A soluble acidic protein of the cell nucleus which reacts with serum from patients with systemic lupus erythermatosus and Sjögren's syndrome.

A soluble nuclear antigen that reacts with sera obtained from patients with systemic lupus erythematosus and Sjögren's syndrome has been described. The antigen, tentatively named the Ha antigen after the prototype serum, was shown to react with specific antibodies by precipitin, complement fixation, and immunofluorescence techniques. The Ha antigen prepared from isolated nuclei of calf thymus glands, calf liver, and rat liver showed identical immunological reactivities; a wide distribution among different species and tissues is presumed. The Ha antigen was destroyed by trypsin and relatively mild heat or pH variation from neutrality, but was resistant to DNase or RNase. Many of these characteristics are similar to those of the "B" antigen to which antibodies have recently been described in Sjögren's syndrome. The nuclear origin of the Ha antigen was confirmed by the speckled nuclear immunofluorescence staining pattern given by purified antibody to Ha obtained from a specific immune precipitate. Preliminary results showed approximately 13% of patients with systemic lupus erythematosus and 30% of patients with Sjögren's syndrome had precipitating antibodies to the Ha antigen.