A SUBGROUP OF MURINE MONOCLONAL ANTI-DEOXYRIBONUCLEIC ACID ANTIBODIESTRAVERSE THE CYTOPLASM AND ENTER THE NUCLEUS IN A TIME-DEPENDENT AND TEMPERATURE-DEPENDENT MANNER

BACKGROUND: The capacity of lupus autoantibodies to enter living cells and bind to molecules for which they have intrinsic affinity is not w ell appreciated. In previous studies, we identified a subgroup of thre e murine monoclonal IgG anti-DNA antibodies, derived from lupus-prone MRL-lpr/lpr mice, that localized within nuclei of cells in multiple or gans and induced functional perturbations, in vivo, after passive tran sfer to normal mice. To examine the mechanisms of this phenomenon, we now extend these observations, using the same monoclonal anti-DNA anti bodies and cultured cell lines. EXPERIMENTAL DESIGN: Multiple experime ntal approaches mere utilized to track nuclear localization of anti-DN A antibodies, including direct immunofluorescence, confocal microscopy and immunoelectron microscopy. The requirements for nuclear localizat ion were further evaluated quantitatively, in nuclei isolated from co- cultures of cells and I-125-Ig, under varying experimental conditions. RESULTS: Nuclear localization was observed with the same subset of an ti-DNA antibodies that localized within nuclei in vivo; it was depende nt on the antigen-binding region of the molecule; and it was not found with other anti-DNA antibodies. At progressive intervals, the Ig were observed: at the cell surface, within the cytoplasm, clustered at the nuclear pore, and within the nucleus. Nuclear localization of Ig was found to be a time- and temperature-dependent process, specific for a subset of anti-DNA antibodies and dependent on the antigen binding reg ion of the Ig. CONCLUSIONS: This is the first demonstration that monoc lonal autoantibodies can traverse both the cell and nuclear membranes to localize within the nuclei of cultured cells. Furthermore, nuclear localization of Ig was regulated in a manner analogous to that of othe r large cytoplasmic proteins that enter the nucleus. This confirms and extends our results using the same antibodies in whole animals, and i t provides the basis to further examine the underlying mechanisms and consequences of this phenomenon.