Evaluation of a model for post‐partum arthritis and the role of oestrogen in prevention of MRL‐lpr associated rheumatic conditions

SUMMARY Sixty‐eight percent of female MRL‐lpr‐ mice developed a post‐partum exacerbation of their mild spontaneous arthritis within 30 days of parturition‐ The flare became evident between 5 and 15 days after delivery. Histologically it was characterized by a significant increase of subsynovial inflammation and synovial hyperplasia without changes in the level of cartilage and bone erosion. Immunohistologically, marked subsynovial and frequent synovial staining of MHC class II bearing cells was noted, along with the sporadic presence of CD3, CD4, and CD43 receptor‐bearing cells in the subsynovium. Injection of physiological levels (0·08mg/kg) of estradiol on days 2, 3, 9, 15 and 20 post‐partum delayed and reduced the flare to 23% of the animals. Administration of pharmacological amounts (0·4mg/kg per day for 2 weeks following Freund's complete adjuvant injection) prevented adjuvant‐enhanced arthritis, reducing the incidence from 67% to the baseline 21% level‐ Deleterious changes in the underlying systemic lupus erythematosus (SLE), as demonstrated by proteinurea and mortality rate increases, were elicited only by the employed pharmacological amounts of estradiol. These results indicate that the MRL‐lpr mice might serve as a model for post‐partum flare of arthritis in SLE and rheumatoid arthritis by providing an approach to study the complexity of the effects of pregnancy on autoimmune diseases, and to obtain further evidence for the involvement of oestrogen in arthritis.