An Immunocytochemical Study on the Differentiation of Synoviocytes in the Knee Joint of Mouse

Abstract

This study was designed to observe the differentiation of synoviocytes in the knee joint of mouse by immunocytochemical technique. The feti were collected on the 15th, 16th, 17th, 18th and 19th day of pregnancy, and the I-day-old and 5-day-old neonates were also collected. The knee joints were fixed in Bourn's solution and processed and finally embedded in paraplast by routine method. The serial sections were stained in H&E. In order to visualize the lysozyme and the Ia antigen in the cell, rabbit anti-lysozyme antibody and monoclonal IgG2a anti-mouse I-Ad were used in the double-bridge peroxidase anti-peroxidase technique. To observe the ultrastructure of the synoviocytes, the junctional complex, the basal lamina and the type of capillaries in the synovial membrane, some tissues were embedded in Epon 812 by the usual method. The joint cavities were formed separately in the posterior portion of the patella and between the femur and tibia in the Ifi-day-old fetus. These were united in the 18-dayold fetus. The synoviocytes, which showed a positive reaction to anti-lysozyme, first appeared in the 18-day-old fetus. These synoviocytes were abundant on the luminal side of the primordial infrapatellar fat pad in the 19-day-old fetus but were absent on the surface of the meniscus and cruciate ligaments. The Ia antigen-positive synoviocytes first appeared in the 5-day-old neonate. In the types of synovial membrane, the fibrous type first appeared in the 17-day-old fetus, the areolar type in the 18-day-old fetus, and the adipose type in the 5-day-old neonate. The synoviocytes did not have the basal lamina at any age. The desmosomal junctions were observed between the synoviocytes in the 8-week-old adult. The capillaries supplying blood in the synovial membrane were the fenestrated type with closing diaphragms, but the basal lamina was incomplete. On the basis of above findings, it is obvious that joint cavities are formed by the fusion of small ones during fetal growth. The lysozyme-positive synoviocytes, which compose the synovial membrane, appear before birth, but the expression of the Ia antigen shows up after birth.