Demonstration of immune complexes in spontaneous and histamine-induced lesions and in normal skin of patients with leukocytoclastic angitis.

Clinical and laboratory observations have strongly suggested that leukocytoclastic angitis is an immune complex disease. Since immune complexes can be visualized as electron-dense deposits by electron microscopy (EM), this method was used in conjunction with direct immunofluorescence (IF) to determine whether complexes could be demonstrated in spontaneous lesions, and in uninvolved skin in which the vessels were made permeable by the local injection of histamine. Histamine-induced wheals were produced in the uninvolved skin of patients with active angitis. In the resulting wheal, EM studies revealed electron-dense deposits characteristic of immune complexes in postcapillary venules and direct IF studies demonstrated complement and immunoglobulins in the vessel walls. Neutrophils in varying stages of disintegration were present thereby reproducing the histopathologic changes of spontaneous lesions. EM and IF studies of nonmanipulated uninvolved skin also revealed electron-dense deposits and immune reactants in the vessel walls. Neutrophils were not present, however. This observation indicates that immune complexes are deposited in vessels before tissue damage ensues. Study of spontaneous lesions older than 24 hr revealed only fibrin by EM and no immune reactants by direct IF. In spontaneous lesions less than 24 hr old, electron-dense deposits and fibrin were seen by EM, and complement and immunoglobulins by IF. Histamine-induced wheals should be a useful device to investigate patients with disorders that have an immune complex pathogenesis.