Lysozyme

Serum lysozyme has been proposed as a parameter for monitoring disease progression/regression in cases of proven sarcoidosis.² Revised FAB (French, American, British) criteria indicate that serum or urine lysozyme levels 3x normal fulfill one of three criteria for the presence of M4/M5 (acute myeloid leukemia with monocytic differentiation) vs M2 (acute myeloblastic leukemia with maturation).

Lysozyme, a hydrolytic enzyme and bacteriolytic glycosidase, when present in large amounts may appear as a far cathodal migrating (“cationic”) band on serum or urine protein electrophoresis. Lysozyme has been found in all three human neutrophil granules (azurophil, specific, and gelatinase types).³ It is elevated in some cases of myelogenous and in most cases of myelomonocytic and monocytic leukemia. The elevation is proportional to the degree of monocytic differentiation and to tumor cell burden and, if marked, can result in potassium wasting and hypokalemia.⁴ Lysozyme has been found within the granules of normal and leukemic eosinophils by immunoelectron microscopic study. Elevated serum lysozyme may not establish the presence of monocytic differentiation in cases of acute myelogenous leukemia with eosinophilia.⁵ The level of serum lysozyme has been used as a predictor of CNS involvement in these leukemias.⁶

Serum lysozyme has been shown to be elevated in a number of conditions, including tuberculosis and sarcoidosis as well as leukemia.² Sensitivity for prediction of sarcoidosis was 79% in a recent study (compare that of serum angiotensin-converting enzyme (ACE) at 59% in the same study).² The serum lysozyme level increased with the number of organs involved. Serum lysozyme, however, is less specific for sarcoidosis than serum ACE. When utilizing a turbidimetric method for measurement of serum lysozyme activity, there was evidence that such an assay was useful in differentiating infection from rejection in transplant recipients.⁷