The contact system. Polyphosphates (P-P-P-P-P-P) bind FXII and promote its autoactivation to FXIIa. HK binds polyphosphates and promotes FXI activation by FXIIa, and the resultant FXIa then propagates coagulation leading to thrombin generation. FXIIa also activates HK-bound prekallikrein (PK) to kallikrein (K), which activates FXII in a reciprocal manner to promote additional FXIIa generation. Release of bradykinin from HK cleaved by K induces an inflammatory response.