Two major unresolved problems in
drug-related immune
agranulocytosis are understanding the mechanism by which sensitization takes place in vivo, and verification of the diagnosis. Using a sensitive, competitive
enzyme-linked immunoassay (ELISA) we were able to characterize the causative
antibodies in 13 patients with
drug-related
agranulocytosis [
metamizole (n = 5),
penicillin (n = 5),
dimethylaminophenazone (n = 1),
propyphenazone (n = 1) and
diclofenac (n = 1)]. Irrespective of the causative
drug, the majority of patients appear to have developed
autoantibodies (aab) in addition to
drug-dependent
antibodies (
ddab) of the
IgG and/or
IgM classes. In all cases related to
metamizole, and in the single case related to
diclofenac, the
ddab appeared to recognize only metabolites of the
drug since they were reactive in the presence of ex vivo
antigens (urine from individuals receiving therapeutic levels of the drugs), but not the native drugs. Only a few
ddab were reactive with granulocytes pretreated with the
drug (cell-
drug complexes); the majority of
ddab could not be detected unless the
drug or ex vivo
antigen was added to the incubation mixture as well as the
solution used for subsequent washes. Our results indicate that drugs and/or their metabolites interact with target cells and thereby directly function as immunogenic
haptens, even when the drugs do not bind tightly to the cells.