Endogenous β-Galactosidase Activity in Continuously Nonproliferating Cells

Abstract Cytochemically detectable activity of endogenous β-galactosidase was found at pH 6.0 in Swiss 3T3 cells after long-term incubation in low serum or in the presence of heparin concentrations known to reversibly inhibit cell proliferation. A high percentage of β-galactosidase-positive cells were detected in U937 and HL60 cultures at the late stage of macrophage-like differentiation induced by TPA. Interestingly, a small number of β-galactosidase-positive cells were found even in the growing Swiss 3T3 cultures. These positive cells expressed morphological features similar to those of senescent cells. Thus, the activity of β-galactosidase at pH 6.0 cannot be considered an exclusive marker of senescent cells since it is expressed in other types of nonproliferating cells.