SPONTANEOUSLY PRODUCED ANTI-DNA DNASE-I AUTOANTIBODIES MODULATE NUCLEAR APOPTOSIS IN LIVING CELLS/

Apoptosis has received increased attention over the past decade, and i t is established as an essential process in physiological and disease states. Much effort has been devoted to understanding the intracellula r mechanisms culminating in apoptosis; intense investigation has also focused on its role during inflammation. Despite these efforts, these events remain incompletely understood. It has been suggested that the Ca2+- and Mg2+-dependent endonuclease that mediates DNA fragmentation is DNase I; however, the precise role of DNase I during apoptosis has been debated. Recent observations using anti-DNA antibodies derived fr om autoimmune mice (MRL-lpr/lpr) provided both the means and the reage nts to approach these issues in a more direct manner. We previously di scovered that many anti-DNA antibodies cross-react with DNase I, and a subset of these Ig inhibited DNase I enzymatic activity in vitro. Ser endipitously, in separate studies, a subset of these antibodies were o bserved to enter and localize within the nuclei of living cells. The a im of the present investigation was to determine whether these nuclear -localizing anti-DNA antibodies could interact with DNase I in living cells. We found that, once internalized, these autoantibodies bound DN ase I and inhibited activity of the enzyme. Furthermore, living cells containing the intracellular antibodies appeared resistant to apoptoti c stimuli; both morphological features of nuclear apoptosis and DNA fr agmentation were inhibited. These results support a pivotal role for D Nase I in apoptosis, and they provide a novel paradigm for autoantibod y-mediated inflammatory disease.