Antibody effector functions other than neutralization depend on interactions with soluble and cellular components of the immune system. Antigen recognition is usually oligoclonal, with the different clones of antibodies belonging to different classes, subclasses, glycoforms and having different affinities and epitope specificities. Thus, composition of immune complexes determines biological effects mainly via interactions with FcR and complement proteins. Antibodies are capable of triggering any of the three pathways of complement activation and antigen recognition of complex antigens often results in the activation of more than one pathway. These events can be tracked in a multiplex format using antigen microarrays, where complement products bind to elements of the microarray. By controlling cation concentrations and detecting various complement components (C1q, C4, C3) contribution of the different pathways can be identified. Parallel measurement of antibodies and complement proteins provides a novel way of looking at interactions between antigen and antibodies. We propose the use of immune complex signatures, composite depictions of antibody and complement content of immune complexes characterizing healthy and diseased populations. Normalized interquartile ranges of antibody binding (IgM, IgG) and complement deposition (C4, C3) are projected onto radar charts to produce patterns that can distinguish normal and altered immune responses. We propose that comprehensive interaction studies of serum antibodies and complement with arrays of antigens can generate functional antibody profiles and help better understand immunological disease mechanism.
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