Generation of Monoclonal Antibodies to the Rabbit Interleukin‐2 Receptor a Chain (CD25) and Its Distribution in HTLV‐1‐transformed Rabbit T Cells

Rabbits can be infected with human retroviruses such as human T‐cell leukemia virus‐1 (HTLV‐1) and human immunodeficiency virus (HIV), and provide useful animal models to study retroviral diseases such as adult T‐cell leukemia and HIV. Previously we have succeeded in generating monoclonal antibodies (mAbs) against rabbit CD4, CD5 and CD11a antigens. To make this animal species more amenable to cellular and molecular studies, we have attempted to extend the panel of mAbs against rabbit CD antigens. Here we report on the generation of three neutralizing mAbs against interleukin‐2 receptor α chain (IL‐2Rα) (CD25), Kei‐α1 (IgG2b), Kei‐α2 (IgG2a) and Kei‐α3 (IgG1). They specifically recognize the rabbit Mr 55,000 IL‐2 binding protein, IL‐2Rα, and completely inhibit both high‐ and low‐affinity IL‐2 binding to F648b cells that express IL‐2Rα as well as IL‐2Rβ. The use of mAb Kei‐α1 confirmed that the rabbit IL‐2Rα is not only a low‐affinity IL‐2R on its own but also an essential component of high‐affinity IL‐2R as found in other animal species, and that rabbit activated T cells including HTLV‐1‐transformed cell lines express high levels of the IL‐2Rα. Together with mAbs against various rabbit CD antigens that we reported previously, these neutralizing mAbs to IL‐2Rα will be valuable for studies of human retrovirus infections, such as those induced by HTLV‐1 or HIV, in rabbits.