The correlation between morphological and biochemical changes produced by the antigen-antibody reaction was studied in cultures of tissue monocytes taken from sensitized animals. The cells were grown under conditions which allowed collection of samples from the culture fluid as well as microscopic observation.
Introduction of the antigen into the culture medium causes rapid release of a protease characterized by its susceptibility to sulfhydryl block and its optimum pH in the neutral range. Protease activation occurs simultaneously with morphological changes in the cytoplasm of the cultured cells. Delayed changes affecting the mitochondria and Golgi bodies appear after the peak of the proteolytic reaction and may be secondary to it. The gradual inactivation of the protease observed in the course of the antigen-antibody reaction will be discussed in a separate paper.