EFFECTS OF SEX HORMONES ON BURSA OF FABRICIUS,WITH SPECIAL REFERENCE TO BURSIN-mRNA and B CELL APOPTOSIS.

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Structural changes in the bursa of Fabricius of white Leghorns after the intraperitoneal injection with high dose (100mg/kg) of androgen, estrogen and cortisone were examined. A large number of reticular epithelial cell (REC) -like structures that contained apoptotic B cells were observed. The majority of apoptotic B cell-containing REC-like structures had an epithelial nature and were mainly located in the corticomedullary region and, in part, in medulla. Most B cells seemed to undergo apoptosis synchronously in every REC-like structure, but one or two fully intact mature B cells were found in every one. By 5 days after steroid treatment, many vacuoles that contained apoptotic cells in various stages of degeneration were observed within the epithelium. We herein demonstrated that epithelium of REC-like structure had a weak phagocytic activity in the digestion of apoptotic B cells by the presence of phagolysosomes. Futhermore, we found that steroid treatment caused a progressive loss of the number of bursin-mRNA positive REC-like cells. The above results clearly indicate that steroids can induce B cell apoptosis through these hormone directly modulate RECs to produce the bursopoietic hormone, such as bursin.