Preparation of a defined immune complex for use in C1q binding assays.

Soluble immune complexes of human beta 2 microglobulin with its IgG antibodies from Macaca irus antisera have been tested for suitability as a reference preparation for immune complex assays in human disease. The defined complex described is stable on storage, behaves reproducibly in a C1q solid phase binding assay and fulfills the criteria required for an international reference standard.