To achieve specific removal of pathogenic antibodies (Ab) or immune complexes (IC), several adsorbers have been developed. We discuss the mode of action of low-throughput staphylococcal protein A (SPA) immunoadsorption. The SPA-based Prosorba apheresis is likely to modify some of the autoantibodies (autoAb) or IC. The low-throughput adsorber showed very limited adsorption capacity of circulating autoAb and/or circulating IC. Besides changes of humoral diagnostic parameters, cellular changes could be observed in the Prosorba-treated patients. These changes were rather similar to those that have been observed in a patient successfully treated with Ab against tumor necrosis factor alpha. We propose an adsorber-catalyzed conversion of small, tissue-penetrating, scarcely detectable, non-complement-binding, proinflammatory IgG-rheumatoid factor (RF)-based IC into the more readily phagocytosed species of IC: intermediate-sized, partially cryoprecipitable, non-tissue penetrating IC that are opsonized with complement. These IC are rather short-lived and could quickly be cleared by the body's scavenging system.