The presence of contaminants in aquatic environments may compromise th
e health and survival of fish. Many of these compounds are known immun
otoxins in mammals however, relatively little information is available
on the immunotoxic responses of fish to these pollutants. Organotins
are examples of widespread industrial and agricultural compounds which
persist in aquatic environments. In this study, we investigate the ef
fects of tributyltin (TBT) and its dealkylated metabolite dibutyltin (
DBT) on fish immune responses. Immune cells were isolated from the spl
een and head kidney of juvenile rainbow trout (Oncorhynchus mykiss,kis
s) and exposed to 0, 2.5, 50 and 500 ppb of either TBT or DBT. Mitogen
esis was quantified by tritiated thymidine incorporation into cells cu
ltured with the mitogens concanavalin A (Con A) or lipopolysaccharide
(LPS). No changes in immune function occurred at the lowest organotin
dose of 2.5 ppb. Con A-stimulated mitogenesis was significantly suppre
ssed by 85% in spleen cells on exposure to 50 ppb DBT. LPS-stimulated
mitogenesis was significantly suppressed by 96% in spleen cells and by
58% in head kidney cells with 50 ppb DBT. The highest concentration o
f 500 ppb of TBT and DBT inhibited both Con A-and LPS-stimulated mitog
enesis by more than 95% in both head kidney and spleen cells. Flow cyt
ometric analysis revealed dose-dependent changes in the cell populatio
n profile which correlated with the inhibition of mitogen-stimulated l
ymphoproliferation. In contrast, natural cytotoxic cell activity was n
ot inhibited by in vitro exposure to either compound, as determined by
the lysis of chromium-51-labelled K562 human erythroleukaemia cells a
nd P815 mouse mastocytoma cells. These results show that organotins ha
ve both functional and tissue-specific effects on the fish immune syst
em, i.e. spleen>head kidney tissue and, in general, LPS-responsive>Con
A-responsive leukocytes. In aquatic systems, TBT is considered to be
the most toxic organotin compound, and this toxicity decreases with pr
ogressive dealkylation to di- and mono-organotins. However, our result
s indicate that DBT is a more potent immunotoxin than TBT, and suggest
a need for the reassessment of the potential toxicity of DBT to aquat
ic organisms. (C) 1998 Elsevier Science B.V.