Immunomorphologic characterization of SpA-Sepharose beads exposed to monomeric, aggregated, and immune complex-bound human IgG

Staphylococcal protein A (SpA)-coupled gels have recently been used to eliminate or isolate immune complexes from patients. In this study we could show, by using immunofluorescence technology, that soluble heat-aggregated human IgG and tetanus/antitetanus immune complexes only reached the outer part of the beads of a SpA-Sepharose MB gel. This indicates that the exclusion limits are altered after coupling with the SpA-ligand. The higher avidity of immune complexes, compared to monomeric IgG, is not efficiently used since only monomeric IgG can reach the interior of the beads. Finally, the results point to the importance of using a solid matrix with a large surface area where the SpA-molecules are available for the immune complexes.