Tissue bound immune complexes are demonstrated by immunofluorescent technique with specific fluorescein-labelled anti-IgG or anti-IgA or by cryo-EM. Present upon local formation or deposited from the circulation, neither way is proof for their pathogenic role; proof comes from detection of the cognate antigen by in situ hybridization.
The soluble circulating CIC are usually detected by ELISA technology; efforts to use mass spectrometry MS /LC-MS have not (yet) found their way into routine. Complement components bound to IC may be used as capture: detection of C4 and/or C5 bound to CIC can directly serve to identify those IC that have pushed complement activation beyond C3.
Monoclonal antibodies against C1q are fixed to polystyrol plates capturing C1q bound to complexes which then are revealed by enzyme labeled anti-IgG antibodies. Methods may use cellular Fc-receptor interaction of the IC .
Immune complexome analysis spots on antigens in purified ICs: nanoliquid chromatography combined with electrospray ionization/tandem MS can identify compounds at the origin of the conflict, e.g. citrulline-containing protein in rheumatoid arthritis or thrombospondin-1 (THBS 1).
On the way to apply single particle cryo-electron microscopy (cryo-EM) using affinity grids IC dectection and identification of its components might enter a new era. Results will soon enter big data warehouses but wait semantic uniformity using LOINC coding.
Decline in CIC serum concentration reflects therapeutic efficacy. In vitro, nephelometry or immunfixation gel electrophoresis IC use formation dynamics between specific antibodies and antigen to be quantitated, such as free light chains (FLC) kappaλ
Cave: methods which are subject to optimal antigen-antibody ratio might miss high amounts of antigen in antigen excess.