title: Quantitation of complement factor D in human serum by a solid-phase radioimmunoassay.
abstract: A sensitive solid-phase radioimmunoassay is described which quantitates human D to 1-2 ng/ml. The assay was used to measure the concentration of D in normal and acute-phase sera and sera from individuals with systemic lupus erythematosus. All 3 groups of sera had comparable levels of D with mean values of 1.8, 2.3 and 2.5 micrograms/ml, respectively. Also tested were sera decomplemented in vitro by activators of the classical and alternative pathways. The results indicated that D is not depleted by alternative or classical pathway activation. However, heat inactivation (56 degrees C, 30 min) of serum resulted in almost complete loss of antigenic D.
mesh_terms: D002097:C-Reactive Protein / Q000276:immunology; D003166:Complement Activating Enzymes / Q000032:analysis*; D003167:Complement Activation; D011416:Complement Factor D / Q000032:analysis* / Q000378:metabolism; D006461:Hemolysis; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D011863:Radioimmunoassay
chemical_list: D002097:C-Reactive Protein; D003166:Complement Activating Enzymes; C493488:CFD protein, human; D011416:Complement Factor D