IgG and IgM autoantibody differences in discoid and systemic lupus patients.

Systemic lupus erythematosus (SLE) patients with discoid lupus erythematosus (DLE) were reported to have milder disease. To test this observation, we used sandwich arrays containing 98 autoantigens to compare autoantibody profiles of SLE subjects without DLE (DLE-SLE+) (N=9), SLE subjects with DLE (DLE+SLE+) (N=10), DLE subjects without SLE (DLE+SLE-) (N=11), and healthy controls (N=11). We validated differentially expressed autoantibodies using immunoassays in DLE-SLE+ (N=18), DLE+SLE+ (N=17), DLE+SLE- (N=23), and healthy subjects (N=22). Arrays showed 15 IgG autoantibodies (10 against nuclear antigens) and 4 IgM autoantibodies that were differentially expressed (q-value<0.05). DLE-SLE+ subjects had higher IgG autoantibodies against double-stranded DNA (dsDNA), single-stranded DNA (ssDNA), double-stranded RNA (dsRNA), histone H2A and H2B, and SS-A (52 kDa) compared with all other groups including DLE+SLE+ subjects (P<0.05). Immunoassays measuring anti-dsDNA, -ssDNA, and -SS-A (52 kDa) IgG autoantibodies showed similar trends (P<0.05). Healthy and DLE+SLE- subjects expressed higher IgM autoantibodies against alpha beta crystallin, lipopolysaccharide, heat-shock cognate 70, and desmoglein-3 compared with DLE+SLE+ and DLE-SLE+ subjects. IgG:IgM ratios of autoantibodies against nuclear antigens progressively rose from healthy to DLE-SLE+ subjects. In conclusion, lower IgG autoantibodies against nuclear antigens in DLE+SLE+ versus DLE-SLE+ subjects suggest that DLE indicates lower disease severity. Higher IgM autoantibodies against selected antigens in healthy and DLE+SLE- subjects may be nonpathogenic.