Comparison of IgG subclass autoantibodies in patients with systemic lupus erythematosus and subacute cutaneous lupus erythematosus.

Circulating antinuclear antibodies and in vivo bound immunoglobulins at the dermal-epidermal junction are frequently seen in patients with lupus erythematosus. The present study was designed to examine the distribution of the IgG subclasses of in vivo skin bound IgG and circulating antinuclear antibodies (ANA) in patients with systemic lupus erythematosus (SLE) or subacute cutaneous lupus erythematosus (SCLE). Immunofluorescence studies on skin biopsies showed IgG1 to be the predominant IgG subclass in SCLE patients, present in 20 of 21 (95%) of the specimens. IgG2 was present in 4 patients (19%), IgG3 in 1 (5%), and IgG4 in 7 (33%). The frequencies of IgG2, IgG3, and IgG4 skin staining were significantly higher in the seven SLE patients who were studied: IgG1 in 7/7 (100%), IgG2 in 7/7 (100%) and IgG4 in 6/7 (86%). Immunoblot analysis for the IgG subclasses was performed on serum of 29 patients with SCLE who had antibodies to SSA/Ro antigen. Twenty-seven (93%) of these patients were positive for IgG1 anti-SSA/Ro antibody, while the frequencies for IgG2, IgG3, and IgG4 anti-SSA/Ro were very low. These studies indicate that there is a difference in the IgG subclass antibody response in patients with SLE and SCLE. The presence of more than one subclass antibody may be indicative of systemic disease.