Immunoelectron microscopy.

Immunoelectron microscopy was performed using isolated bm MNCs prepared in one patient with AML with a high tryptase level (A; AML M4eo; serum tryptase, 881 ng/mL) and in one patient with AML with a lower tryptase level (B; AML M4; serum tryptase, 224 ng/mL). Immunogold labeling was performed using anti-tryptase mAb G3 (for technical details see text). In the patient with elevated serum tryptase levels, G3-reactive material was detected in the (small) cytoplasmic compartment of AML blasts. Interestingly, tryptase was often found to localize to granulelike structures (A). Cases without elevated serum tryptase were consistently negative by immunoelectron microscopy (not shown).