Previous studies have reported a neuroprotective role for cellular prion protein (PrPC) against apoptosis induced by serum deprivation in an immortalized prion protein gene deficient neuronal cell line. These cell lines were derived from Rikn-type prion protein gene-deficient (Prnp-/-) (type-2) mice, which produce a prion protein (PrP)-like glycoprotein named as doppel protein (Dpl). To conclude that PrPC inhibits apoptosis without Dpl, several immortalized cell lines were established from the brain of type-1 Prnp-/- mice (Zrch I). The data showed that PrPC had anti-apoptotic function in both neuronal and glial cells under serum free condition. On the other hand, the Prnp-/- cells expressed Dpl showed apoptosis as with Prnp-/- cells. The results suggest that the functions of PrP involve anti-apoptotic effect without reference to ectopic production of Dpl. Also to investigate whether PrP production effect neurite outgrowth of neuronal cell in vitro, the extension of the neurite was measured with time after passage. The PrPC expressed cells showed longer neurite outgrowth than that of Prnp-/- cells. The data suggest that PrPC affects the subsequent growth of neurite.