The popliteal lymph node assay in 1996

Abstract The popliteal lymph node (PLN) assay is based on the assumption that a mechanism similar to a graft-versus-host (GvH) reaction is involved in ‘GvH-like’ drug-induced side-effects, including generalized lymphadenopathy, serum sickness-like disease, scleroderma-like reaction and the lupus syndrome. An increased PLN weight 7–10 days after injection of the test article into the footpad is generally held as a positive response. Most, if not all compounds reported to induce pseudo-GvH side-effects in man (namely positive model compounds) have been shown to induce positive PLN responses in mice and/or rats. Reproducible results have been obtained in several laboratories, in some instances blindly. However, positive responses have also been obtained with the negative model compounds acetone and imipramine. Flow cytometry analysis and conventional histology failed to help differentiate between a true GvH response and a primary irritative effect. In order to confirm the potential value of the PLN assay to predict the risk for drug-induced GvH-like reactions, mechanistic studies are urgently needed.