weight) did not inhibit hemocyte recruitment, phagocytosis, CL activity or serum lysozyme. This TBT level was nevertheless effective in enhancing progression and lethality of Perkinsus marinus infections. Immune stimulation was found to be associated with advanced P. marinus infections, as indicated by increased hemocyte recruitment into the circulation and increased CL activity. This played no apparent role in controlling the infection and was insensitive to TBT. Using this battery of standard assays of defense-related functions, the exacerbation of P. marinus infections by TBT could not be attributed to its putative immunosuppresive activity.