Applicability of the popliteal lymph node assay in the Brown-Norway rat

A number of drugs and chemicals can induce autoimmune disorders. Previous studies suggested the popliteal lymph node (PLN) assay might be a suitable and reliable model to detect such compounds in the mouse. The applicability of this assay has been examined in the Brown-Norway rat using a panel of positive as well as negative reference compounds. Popliteal lymph nodes were excised and weighed seven days after subcutaneous injection of 5 mg of each compound into one footpad. Interestingly, all negative reference compounds produced no significant increase in PLN weight index whereas four positive reference compounds were associated with PLN-weight indices greater than 2.3. However, no increase in PLN weight was noted in procainamide- and isoniazide-treated rats as previously reported in the mouse. This first set of experiments indicates that the PLN assay is applicable to Brown-Norway rats and warrants further investigation.