title: Complement fixation by solid phase immune complexes. Reduced capacity in SLE sera.
abstract: We describe an ELISA for assessment of complement function based on the capacity of serum to support fixation of complement components to solid phase immune complexes (IC). Microplates were coated with aggregated bovine serum albumin (BSA) followed by rabbit anti-BSA IgG. The solid phase IC were reacted with human serum. The uptake of C3b, C4b and properdin was measured using biotinylated F(ab)2 antibodies to each of the proteins, avidin alkaline phosphatase, and paranitrophenyl phosphate. Serial samples obtained from 15 patients with systemic lupus erythematosus were investigated. Out of 72 sera, 24 showed a reduced capacity to support incorporation of C4b into solid phase IC. Thirty-one of the sera showed low C3b binding and 59 of the sera a reduced uptake of properdin. The incorporation into solid phase IC of C3b and C4b as well as of C3b and properdin were closely correlated at high disease activity. In general, patients with severe disease manifestations showed low values in the uptake assays. Judging from the results obtained by analysis of serial samples, the uptake of C3b, C4b and properdin, complement mediated solubilization of fluid phase IC and the concentrations of C1q binding IC were useful indicators of disease activity in the patients. The concentrations of circulating C4, C3 and properdin varied less consistently according to disease activity. The concentrations of serum properdin were never found to be low, which was in contrast to the finding of reduced properdin uptake by solid phase IC in most of the samples.
authors.affiliation: Institute of Medical Microbiology, University of Odense, Denmark.
authors.forename: G
authors.initials: G
authors.lastname: Baatrup
authors.forename: H
authors.initials: H
authors.lastname: Jonsson
authors.forename: A
authors.initials: A
authors.lastname: Sjöholm
authors.forename: G
authors.initials: G
authors.lastname: Sturfelt
authors.forename: S E
authors.initials: SE
authors.lastname: Svehag
mesh_terms: D000328:Adult; D000936:Antigen-Antibody Complex / Q000378:metabolism*; D003166:Complement Activating Enzymes / Q000378:metabolism; D003172:Complement C1 / Q000378:metabolism; D015922:Complement C1q; D003176:Complement C3 / Q000378:metabolism; D003179:Complement C3b / Q000378:metabolism; D003181:Complement C4 / Q000378:metabolism; D015935:Complement C4b; D003168:Complement Fixation Tests; D003165:Complement System Proteins / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000097:blood* / Q000276:immunology; D008297:Male; D008875:Middle Aged; D011414:Properdin / Q000378:metabolism; D012995:Solubility
chemical_list: D000936:Antigen-Antibody Complex; D003172:Complement C1; D003176:Complement C3; D003181:Complement C4; D011414:Properdin; D015922:Complement C1q; D003179:Complement C3b; D015935:Complement C4b; D003165:Complement System Proteins; D003166:Complement Activating Enzymes