Fine Structural Analysis of Rabbit Synovial Cells I. The Normal Synovium and Changes in Organ Culture

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Abstract
The distinction between fibroblast and macrophage‐like cells in the rabbit synovium is relatively easy to assess. A careful analysis of the two types of cells indicates that the Golgi apparatus, pinocytotic vesicles and lipid inclusions are more commonly observed in fibroblast‐like or F cells. The macrophage‐like or M cell is characterized by numerous short filopodia and cytoplasmic inclusions and vacuoles. Using these criteria a count of 700 lining cells revealed 63% fibroblasts, 34% macrophage‐like and 3% intermediate cells. In organ culture there is a gradual disappearance of macrophage‐like cells most marked between Day 1 and 3 due possibly to cell migration. The typical lining cell in culture has multiple lipid inclusions, widened endoplasmic reticulum and gray granular inclusions. Thus, the surviving synovial lining cell in organ cultures appears to be similar to the fibroblast of the original synovium.