Cystatin C Levels in Sera of Patients with Human Immunodeficiency Virus Infection. A New Avidin-Biotin ELISA Assay for Its Measurement

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Abstract
A solid-phase enzyme-linked immunosorbent assay (ELISA) for determining human serum cystatin C is described. In 50 normal samples, cystatin C concentration was 1247 /pm 224 μg/ L (mean /pm SD) which is in agreement with previously reported levels. Serum levels of cystatin C and β2-microglobulin (β2-M) were investigated in a time-course study during the development of human immunodeficiency virus (HIV) infection. We found a persistent and uniform increase in the β2-M concentration (2762 /pm 1239 μg/L). In contrast to β2-M, on the basis of cystatin C levels, we found two distinct populations, one of which demonstrated an increased concentration (1620 /pm 618 μg/L). Interestingly a second group (21% of patients) exhibited an initial significant decrease in cystatin C concentration with a mean value of 377 (range 55–850) μg/ L, followed by an increase. The biphasic pattern of cystatin C serum, a major cysteine proteinase inhibitor, during the course of HIV infection suggests a possible role for these proteinases (or proteinase inhibitors) in the development of this syndrome.