Figure 5.

HE stained histological images of adipose synovium from (A) a knee joint of a normal rabbit, (B) 8 days postinoculation with S. aureus, and (C) 18 days postinoculation with LPS from E. coli. (A) In the cross section of normal adipose synovium, the intima (a) is seen as a densely populated cellular region that is one to three cells thick, while the subintima (b) is composed primarily of adipocytes (c) and small numbers of capillaries (d), small venules (e), and arterioles set in a randomly distributed matrix of loosely packed thin collagen fibrils (f). The sharp transition between the intima and subintima and the characteristic morphological details of each layer are easily observed. The cross section of adipose synovium from the S. aureus infected knee (B) demonstrates that a denuded intimal layer (g) and the adipocytes (c) of the thickened and edematous subintima have been largely replaced by an inflammatory cell infiltrate (h) consisting primarily of heterophils. Capillaries (i) are congested and their walls are thickened. Fibroblasts (j) are beginning to produce a delicate fibrillar matrix, while the meshwork of pre-existing collagen fibers is randomly displaced. The image of the inflammatory reaction that is present in the adipose synovium of the rabbit knee joint following LPS inoculation (C) demonstrates thickening of the intimal layer (a), and the normal population of subintimal adipocytes has been replaced by an inflammatory cell infiltrate (l) consisting primarily of lymphocytes relatively evenly distributed, along with fibroblasts in a collagenous matrix containing congested capillaries (i), arterioles (k), and venules (e). In some areas, edema (m) separates the matrix of collagen fibrils. Scale bars are 50 μm.