NUCLEAR ANTIGEN HISTONE H1 IS PRIMARILY INVOLVED IN LUPUS-ERYTHEMATOSUS CELL-FORMATION

Objective. To elucidate the nature of the antigen reactive with the '' lupus erythematosus (LE) cell factor,'' the autoantibody involved ire the LE cell phenomenon, Methods, Serum samples from systemic lupus ery thematosus (SLE) patients who were positive for the LE cell phenomenon (LEc+) and SLE patients who were negative for the LE cell phenomenon (LEc-) were used to characterize the nuclear antigen bound by the LE c ell factor, by immunoblotting and immunoprecipitation techniques. Resu lts. All LEc+ sera, hut none of the LEc-sera, uniformly reacted with a double band of MW similar to 30 kd in nuclear extracts, Depletion of nuclear protein extracts of antigens bound by pooled LEc- serum allowe d precipitation of a low molecular weight protein by pooled LEc+ serum . This protein was able to block LE cell formation by LEc+ serum, Base d on its reactivity with antihistone antibody and an electrophoretic m obility identical with that of precipitated and purified histone H1, t his protein was identified as histone H1. Moreover, all LEc+ sera, but none of the LEc- sera, reacted with purified histone H1 by immunoblot ting whereas other histones were reactive with both types of sera. In addition, purified histone H1, but none of the other histones, strongl y inhibited the induction of LE cells By LEc+ serum, Conclusion. Histo ne H1 represents the major antigenic component recognized by the LE ce ll factor, Thus, the LE cell phenomenon appears to be due primarily to anti-histone H1 reactivity.