The addition of plasminogen and streptokinase to rabbit serum results in appearance of chemotactic activity which is relatively heat-labile and dialyzable. Generation of this activity requires heat-labile factors in serum, but not the sixth component of complement. The optimal mole ratio for generation of chemotactic activity is 1:1 to 1:3 for plasminogen to streptokinase. Neither material alone is sufficient to generate the activity in fresh serum. Generation of chemotactic activity can be blocked by the presence of ϵ-aminocaproic acid. This plasmin-generated chemotactic factor sediments slowly in a sucrose density gradient during ultracentrifugation.

The addition of plasminogen and streptokinase to rabbit serum containing the preformed chemotactic factor (activated trimolecular complex of C'5, C'6, C'7) causes destruction of the chemotactic factor and loss of hemolytic activity of the sixth component of complement. The same mole ratio of reactants for optimal expression of the phenomenon holds as for plasmin generation of chemotactic activity in untreated serum.

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