Aggregated Human Immunoglobulins Bind to Modified Proteins

Human immunoglobulins treated at 55°C in vitro are able to interact with maleylated bovine serum albumin (mBSA), but not with unmodified BSA. Gel filtration experiments demonstrated that the mBSA binding is associated with a high molecular weight complex of aggregated IgG. This aggregated IgG with binding capacity for mBSA could also be generated in vitro by treatment of human IgG at 37°C or 40°C and by incubation with human neutrophils. Furthermore, IgG aggregates with binding activity for mBSA could be detected in untreated synovial fluids from rheumatoid arthritis patients, indicating that these complexes occur in vivo. The phenomenon of binding to aggregated IgG was extended to other modified proteins such as maleylated human serum albumin (mHSA), acetyl low density lipoprotein (Ac‐LDL) and BSA reacted with oxidized linolenic acid. Soluble forms of these modified proteins were able to compete for the interaction between aggregated IgG and surface‐bound mBSA. We also found that aggregated IgG enhanced the Ac‐LDL‐dependent foam cell formation. These findings suggest a role for aggregated IgG in the metabolism of oxidized proteins.