Serologic characterization of Rocky Mountain spotted fever. Appearance of antibodies reactive with endothelial cells and phospholipids, and factors that alter protein C activation and prostacyclin secretion.

Rocky Mountain spotted fever (RMSF) takes its name from the characteristic rash that occurs as a consequence of vasculitis associated with rickettsial invasion of the endothelium. The authors examined sera from 14 patients with serologically confirmed RMSF for the presence of antibodies (IgG and IgM) reactive with human umbilical vein-derived endothelial cells and with the phospholipids cardiolipin (CL) and phosphatidyl serine (PS). Sera from 7 patients (50%) exhibited antiendothelial antibodies, and 10 (71%) patient sera reacted with CL and/or PS. Because such antibodies may interfere with or augment endothelial thrombosis-related activities, acute and convalescent sera were tested for their effects on endothelial PGI2 secretion and protein C activation. Acute sera from two patients and convalescent sera from four patients stimulated protein C activation. Additionally, sera from five acute and nine convalescent cases inhibited basal endothelial PGI2 secretion, but sera from two acute and three convalescent cases stimulated thrombin-dependent PGI2 secretion. These results demonstrated that, in a significant proportion of patients, RMSF was accompanied by the appearance of antibodies that bound to endothelial cells and to phospholipids; some of these antibodies may have altered anticoagulant endothelial functions.