Increases in protein phosphatase 2B activity in lymphoid tissues and T-lymphocytes of autoimmune MRL/MpJ-lpr/lpr mice

The assay conditions for protein phosphatase 2B (PP2B) in crude extracts from mouse lymphoid tissues and lymphocytes were extensively investigated. Under the conditions elucidated, the PP2B activity was measured in autoimmune-prone MRL/MpJ-lpr/lpr mice (MRL/lpr mice) and two control strains, MRL/MpJ- +/+ mice (MRL/+/+ mice) and C3H/HeJ mice. In the control mice, PP2B activity was distinctly higher in spleen and thymus than brain and liver. PP2B activity was further elevated in spleen of MRL/lpr mice than in the controls. Furthermore, we observed a specific increase in PP2B activity in T lymphocytes from MRL/lpr mice as compared with in those from control mice. On the other hand, no alteration was observed in PP2B activity in B lymphocytes. These results suggest the involvement of PP2B in the abnormal signal transduction and proliferation of T lymphocytes in MRL/lpr mice.