A spontaneously occurring complex of beta2-microglobulin and a fragment of gamma-chain of IgG: isolation from the urine of a patient with plasma cell leukemia and characterization.

A complex of a fragment of gamma-chain of IgG and beta2-microglobulin (beta2M) was isolated from the urine of a patient with plasma cell leukemia. The approximate m.w. of the gamma-fragment was 19,000 and this gamma-fragment was found to be associated with beta2M noncovalently. The complex could be dissociated in 7.5% (v/v) n-propanol which suggests an important role of hydrophobic bonds in the association of the gamma-fragment and beta2M. The beta2M did not bind monoclonal IgG from this patient. Several anti-beta2M antisera tested which had been prepared with free beta2M did not react with the beta2M associated with the gamma-fragment, but reacted with the free beta2M obtained by the dissociation of the complex.