Metabolism of radio-iodinated IgG in patients with abnormal serum IgG levels. I. Hypergamma-globulinaemia

Metabolic turnover studies were performed with radio-iodinated IgG in twelve patients with a serum IgG level greater than 1600 mg/100 ml (six with monoclonal gammopathy and six with a polyclonal increase in IgG associated with liver disease). The six patients with an IgG monoclonal protein comprised four multiple myeloma, one benign monoclonal gammopathy and one biclonal gammopathy presenting as Waldenström's macroglobulinaemia. The six patients with liver disease comprised two patients with cirrhosis, two with infective hepatitis and two with chronic active hepatitis. The injected IgG was either autologous normal IgG (five cases), autologous monoclonal IgG (five cases), homologous normal IgG (one case) or therapeutic intravenous HGG (two cases).

The plasma volume was increased in six patients; the plasma IgG pool in nine; and the total body IgG pool in seven. The plasma T½ was normal in one patient with monoclonal and one patient with polyclonal gammopathy but shortened in the other ten studies with mean values of 11·3 and 11·0 days in monoclonal and polyclonal gammopathy respectively. The fractional turnover rate was normal in two studies in polyclonal gammopathy and increased in the other ten with mean values of 13·6% per day in both groups of patients. The IgG synthesis rate was significantly increased in all studies except for a reduced synthesis of normal IgG in one patient with multiple myeloma. The mean synthesis rates in monoclonal and polyclonal gammopathy were respectively 6·7 and 4·1 times the mean synthesis rate in normal controls.

The pattern of increased synthesis and increased catabolism in such patients confirms published reports in some diseases and demonstrates a similar pattern in chronic active hepatitis. The findings are consistent with the `concentration-catabolism' effect.