Studies on β2-microglobulin. I. On its Immunochemical Properties and the Clinical Results Determined by Radioimmunoassay

A low molecular weight β2-microglohulin (β2μ) was isolated from urine of tubular proteinuria and its immunochemical properties were investigated. Serum levels and urinary excretion ofβ2μ were determined in healthy control and patients with various renal dysfunction by radioimmunoassay. The following results were thus obtained. 1) The mean values of serum β2μ of control subjects were 1.40 μg/m? in subjects under sixty and 2.28 μg/m? in persons over sixty, respectively. No difference between male and female was found. About half of the elderly persons surveyed had mild hypertension. However, no definite influence of the mild hypertension was seen on the increase of β2μ levels. The serum levels showed a tendency to increase with aging, and a correlation was found between serum β2μ and serum creatinine levels. It was suggested that the relatively high levels of serum β2μ in elderly persons might he related to the decrease of the glomerular filtration rate. 2) The mean values of urinary β2μ and urinary excretion ratio of β2μ/total protein determined in spot urine specimens from healthy subjects under sixty were 0.07 μg/m? and 0.28%, respectively. These values showed a fair increase in elderly persons in contrast to younger adults. There was influence of mild hypertension on their urinary levels in elderly persons. However, there was no difference on the amounts of urinary total protein between younger adults and elderly persons. It was, therefore, suggested that the effects of aging may be involved in the reduction of tubular function. 3) In renal disorders, it was suggested that quantitative determinations of β2μ and excretion of β2μ/total protein in spot urine specimens would be useful for the detection of tubular proteinuria. 4) Apparently increased urinary levels of β2μ in patients with multiple myeloma and other malignancies were seen. It was suggested that the results might reflect the increased serum concentrations of β2μ in these malignancies to some extent. 5) Depositions of β2μ in renal tubular cells were demonstrated by the immunofluorescent technique, suggesting that the metabolic site of β2μ in the kidney might he the renal tubules