Factors influencing immune complex localisation.

In systemic immune complex (IC) diseases such as SLE and rheumatoid vasculitis, IC accumulate in a number of tissues, either after deposition from the circulation or from in situ formation. The tissue localisation of IC depends on a delicate balance between the production of IC and the ability of the mononuclear phagocytic system (MPS) to remove them from blood. At times IC are cleared inefficiently, persist in the circulation and subsequently localise in tissues. This review evaluates the role of local tissue factors - anatomical, physiological, physical and immunological - in this process. We report on our studies examining the significance of C3b and IgG Fc receptors in tissues subject to IC deposition. No evidence for such receptors was found with the exception of a C3b receptor in human glomeruli. Our negative findings may be due to methodological difficulties in the identification of in situ receptors. Alternatively, immune receptors may not be present at these extra-glomerular sites and would therefore be unlikely to participate in IC localisation.