Plasma kallikrein activation and inhibition during typhoid fever

As an ancillary part of a typhoid fever vaccine study, 10 healthy adult male volunteers (nonimmunized controls) were serially bled 6 days before to 30 days after ingesting 10⁵ Salmonella typhi organisms. Five persons developed typhoid fever 6-10 days after challenge, while five remained well. During the febrile illness, significant changes (P< 0.05) in the following hematological parameters were measured: a rise in α₁-antitrypsin antigen concentration and high molecular weight kininogen clotting activity; a progressive decrease of platelet count (to 60% of the predisease state), functional prekallikrein (55%) and kallikrein inhibitor (47%) with a nadir reached on day 5 of the fever and a subsequent overshoot during convalescence. Despite the drop in functional prekallikrein and kallikrein inhibitor, there was no change in factor XII clotting activity or antigenic concentrations of prekallikrein and the kallikrein inhibitors, Cl esterase inhibitor (Cl-INH) and α₂-macroglobulin. Plasma from febrile patients subjected to immunoelectrophoresis and crossed immunoelectrophoresis contained a new complex displaying antigenic characteristics of both prekallikrein and Cl-INH; the α₂-macroglobulin, antithrombin III, and α₁-antitrypsin immunoprecipitates were unchanged. Plasma drawn from infected-well subjects showed no significant change in these components of the kinin generating system. The finding of a reduction in functional prekallikrein and kallikrein inhibitor (Cl-INH) and the formation of a kallikrein Cl-INH complex is consistent with prekallikrein activation in typhoid fever. The correlation of these changes with the drop in platelet count suggests that a common mechanism may be responsible.