Clq binding activity in lupus erythematosus: correlation with the "lupus band test".

A 131I C1q binding assay was employed to estimate C1q binding activity (C1q BA), presumably due to the presence of circulating immune complexes, in lupus erythematosus sera. Thirteen of 16 sera from patients with systemic lupus erythematosus (SLE) had elevated C1q BA. Only 1 of 17 sera from patients with generalized discoid LE (GDLE) and none of 5 localized DLE patient's sera had elevated C1q BA. A correlation between a positive LE band test and the level of C1q BA was apparent. A positive LE band test tended to occur in patients with higher levels of C1q BA, whereas a negative LE band test tended to occur in patients with low levels of C1q BA.