Specific detection of monocytic lysozyme within normal and leukemic cells

A murine monoclonal antibody against human lysozyme (AHL MoAb) was produced and tested on normal and leukemic monocytes using flow cytometry. The antibody gave a positive reactivity on normal monocytes permeabilized by saponin (82% to 98% of positive cells) and a negative reactivity on normal permeabilized neutrophils. This monocyte-specific reactivity had not been observed using a polyclonal antibody. Nevertheless, immunoblotting detected lysozyme in both monocyte and polymorphonuclear leukocyte (PMNL) lysates. The AHL MoAb, in the presence of lysozyme substrate (Micrococcus lysodeikticus cell walls), strongly inhibited the enzymatic activity. Flow cytometric analysis of leukemic cells isolated from patients suffering from different subtypes of acute myeloid leukemia (French-American-British [FAB] classification FAB M1–5) showed a highly significant positivity of FAB M5 for lysozyme compared with the other subtypes. The present results were consistent with the detection of a lysozyme epitope by AHL MoAb located near the catalytic site in monocytes. The same epitope was probably masked in PMNL granules.