Determination of lysozyme in serum, urine, cerebrospinal fluid and feces by enzyme immunoassay.

Conjugates of human lysozyme and horseradish peroxidase (HRP) were prepared by means of the heterobifunctional reagent N-succinimidyl 3-(2-pyridyldithio) propionate. A conjugate containing 2 mol HRP/mol lysozyme was isolated by gel filtration and used as a labeled antigen in competitive enzyme immunoassays, in which anti-lysozyme rabbit IgG had been bound to wells of microtiter plates. The assay can detect as little as 1 microgram lysozyme/l. The following reference intervals have been established: 950-2450 micrograms/l for serum, 1.7-123 micrograms/l for urine, 17.6-118 micrograms/l for cerebrospinal fluid and 0.04-1.5 microgram/g for feces.