Amplifying elements in erosive processes. Immune complexes (IC's) generate high levels of IL-1 and, through Fc interaction, also provide additional mediators to activate pro-metalloproteinases (MMPs). T cells might be involved in enhanced bone erosion through TNF, IL-17 and the direct production of osteoprotegerin ligand (OPG-L). T cells come close to the bone at erosion sites. IL-17 also promotes cartilage erosion; a role for OPG-L in this remains to be determined. Fc Rec, Fc receptor; LT, lymphotoxin; PMN, polymorphonuclear cell.