Abstract
The frequency, age of onset and organ distribution of spontaneously occurring vasculitis was examined in a sequential study with 170 MRL mice of both substrains. Necrotizing vasculitis was seen in 55·8% of MRL/Mp-lpr/lpr mice studied, beginning at the age of 3 months. The kidney and urinary bladder were most frequently involved. In MRL/Mp-+/+ mice necrotizing vasculitis was much less frequently present (7·6%), beginning at the age of 18 months, and was seen only in the kidney, stomach and testes. In both substrains mononuclear infiltration of pulmonary vessel walls preceded the occurrence of necrotizing arteritis in other organs. The immunofluorescence study revealed the presence of immune complex components (immunoglobulin G, C3, murine leukaemia virus antigen gp71) in the vessel walls of the renal arteries of six out of 36 lpr/lpr mice with necrotizing arteritis.