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Erythrophagocytosis in vivo in sickle cell anemia
Abstract:
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.
Insights
Sickle red blood cells (RBCs) in patients with sickle cell anemia (SS) show increased in vivo erythrophagocytosis (Ep). This indicates significant membrane injury, validating in vitro findings and suggesting a role for cell senescence.
Area of Science:
- Hematology
- Cell Biology
- Pathophysiology
Background:
- Sickle red blood cells (RBCs) exhibit increased susceptibility to phagocytosis by macrophages in vitro.
- Erythrophagocytosis (Ep), the engulfment of RBCs by macrophages, is a key process in RBC clearance.
Purpose of the Study:
- To investigate the occurrence of in vivo erythrophagocytosis (Ep) in patients with sickle cell anemia (SS).
- To correlate Ep findings with clinical parameters and validate in vitro observations.
Main Methods:
- Examination of blood smears from 27 steady-state SS patients and controls.
- Differential white blood cell (WBC) counts to detect Ep.
- Comparison of hematocrit values between Ep-positive and Ep-negative SS patients.
Main Results:
- Ep was detected in 37% of SS patients (1-6/1,000 WBC or 1-10/100 monocytes).
- No Ep was observed in normal controls or splenectomized subjects.
- SS patients with Ep had significantly lower mean hematocrit values.
Conclusions:
- In vivo Ep occurs in a significant proportion of SS patients, indicating membrane injury of sickle RBCs.
- These findings support in vitro observations regarding sickle RBC phagocytosis.
- The mechanism of RBC senescence may contribute to the induction of Ep in sickle cell anemia.