In vitro expression of erythroid differentiation induced by Friend polycythaemia virus

WITHIN a few days after infection of susceptible mice with the Friend polycythaemia virus (FVP), a large increase in red cell production occurs leading to polycythaemia^1-3. The mechanism by which FVP induces this effect is not known although it has been shown that this induction does not result from the presence of erythropoietin (Ep) in the inoculum and is not dependent on the endogenous production of Ep (refs 1 and 3). As yet, no system for both infection in vitro and subsequent expression of erythroid differentiation in vitro has been described. We have developed a method whereby infection of spleen cells can be accomplished in vivo and the late events of erythroid differentiation can be studied in vitro. We report that spleen cells cultured soon after infection in vivo, before increases in haemoglobin synthesis are detectable, will later increase their rate of haem, or haemoglobin, synthesis in vitro. The effect of Ep on the FVP-induced erythroid differentiation was also tested.