The catabolism of human G immunoglobulins of different heavy chain subclasses. 3. The catabolism of heavy chain disease proteins and of Fc fragments of myeloma proteins.

Abstract

The catabolism of (131)I and (125)I paired labelled Fc fragments of myeloma proteins and of H chain disease proteins of different heavy chain subclasses was studied in men and monkeys. In contrast to the previously demonstrated catabolic heterogeneity of intact γG immunoglobulins, the Fc fragments and H chain disease proteins of all subclasses tested were catabolized at a similar rate. These data suggest that structures not present on the Fc fragments are responsible for the faster turnover rate of γG(3) immunoglobulins and for the differences in half-lives of myeloma proteins within a given subclass. The catabolic features of the H chain disease proteins differed from those of intact γG. Although the whole body half-lives of the two proteins were similar, the fractional turnover rate of the H chain disease proteins was higher than that of γG, on the average 8% of the intravascular pool/day as compared to 4% for γG. One-half to 1% of the intravascular pool of the H chain disease protein and less than 0·1% of the γG was excreted into the urine. An average of 24% of the H chain disease proteins and 44% of the γG equilibrated into the intravascular compartment.