Neuraminidase increases DNA synthesis of spleen cells induced by native and asialylated erythropoietin.

The uptake of 3H-thymidine by a suspension of spleen cells, obtained from mice made anemic by phenylhydrazine injections, is increased above the values obtained with native human or mouse erythropoietin (Ep) if the hormone is enzymatically asialylated. Preparations of human Ep asialylated by mild acid hydrolysis stimulated DNA synthesis to a lesser extent than the native hormone; however, when neuraminidase was added to the culture medium, the stimulation exhibited by the asialylated Ep was not significantly different from the stimulation shown by the native hormone. The DNA synthesis of these cells is increased even more if neuraminidase and the asialylated hormone are added to the cell suspension. The asialylated Eps are not biologically active in vivo. The sialic acid moieties of Ep and of the cells responding to Ep are involved in the in vitro response of spleen cells to the hormone, possibly by making Ep receptors available to interact with the hormone.