Fibronectin in cryoimmunoglobulinaemias.

Isolated and washed cryoimmunoglobulins from 15 patients were studied for the presence of fibronectin by immunodiffusion tests. Two of the isolated cryoglobulins proved to the pure monoclonal immunoglobulins (IgGl kappa and IgGl lambda), nine contained both monoclonal IgM kappa and polyclonal IgG and four were composed of polyclonal IgG, IgM and IgA by immunoelectrophoresis. Double immunodiffusion analysis detected the presence of fibronectin in each of the separated cryoimmunoglobulins. In a solid phase radioimmunoassay, I125 labelled purified fibronectin proved to bind to isolated human monoclonal myeloma proteins of IgGl kappa and IgG3 lambda subclasses. Fibronectin seems to be present not only in mixed polyclonal but also in mixed monoclonal-polyclonal and in monocomponent cryoimmunoglobulins, and it may be bound to one of the immunoglobulin components of the cryoglobulins.