Turnover in humans of β2-microglobulin: the constant chain of HLA-antigens

The turnover of beta 2-microglobulin, the common subunit of the HLA antigens, has been examined in normal subjects and in some patients with kidney disorders, multiple myeloma and rheumatoid arthritis. All patients displayed elevated serum levels of beta 2-microglobulin. The plasma disappearance curve of 125I-beta 2-microglobulin demonstrated that the protein has a rapid turnover (t 1/2 = 2.1 h; range 1.1-2.8 h) in normal persons and in patients with a normal glomerular filtration rate. In patients with kidney disorders the impaired renal filtration prolonged the turnover time and led to elevated serum levels of beta 2-microglobulin. Simultaneous measurements of 125I-beta 2-microglobulin in serum and urine allowed estimations of the beta 2-microglobulin net reabsorption in the renal tubuli. Two patients with renal disease reabsorbed 84% and 89%, respectively, of the beta 2-microglobulin filtered in the glomeruli. In normal persons the net reabsorption is close to 100%. In patients with normal kidney function increased serum levels of beta 2-microglobulin seem to be due to an increased synthetic rate of the protein as the elimination rate is normal. HLA antigen heavy chains in serum are present in smaller amounts than beta 2-microglobulin. The present data, therefore, suggest an imbalanced synthesis of the two chains.