Autoantibodies in the sera from newly diagnosed diabetic nod mice: evidence against cross-reactivity with a putative beta-cell surface autoantigen.

In insulin-dependent diabetes mellitus in humans, the BB rat and the NOD mouse, serum has been reported to contain autoantibodies that precipitate a 64,000 Mr protein from (32S) methionine labeled histoincompatible non-autoimmune rat or mouse islet cell proteins. Because experimental data reported recently have brought into question the role of the 64,000 Mr protein in targeting autoantibodies and hence initiate beta-cell destruction, we report differently designed experiments to clarify the apparent 64,000 Mr autoantigen enigma. Using an in vitro model of NOD mouse origin mimicking diabetic insulitis we found that target beta-cells induced a 6-fold increase in proliferative response of splenic L3T4+, Thy-1,2+ T cells. The magnitude of the proliferative response was not affected when target beta-cells were pretreated with 50% (vol/vol) partially purified immunoglobulins ((NH4)2SO4 precipitation at 33% saturation) from sera from newly diagnosed (less than 4d after onset) diabetic NOD mice. Cytofluorimetric analysis of beta-cells pretreated with partially purified immunoglobulins plus FITC-conjugated goat antimouse IgG as a second-step antibody were negative and thus gave no indication of an autoantigen-autoantibody complex formed on the surface of the beta-cells. We conclude from the experimental data that it remains still in question whether an autoantigen is targeted by an islet cell surface specific autoantibody and plays a role as a triggering event in the pathogenesis of diabetes in NOD mice.