Proteolysis of human IgG by human polymorphonuclear leucocyte elastase produces an Fc fragment with in vitro biological activity.

The Fc fragment derived by proteolysis of human IgG by human polymorphonuclear leucocyte (PMN) elastase was tested for in vitro biological activity. This fragment could attach to the specific IgG receptor of Staphylococcus aureus Cowan I cells (protein A) and could be eluted from the cells with dissociating buffer. Taking advantage of this attachment, it was shown that the Fc fragment is capable of attaching to the antigen-combining site of an IgM rheumatoid factor and can bind to the Fc receptor of human PMN. A similar fragment produced in vivo at sites of inflammation could play a role in regulating the inflammatory response.