A permeability factor released from leukocytes after phagocytosis of immune complexes and its possible role in the Arthus reaction

Abstract Evidence is presented that a substance is released from leukocytes when they ingest Ag-Ab precipitates, which causes an increase in vascular permeability when injected intradermally into normal rabbits. It is postulated that this substance is released when leukocyte granules (lysosomes) enter the phagocytic vacuoles containing the immune precipitates (phagosomes), thus giving rise to a digestive vacuole. Isolated Leukocyte granules incubated with immune complexes also increases vascular permeability. Release of the postulated substance probably operates in vivo in the Arthus reaction. The possible nature of this substance is briefly discussed.