Electron microscopy of porcine synovial membrane cell layer in Streptococcus equisimilis arthritis

Abstract The fine structure and cytochemistry of infected joints from Streptococcus equisimilis infected swine were studied. All infected synovial cells at three days after inoculation appeared similar. An extensively formed endoplasmic reticulum with a more prominent Golgi apparatus was evident. Between the endoplasmic membranes was a material of intermediate electron scattering ability. Vesicle formation or pinocytic vesicles were not observed. Prominent filopodia had formed with frequent blebbing of the cytoplasmic membrane. At 30 days after inoculation, all synovial cells appeared similar to the dedifferentiated tissue culture cell. They possessed large nuclei with little nucleoplasm and extensive, finely segmented endoplasmic reticulum with a clumping of ribonucleoprotein (RNP) particles of the endoplasmic membrane. Mitochondria were evident, but a Golgi apparatus was not prominent in any of the synovial cells. Acid phosphatase activity of the normal synovial cell was confined to vacuoles at the periphery and to discrete foci within the cytoplasm. At three days after inoculation there appeared to be a dispersion of the acid phosphatase particles within the cytoplasm of the synovial cells. A well developed rough endoplasmic reticulum was present in most infected synovial cells. Dedifferentiation of synovial cells and altered RNP endoplasmic reticulum relationship suggested altered protein synthesis by the synovial cells.