title: Assay, purification and further characterization of 7S C1q-precipitins (C1q-p) in hypocomplementemic vasculitis urticaria syndrome and systemic lupus erythematosus.
abstract: C1q-precipitins (C1q-p) are comprised of 7S IgG with C1q-binding activity found in sera of patients with hypocomplementemic vasculitis urticaria syndrome ( HVUS ) and systemic lupus erythematosis (SLE). We have utilized C1q-coated polystyrene beads to selectively isolate C1q-p and to establish a sensitive and quantitative assay of C1q-p and immune complex activity. Purified C1q-p was comprised of polyclonal IgG which retained 7S sedimentation and solid phase C1q-binding activity at physiological ionic strength both in the presence and absence of normal human sera. No precipitation interaction was observed between C1q-p and fluid-phase C1q or C1 under the conditions tested. Purified C1q-p had no activity in the Raji cell immune complex activity. C1q-p activity also was observed in and purified from SLE serum; this activity was distinguishable from 7S immune complex activity detected by Raji cells which was also present in SLE serum. These studies indicate that C1q-p is a 7S IgG molecule found in HVUS as well as some SLE sera and has activity in C1q-binding but not in Raji cell-binding immune complex assays. These data also suggest that C1q-p is a monomeric, polyclonal IgG with preferential affinity for bound C1q. In addition to its potential role in immune complex disease, C1q-p may also provide an important tool for studying the interaction of immunoglobulin and C1q, and should contribute important information to understanding the pathobiology of immune complex disease.
mesh_terms: D000936:Antigen-Antibody Complex / Q000302:isolation & purification; D003166:Complement Activating Enzymes / Q000302:isolation & purification*; D015922:Complement C1q; D003165:Complement System Proteins / Q000172:deficiency*; D006801:Humans; D007163:Immunosorbent Techniques; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D011863:Radioimmunoassay; D013577:Syndrome; D014581:Urticaria / Q000276:immunology*; D014657:Vasculitis / Q000276:immunology*
chemical_list: D000936:Antigen-Antibody Complex; D015922:Complement C1q; D003165:Complement System Proteins; D003166:Complement Activating Enzymes