A monoclonal antibody (MAb), MRK 16, specific to Adriamycinresistant human myelogenous leukemia cell line K562, was used to examine whether the antigen molecules (P-glycoprotein) recognized by the MAb are present in the adrenals. The materials examined included 61 human adrenals and several cell lines. Immunohistochemical analysis revealed that almost all of the human adrenal specimens (59 out of 61) were stained positively with MAb MRK 16 and that the antigen was strongly expressed even in cases where anticancer agents had not been given. Immunoprecipitation showed that the Mr 170,000–180,000 glycoprotein was present in all of the adult adrenals but not in fetal and neonatal adrenals. Furthermore, fluorescence image analysis revealed that the P-glycoprotein was more strongly expressed in the cortex than in the medulla, showing a tendency to occur in cell clusters in the latter area. The cell lines derived from animal adrenals (SW-13, Y-1, and PC-12) showed no positive staining with MAb MRK 16.

It is suggested that this glycoprotein may be related to maturation of the adrenal, in which it possibly plays a physiological role.

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