Functional assays are mandatory for a correct prediction of immunotoxic properties of compounds in vitro.

An increasing aim in safety assessment of chemicals and drugs is to reduce, refine and replace animal testing, especially in the context of the new system for the registration, evaluation and authorisation of chemicals (REACH). Regarding immunosuppression, most methods are based on mitogen stimulation assays. To our knowledge the in vitro antibody response (Mishell-Dutton culture) has never been considered as an alternative to the existing animal tests nor has its potential of correctly predicting different immunosuppressant compounds been analyzed. Therefore, we designed a study comprising seven immunosuppressant and four negative compounds and compared the results to data obtained from rat mitogen stimulation experiments (analysis of proliferation, TNFalpha and IFNgamma release). The in vitro antibody response showed a high sensitivity and specificity. It is a promising assay for the prediction of immunosuppressive properties of chemicals and drugs, whereas the results from rat spleen cell mitogen stimulation assays were rather poor in respect thereof. Mitogen stimulation assays are restricted to certain cell types and the chosen endpoints, while any compound-induced alteration is likely to be detected in a functional assay like the in vitro antibody response, when several immunocompetent cells have to cooperate to result in the humoral response analyzed.