Erythrophagocytosis in vivo in sickle cell anemia.

Recent observations that the sickle RBC are excessively susceptible to phagocytosis by macrophages in vitro prompted me to look for evidence of in vivo erythrophagocytosis (Ep) in patients with sickle cell anemia (SS). Freshly prepared smears of unmanipulated blood of 27 patients with SS in steady state were examined for Ep by a 500-cell differential white blood cell (WBC) count performed in duplicate. Ten of 27 (37%) SS patients showed Ep (1-6/1,000 WBC or 1-10/100 monocytes). By contrast, no Ep was found in similarly prepared blood smears of 25 normal adult controls and nine splenectomized subjects. The mean hemotocrit value of the Ep(+) SS patients was significantly lower than that of the Ep(-) patients (21.0 +/- 1.7% vs 24.0 +/- 2.7% p less than 0.01). Considering the rarity of spontaneous Ep in unmanipulated blood from normal subjects and the relative insensitivity of the method used, the finding of Ep in over one third of SS patients indicates a significant membrane injury of the sickle RBC and serves to validate the in vitro observations. The possible role of the "senescence" mechanism in the induction of Ep is discussed.