Future research on wild cetaceans and, more in general, on free-living aquatic mammals should be aimed at evaluating the effect of environmental pollutants on host-pathogen interaction dynamics, thereby assessing whether contaminant-induced immunotoxicity could be related to a CD4+ T helper cells and/or to a CD8+ cytotoxic T cell reduction, together with a decreased splenic humoral immune response, as it happens in laboratory rodents exposed to lipophilic environmental contaminants (11). This evidence concerns the gene CD4 and immune system toxicity.