Neuraminidase activity in human peripheral lymphocytes: its increase in chronic active liver disease

The activity of neuraminidase (sialidase) in peripheral white blood cells was measured by a fluorometric method using 4-MU NANA as a substrate. The activity in mononuclear cells, which was predominantly lymphocytes, was 2.5 times higher than that in polymorphonuclear cells (neutrophils). The former's activity was directly proportional to the number of the cells, but that of the latter was found to be suppressed by an increasing number of cells. Thus, the increased number of PMN contaminated in MNC fraction somewhat obscured neuraminidase activity affecting suppressively . The enzyme activity in MNC of 25 control subjects (15 males and 10 females) was 254 +/- 73 pmoles per hour per 10(6) cells and there was no difference between the values in males and females (233 +/- 59 vs. 284 +/- 81). The activity in 20 patients with chronic active liver disease was significantly higher than that in controls (551 +/- 135, p less than 0.01). The amount of sialic acid in MNC, which was 1.4 times more than that in PMN, revealed a tendency for a positive correlation between neuraminidase activity. A new finding of the increase of lymphocyte neuraminidase activity was introduced and its pathological significance particularly in liver disease was discussed.