SERA FROM PATIENTS WITH IDDM AND HEALTHY-INDIVIDUALS HAVE ANTIBODIES TO ICA69 ON WESTERN BLOTS BUT DO NOT IMMUNOPRECIPITATE LIQUID-PHASE ANTIGEN

ICA69 is a recently cloned pancreatic islet protein proposed as a pote ntial target of autoimmunity in insulin dependent diabetes mellitus (I DDM). The aim of our study was to verify the relevance of ICA69 antibo dies as markers of the disease. We measured antibodies to ICA69 in ser a from newly-diagnosed IDDM patients, in age- and sex-matched normal c ontrols, and in sera prior to the onset of IDDM (pre-IDDM). Human isle t ICA69 was cloned and inserted into a bacterial expression vector and an in vitro transcription vector. Binding to affinity purified recomb inant ICA69 on Western blots was found in 33/48 (68%) sera from newly- diagnosed IDDM patients and in 36/56 (64%) controls. No differences in band intensity were found between IDDM and controls. Using immunoprec ipitation of S-35 methionine labelled in vitro translated ICA69, none of 53 sera from newly diagnosed IDDM patients, 0 of 57 control sera an d 1 of 24 pre-IDDM sera had detectable antibodies. We conclude that so lid-phase assays are inappropriate for measurement of ICA69 antibodies as specific markers of IDDM and that antibodies to ICA69 are not dete cted by a liquid-phase immunoprecipitation assay. These data support n either a role for ICA69 as a relevant autoantigen in IDDM, nor a role for the measurement of antibodies to ICA69 in the prediction of IDDM.