Relationships between antinuclear and anti-Ro/SS-A antibodies in subacute cutaneous lupus erythematosus

A certain degree of confusion has arisen regarding the relationship between patients having subacute cutaneous lupus erythematosus (SCLE) and those with “antinuclear antibody-negative” systemic lupus erythematosus (ANA-negative SLE). One of the confusing issues relates to published differences in the autoimmune serologic findings of these two patient groups. In order to clarify this issue, we have screened the sera from thirty-seven patients with SCLE for the presence of fluorescent antinuclear antibodies (FANA) on two different substrates—human Hep-2 tissue culture cells and mouse kidney sections. In addition, these same sera were assayed for anti-Ro/SS-A precipitin antibodies. Seventy-eight percent of the sera were FANA-positive at a titer of 1:10 or greater when tested on human Hep-2 cells, whereas 76% were positive at a titer of 1:80 or greater. Fifty-one percent were positive on mouse kidney sections at a titer of 1:10 or greater, whereas 46% were positive at a titer of 1:20 or greater, Twenty-two percent of these sera were completely FANA-negative on both human and mouse substrates. None of these sera that were negative on both substrates contained anti-Ro/SS-A antibodies. However, 69% of the sera that were FANA-positive on both human and mouse substrates were found to have detectable anti-Ro/SS-A antibodies. Ninety percent of the SCLE sera that were FANA-positive on human Hep-2 cells, but negative on mouse kidney sections, contained anti-Ro/SS-A antibodies. These sera gave a speckle-like, or particulate, nuclear immunofluorescence staining pattern. These results demonstrate that the ability to detect FANA in patients with SCLE depends greatly on the type of substrate used in the FANA test, and they confirm that human Hep-2 cells provide a more sensitive FANA substrate than do mouse kidney sections. In addition, a positive FANA on Hep-2 cells that is negative on mouse kidney sections strongly suggests the presence of Ro/SS-A antibodies in patients with SCLE. These findings also demonstrate that serologic differences between SLE patient groups that share similar clinical features can be due to differences in the substrates used in performing the FANA test.