Interleukin-10 is an unequivocal Th2 parameter in the rat, whereas interleukin-4 is not.

Exposure of Wistar rats to the immunotoxic compounds hexachlorobenzene (HCB), bis(tri-n-butyltin)oxide, and benzo(a)pyrene was previously found to affect mRNA expression of interleukin (IL)-2, IL-2R alpha-chain, and interferon (IFN)-gamma, the prototypic Th1 cytokine. In contrast, the mRNA expression of IL-4, the prototypic Th2 cytokine, was unaffected. This latter finding suggested that the IL-4 mRNA expression may not be an unequivocal parameter for Th2 responses in the rat. In order to obtain such a parameter the present study was performed, consisting of two types of experiments. Expression and production of IL-4 as well as IL-10, a second Th2 cytokine, were measured. First, Lewis (Th1 prone) and Brown Norway (BN; Th2 prone) rats were exposed to HCB. Exposure was previously found to increase the serum immunoglobulin (Ig)E levels, an IL-4-dependent response, in BN but not Lewis rats, and in Lewis rats to aggravate experimental allergic encephalomyelitis (EAE), severity being inversely related to IL-10 levels. Secondly, BN rats were infected with Trichinella spiralis, an infection previously found to induce IL-4 production. HCB exposure did not affect IL-4 mRNA expression in either strain, while IL-4 production was decreased in Lewis and unaffected in BN rats. In Lewis rats both the mRNA expression and the production of IL-10 were decreased. The T. spiralis infection induced IL-4 and IL-10 mRNA expression, as well as IL-10 production. In contrast, the IL-4 production was strongly reduced. Thus, both the IL-10 mRNA expression and production correlated with the EAE development and T. spiralis infection. In HCB exposed Lewis rats and T. spiralis infected BN rats the IL-4 mRNA expression correlated with IgE levels and T. spiralis infection, respectively, whereas the IL-4 production lacked correlation in all cases. Collectively, these results suggest that IL-10 is an unequivocal Th2 parameter in the rat, whereas IL-4 is not.