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

Abstract. The turnover of β2-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 β2-microglobulin. The plasma disappearance curve of 125I-β2-microglobulin demonstrated that the protein has a rapid turnover (11/2 = 21 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 β2-microglobulin. Simultaneous measurements of 125-β2-microglobulin in serum and urine allowed estimations of the β2-microglobulin net reabsorption in the renal tubuli. Two patients with renal disease reabsorbed 84% and 89%, respectively, of the β2-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 β2-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 β2-microglobulin. The present data, therefore, suggest an imba-lanced synthesis of the two chains.