The observation of immune complex formation and deposition in the eyes of living rabbits.

Fluorescence microscopy of the conjunctival and episcleral circulations of the rabbit's eye has revealed for the first time the formation and deposition of intravascular and perivascular immune complexes in undisturbed capillaries in vivo. During intravascular immune complex formation, immune aggregates appear abruptly, at a critical antigen/antibody ratio, and embolize to the arterial side of the capillary bed. This is accompanied by a fall in the circulating platelet count. The emboli disperse over the ensuing 120 min. In frozen sections immune aggregates are coarsely granular and intraluminal at the moment they embolize. However, after they disperse, subendothelial granules of antigen can be found. IgG and C3 are associated with both intraluminal and subendothelial antigen. Perivascular immune complex formation is accompanied by an intense inflammatory response, which is absent after the deposition of an intravascular immune precipitate. The mechanism by which immune complexes may accomplish their transition across the capillary endothelium is discussed.