Metabolism of radio-iodinated IgG in patients with abnormal serum IgG levels. II. Hypogamma-globulinaemia.

The metabolism of radio-iodinated IgG was studied in seven patients with IgG deficiency (<600 mg/100 ml). The group comprised two patients with primary hypogamma-globulinaemia, one with primary hypogamma-globulinaemia and nodular lymphoid hyperplasia, and one each with chronic lymphatic leukaemia (CLL), γG multiple myeloma, renal homotransplantation and the nephrotic syndrome. All patients had markedly reduced plasma and total body pools of normal IgG with normal distribution (intravascular and extravascular pools). An increase in the initial urinary excretion of free isotope in one patient was attributed to a degree of protein denaturation. Compared to the normal range of 20–60 mg/kg/day for IgG synthesis, the patients with primary deficiency and the patient with CLL all had markedly reduced synthesis of normal IgG (2, 5, 4 and 7 mg/kg/day respectively). These patients also had a prolonged or normal plasma T½ and a normal or decreased fractional turnover rate (FTR). The patients with deficiency of normal IgG secondary to multiple myeloma, renal homotransplant or nephrotic syndrome all had an IgG synthesis rate at the lower limit of the normal range with values of 19, 21 and 19 mg/kg/day respectively. They had increased catabolism with a short plasma T½ and increased FTR. An assessment of the factors controlling the metabolism of normal IgG is important in the individual patient as regards the management of their recurrent infections with therapeutic human γ-globulin.