Plasma thymulin concentrations, the thymus and organochlorine contaminant levels in seals infected with phocine distemper virus.

Blood samples collected from live common seals (Phoca vitulina) and grey seals (Halichoerus grypus) around the coast of Scotland and Northern Ireland during, and immediately after, an epizootic caused by phocid distemper virus (PDV) were analysed for thymulin content. Thymulin levels were compared with neutralization titres and concentrations of organochlorine contaminants (DDT and its metabolites, seven chlorinated biphenyl congeners) derived from blood and blubber samples collected from the same animals and analysed independently. Thymulin levels in grey seals (mean 2827 +/- 1355 fg/ml) were negatively correlated with the logarithm of virus neutralization titre. In common seals they varied significantly between age classes. There was no direct relationship between thymulin levels and contaminant levels in either species. However, when an estimate of time since exposure was included in the regression analysis for common seals, there was a highly significant relationship between thymulin and the two chlorinated biphenyl congeners with the highest concentrations in blubber.