ANTIBODIES TO THE 37,000-MR TRYPTIC FRAGMENT OF ISLET ANTIGEN WERE DETECTED IN JAPANESE INSULIN-DEPENDENT DIABETES-MELLITUS PATIENTS

Sera from 30 Japanese insulin-dependent diabetes mellitus (IDDM) patie nts of short duration were examined to determine whether they had anti bodies to proteolytic fragments of islet antigen, the molecular weight s of which were 37,000 and/or 40,000 Mr (37KAb). The median age and di sease duration of the patients were 13 (range; 6-22) years old and 12 (range; 0-24) months, respectively. Twelve out of the 30 IDDM patients (40%) had 37KAb, while none of the 16 control subjects was positive f or 37KAb. The frequency of the 37KAb was not correlated with disease d uration tested. We further investigated the antibodies to ICA512, by r adioligand binding assay, which has been proposed to be a target antig en for the 37KAb. Twenty-two (73.3%) patients had antibodies to ICA512 (ICA512AA), but none of the control subjects did. The levels of ICA51 2AA, which were described as indexes using standard sera, were signifi cantly higher in the patients than in the control subjects (1.436 +/- 2.674 and 0.001 +/- 0.002, respectively, P<0.05). The frequency of ant ibodies to glutamic acid decarboxylase 65 (GAD65Ab) was also higher in the patients than in the control subjects (70% and 0%, respectively), but 7 out of 9 GAD65Ab-negative patients had ICA512AA and/or 37KAb. S ince 93% of the IDDM patients had at least one of these antibodies, co mbined analysis with 37KAb, ICA512AA, and GAD65Ab facilitates diagnosi s of Japanese IDDM.