IGG4 BINDING-FACTOR IN HUMAN SEMINAL PLASMA IDENTIFIED AS HEAVY-CHAINOF IMMUNOGLOBULIN

Human seminal plasma contains a factor that binds human immunoglobulin G (IgG). The factor has an estimated M(r) of 50 kD and interacts spec ifically with human IgG4. It does not bind other subclasses of human I gG or IgGs of other mammalian species tested, The factor was purified by affinity chromatography on protein G column. The 50-kD component wa s eluted in the adsorbed fraction and immunostained with monoclonal an tibodies against heavy chain (gamma) of IgG. Purified subclasses of hu man serum IgG were separated into heavy and light chains by sodium dod ecyl sulfate polyacrylamide gel electrophoresis under reduced conditio n. The heavy chains of all subclasses of IgG bound IgG4. The present f indings suggest that the 50-kD IgG4 binding factor of human seminal pl asma is the heavy chain of IgG.