Constitutive expression of RET protein in purified human normal neutrophils, as detected by immunocytochemistry (A and B), and in CD14⁺ PB monocytes, as detected by Western blotting (C). (A) Neutrophils stained with affinity-purified nonimmune rabbit serum (0.1 μg/mL). (B) Neutrophils stained with affinity-purified rabbit polyclonal antibodies recognizing the RET tyrosine-kinase domain (0.1 μg/mL). Original magnification for (A) and (B) × 400. (C) Western blot analysis of RET protein in human normal monocytes. Proteins extracted from purified CD14⁺ PB monocytes, THP-1 (positive control), and undifferentiated U937 (negative control) cell lines were immunoprecipitated with two antibodies (Ab 1 and Ab 2) recognizing different cytoplasmic domains the RET RTK, blotted onto immobilon-P membranes, and shown by standard chemiluminescence.