A monoclonal antibody 5E5 recognizes an intranuclear antigen selectively present in a subpopulation of the neurons

Monoclonal antibody 5E5 labeled the nuclear antigen of the neurons in the guinea pig and rat central nervous systems including the cerebrum, cerebellum, spinal cord and retina. This antibody could discriminate neurons even among the same cell class. In in vitro study, only 10% of dividing PC12 cells was labeled with this antibody. An electron microscopic immunohistochemical study also revealed that this antibody selectively labeled heterochromatins in the neurons. Although we could not obtain any positive result by an immunoblot study, the antigenicity was remarkably diminished by the DNase I or S1 nuclease treatment on the tissue sections whereas RNase and trypsin was ineffective. These results suggested that this antigen might be a single-stranded DNA-protein complex resistant to proteolytic procedures, and possibly related to cell function or state of differentiation.