IL1R1 and anemia: In particular, none of the characteristic myeloid cell expansion, B cell loss, and anemia were observed in the blood of old Il1r1-/- mice, and despite persistence of an expanded HSC compartment, we found an attenuation of MPP3 expansion with diminished myeloid cell production and limited loss of erythrocyte progenitors in old Il1r1-/- BM (Fig. 7c).