Immunoblot detection of BTK expressed in blood leukocyte populations from normal donors. Neutrophils were isolated from the blood by dextran sedimentation and Ficoll-Hypaque gradient centrifugation. CD3⁺ T cells, CD20⁺ B cells, CD16⁺ NK cells, and CD14⁺ monocytes were purified from mononuclear cells by electronic sorting. The cells were subjected to immunoblot analysis using anti-BTK or anti–β-actin MoAbs.