Analysis of islet antoantigens by the screening of a mouse islet cDNA expression library.

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Two clones were obtained by immunoscreening of an NOD mouse islet lambdagt11 expression library with prediabetic NOD mouse sera. The clones (C17 and C18) were recognized by NOD mouse sera but not by Balb/c mouse sera. Antibodies against C17 and C18 fusion proteins were detected in 80% and 10% of sera from 10 week-old female NOD mice, respectively. DNA sequences of C18 were identical to mouse chromogranin A cDNA (596-1892). Nucleotide sequences of C17 showed a poly (A) tail and open reading frame for 46 amino acids. C17 mRNA was detected by the Northern blot analysis in the pancreas and brain tissue. A nucleotide sequence with high homology with C17 was found in human pancreas cDNA.The sequence was cloned in a plasmid vector for further analysis. Antibodies to chromogranin A were measured by radioimmunoassays using as antigens in vitro transcribed and translated [^<35>S]-methionine-labeled mouse chromogranin A.The prevalence of anti-chromogranin A was approximately 10% in prediabetic female NOD mice. Whereas, the C17 antibody radioassay was not sensitive enough to measure titers of circulating antibodies. We also measured ICA512 (IA-2) antibodies in human subjects with the in vitro transcribed and translated [^<35>S]-methionine-labeled ICA512. The frequency of the ICA512 antibodies was higher in acute-onset IDDM than slowly progressive IDDM.The frequency and titer of ICA512AA declined sharply within 5 years after the onset of IDDM,suggesting the association of the antibody and acute beta-cell destruction.