The intent of this study was to visualize changes in the density and location of
fibrinogen-related antigen (FRA) depositions within the murine vitreous space during the formation of a chronic mycobacterial-induced
uveitis (CMIU)
granuloma. Concurrent changes in cellular morphology of the
granuloma were also examined.
Fibrinogen derivatives within the exudates of granulomatous cell-mediated
inflammations may induce physical induration and numerous other phlogistic effects. However, technical limitations of conventional FRA staining methods have tended to underestimate the extent of their presence within this category of inflammatory lesions. Conventional H and E sections of the CMIU
granuloma confirmed the classic progression-early PMN influx, monocyte maturation and final macrophage and epithelioid cell dominance-described for such lesions.
Avidin-
biotin-complex staining utilizing a polyclonal mouse antifibrinogen then revealed a progressive increase in amorphous extracellular
fibrinogen-FRA-positive staining material as the
granuloma evolved. Thus, on day one the PMN influx showed no evidence of
fibrinogen-FRA staining; at one week heavy staining was evident in the anterior chamber and in consolidated (i.e. macrophage) regions of the
granuloma; at one month a heavy uniform staining appeared throughout the indurated
granuloma where macrophages and epithelioid cells predominated. Patterns of heavy deposition on macrophage surfaces were suggested. The likelihood that bulky accumulations of FRA in mature
granulomas are not solely
fibrin, and may account for granulomatous induration and persistence, is discussed.