Neuraminidase activity and free sialic acid levels in the serum of patients with acute poststreptococcal glomerulonephritis.

It has been suggested that in acute poststreptococcal glomerulonephritis, streptococcal neuraminidase may remove sialic acid from some normal plasma or tissue components, thus rendering it antigenic. We therefore investigated serum neuraminidase activity and serum and urinary free neuraminic acid levels, using the thiobarbituric acid method, in 39 patients with acute poststreptococcal nephritis. Serum neuraminidase activity was found in eight patients, and increased thiobarbituric acid-reactive material (presumed to be free neuraminic acid on the basis of absorption-spectrum similarity) was found in 28 patients. Serial determinations in 21 patients indicated that neuraminidase activity was present only initially and that free neuraminic acid levels decreased with time, usually becoming undetectable after four weeks. Determinations in patients with other renal and nonrenal diseases suggested that the findings were characteristic of poststreptococcal nephritis. Urinary neuraminic acid levels were unrelated to serum levels and were not markedly different between patients and normal subjects. These data suggest a role for neuraminidase activity in acute poststreptococcal nephritis, but they do not indicate whether it is primary or secondary.