[Antibody activities of monoclonal immunoglobulins].

Monoclonal immunoglobulins present a normal structure and have an antibody activity. This activity may be directed against exo-antigens especially bacterial, but more frequently against auto-antigens. It may then be symptomatic and therefore explain unusual clinical or biological manifestations in the course of monoclonal dysglobulinemias. The most common auto-antibody activities are directed against red blood cells (responsible for cold agglutinin disease), IgG (leading to the formation of cryoglobulinemia), and myelin (responsible for peripheral neuropathy). Often, the monoclonal auto-antibody activity is asymptomatic and polyspecific, as it is only the monoclonal expression of polyclonal natural auto-antibodies. Genetic study of variable segments of heavy and light chains used by these monoclonal antibodies are useful to precise the role played by antigen in the driving of the lymphoid proliferation. These physiopathologic models concerning monoclonal gammapathies are a useful tool to understand the physiopathology of polyclonal auto-immune disease and the role of auto-antibodies.