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

摘要

The catabolism of ¹³¹I and ¹²⁵I 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 γG3 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.