H. Keilacker et al., AUTOANTIBODIES TO INSULIN AND TO PROINSULIN IN TYPE-1 DIABETIC-PATIENTS AND IN AT-RISK PROBANDS DIFFERENTIATE ONLY LITTLE BETWEEN BOTH ANTIGENS, Hormone and Metabolic Research, 27(2), 1995, pp. 90-94
To answer the question whether insulin or proinsulin would be the true
antigen for both insulin and proinsulin autoantibodies, displacement
experiments of I-125-insulin and -proinsulin binding with both unlabel
ed antigens were performed in sera of four groups of antibody-positive
probands: first-degree relatives of Type 1 diabetic patients, pre-Typ
e 1 diabetic persons, recent-onset Type 1 diabetic patients, insulin-t
reated Type 1 diabetic patients. In subjects who were primarily screen
ed to constitute these groups, prevalences of insulin and proinsulin a
utoantibodies were nearly identical. In antibody-positive sera, I-125-
insulin and -proinsulin binding values in general were closely correla
ted to each other with regression coefficients near 1.0. In all groups
of probands, mean values of I-125-insulin and -proinsulin binding did
not significantly differ. With the exception of a few sera, insulin a
nd proinsulin antibodies differentiated only little between both antig
ens. Epitopes of the insulin molecule are therefore preferred. Neverth
eless, insulin and proinsulin autoantibodies are not completely identi
cal nor are insulin autoantibodies merely a subgroup of proinsulin aut
oantibodies: In each group, in the mean, insulin antibodies as well as
proinsulin antibodies reacted somewhat (but significantly) stronger w
ith their respective antigen. In some cases a distinct (relative) spec
ificity for either antigen of insulin and proinsulin autoantibodies we
re observed, the latter being still present after some months of insul
in treatment. In conclusion, despite detectable differences in antigen
specificity, insulin and proinsulin autoantibodies seem to be equally
potent markers of Type 1 diabetes mellitus.