The Streptokinase-plasminogen System: III. Histopathology of Enhanced Streptococcal Virulence in Rabbit Skin due to Activation of this System

We investigated the histopathology of enhanced streptococcal virulence associated with activation of the streptokinase-plasminogen (SK-PG) system by applying a battery of histochemical stains to paraffin sections of lesions in rabbit skin to illustrate the inflammatory response. Special emphasis was placed on demonstrating fibrin. Lesions from a previously described experimental model were examined at 1, 4, 10, 16, 24, 48 and 96 hours following injection of group A SK-positive streptococci. The histopathology of the lesions showing enhanced virulence was identical to that of the controls. No difference in fibrin or any other parameter of inflammation was found to explain the enhanced virulence. Because the course of the virulence was determined before 24 hours, we investigated the 4 and 20-hour periods in great detail with both SK-positive and SK-negative streptococci. The histopathology of these lesions was also similar. Our results suggest that the enhanced virulence is caused by reactions in the amorphous ground substance and may be due to the general proteolytic effect of plasmin rather than to lysis of fibrin.