ABSTRACT
OBJECTIVE: To investigate the effects of copper exposure and recovery from copper toxicosis on the nonspecific immune response in Mycobacterium marinum-inoculated goldfish. ANIMALS: Goldfish (Carassius auratus) with a mean weight of 33.5 g. PROCEDURE: Superoxide (O2-) production was measured in fish 2 to 6 weeks after injection with phosphate-buffered saline (PBS) solution or M marinum (10(2) to 10(7) colony-forming units [CFU]/fish). Then, paired groups of fish were injected with PBS solution or 10(4) CFU of M marinum and exposed to copper (100 microg/L) for 7 days or for 4 days with 3 days of recovery. One paired group not exposed 14 days later to copper served as control fish. Phagocyte production of O2-was measured by use of the nitroblue tetrazolium reduction assay. Inflammation and bacterial colony counts were determined by use of routine histologic and microbiologic procedures. RESULTS: Superoxide production achieved a maximal response 2 to 4 weeks after M marinum inoculation. Compared with control fish, O2- production increased in the groups exposed to copper but then decreased in the exposed groups that were allowed to recover. Superoxide response and peritoneal inflammation were greater in M marinum-inoculated groups than in non-inoculated groups. CONCLUSIONS: Copper exposure and inoculation with M marinum increased O2- production, whereas recovery after exposure decreased O2- production, even in fish that were immunostimulated by M marinum. CLINICAL RELEVANCE: When the antimicrobial oxidative response is suppressed after copper exposure, steps should be taken to avoid imposing additional stress and minimize the possibility of resurgent or secondary pathogenic infections.