LOCALIZATION OF CATHEPSIN-B AND CATHEPSIN-D IN THE SYNOVIAL LINING CELLS OF THE NORMAL RAT TEMPOROMANDIBULAR-JOINT BY IMMUNO-LIGHT AND IMMUNO-ELECTRON MICROSCOPY

The localization of cathepsins B and D in the synovial lining cells an d distribution of the lining cells containing these cathepsins in the normal rat temporomandibular joint (TMJ) were examined immunocytochemi cally in thick (8-10 mu m) and semithin (1 mu m) cryosections with the avidin-biotin-peroxidase complex method and in ultrathin sections wit h the gold-labeled IgG method. In the thick sections, strong immunorea ctivity for cathepsins B and D probably in the type A cells (not clear at this level), was observed simultaneously in the superficial layer of the synovial membrane. This reactivity was strong at the following portions of the synovial membrane located adjacent to the blood vessel s: I) at the anterior portion and 2) medial-posterior portion facing t he upper joint cavity, and 3) at the anterior portion and 4) lateral p ortion facing the lower joint cavity. In semithin cryosections, strong immunoreactivity for cathepsins B and D was simultaneously found in t he type A cells which have numerous pseudopodia and vacuoles, while we ak granular immunoreaction products for both cathepsins were also obse rved in the type B cells. In control sections, no type A or B cells sh owed immunoreactivity for these cathepsins. In the ultrathin sections, numerous gold particles indicating cathepsins B and D were detected i n the lysosomes and phagolysosomes of the type A cells facing the late ral intercellular spaces and joint cavity. In the phagolysosomes, thes e cathepsins were characteristically co-localized. On the other hand, in the type B cells, a few gold particles were localized only in the l ysosomes. Judging from these findings, it is suggested that type A cel ls predominantly contain cathepsins B and D, and that these cathepsins may be restricted within the cells (lysosomes) without extracellular release in the normal rat TMJ. It is also suggested that materials suc h as cell debris in the lateral intercellular spaces between the type A cells or in the joint cavity are endocytosed by phagosomes nearby, a nd are digested by proteolytic enzymes (cathepsins B and D) in the lys osomes. In addition, it is considered that this function in the type A cells is most conspicuous at the anterior portion of the synovial mem brane of the normal rat TMJ.