Pathways of kinin formation and role in allergic diseases

We have developed new assays for the assessment of the plasma kinin forming system which have increased sensitivity and specificity. We utilize double-antibody ELISA assays for quantitation of complexes of activated Hageman factor-C1 inhibitor, kallikrein-C1 inhibitor, and kallikrein-alpha 2-macroglobulin which reflect activation of each enzyme. The fraction of cleaved high-molecular-weight kininogen is determined by immunoblotting using a monoclonal antibody to the light chain, and bradykinin is determined by radioimmunoassay. Activation of the Hageman factor-dependent pathway of kinin formation can occur when plasma is in contact with initiating surfaces or when C1 inhibitor function is diminished. The latter mechanism can occur in hereditary angioedema, in which the protein is absent or dysfunctional, or when plasma is diluted so that the effect of inhibitors is diminished and Hageman factor autoactivation is facilitated. Thus apparent "spontaneous" generation of bradykinin is seen upon incubation of plasma of hereditary angioedema patients under conditions in which normal plasma is unaffected. Studies of late-phase reactions have used a cutaneous model in which induced blisters are unroofed and challenged with antigen or buffer control using chambers which can be changed hourly. A time course of mediator release is obtained by assay of the blister fluids. Whereas most histamine is released during the first half hour, significantly elevated levels of activated Hageman factor and kallikrein complexes with C1 inactivator are seen in antigen-challenged sites between 4 and 6 hr. The presence of such complexes correlated with the presence of late-phase reactions rather than the histamine values or the magnitude of the immediate reaction. Although late-phase reactions are characterized by cellular infiltration, release of a variety of inflammatory low-molecular-weight mediators, and deposition of fibrin, activation of the Hageman factor-dependent pathway of kinin formation is also likely to be contributory.