The influence of in vitro and in vivo exposure to antibiotics on mitogen-induced proliferation of lymphoid cells in rainbow trout (Oncorhynchus mykiss)

The influence of five different antimicrobial drugs on mitogen-induced lymp hoid cell proliferation in vitro and after oral administration of the drugs was studied in rainbow trout (Oncorhynchus mykiss). The drugs tested were: oxolinic acid, oxytetracycline, florfenicol and trimethoprim in combinatio n with sulfadiazine in ratio 1:5. In the in vitro tests, trimethoprim:sulfa diazine increased the H-3-thymidine incorporation into the DNA of phytohaem agglutinin and lipopolysaccharide-stimulated lymphoid cells while all the o ther drugs tested interfered negatively with the incorporation in a dose de pendent manner. In the experiment with oral drug administration, the fish w ere fed 10 days with a therapeutic dose of the drugs. After the drug treatm ent, lymphoid cells were isolated from the head kidney of the fish and test ed for proliferating capacity. All drugs except trimethoprim+sulfadiazine, suppressed the mitogenic response of the head kidney cells. The suppression of the response was more severe in phytohaemagglutinin-stimulated than in lipopolysaccharide-stimulated cells indicating that the T-cells were more v ulnerable to the toxic effects of the drugs than B-cells. (C) 2000 Academic Press.