Immune landscape in liver of neonatal mice with phlebotomy-induced anemia.

Background: Severe anemia is a common comorbidity in preterm infants in the neonatal intensive care unit, which is caused by phlebotomy, low erythropoietin levels, low red blood cell (RBC) lifespan, and exacerbated by the underlying erythropoietic immaturity. Anemia causes tissue hypoxia, which may alter the hematopoiesis niche in the liver. This study utilized our preclinical mouse model of phlebotomy-induced anemia (PIA) to investigate the immune cell atlas in the liver.

Methods: C57BL/6 mice were subjected to timed phlebotomy between postnatal days 2-10 to induce severe anemia. Immune cells in anemic liver were characterized by Single-cell (sc) RNA-sequencing and a flow cytometry approach.

Results: The scRNA-seq analysis revealed that PIA is associated with an altered immune landscape of the neonatal murine liver. We identified increased numbers of Ly6C2⁺monocytes and Gypa⁺erythroid cells and decreased numbers of lymphocytes (CD20⁺ [MS4a1]-B cells and Tcells) in the anemic liver. Further analysis of monocytes revealed a pro-inflammatory and highly chemotactic phenotype, while erythroid cells displayed a downregulation of inflammatory markers and maturational deficits. Lymphocytes (B and T cells) exhibited suppressed lipid metabolism processes, including those of steroids and hormones.

Conclusion: PIA in neonatal mouse pups is associated with myelopoiesis (specifically monopoiesis) and erythropoiesis while suppressing lymphopoiesis in the liver.

Impact: Anemia is nearly universal in preterm infants and is associated with increased morbidity and mortality worldwide, investigation of immune cell response in settings of preclinical anemia may be an index of therapeutic targets to modulate the response in anemia-related comorbidity. Our findings showed that phlebotomy-induced anemia in murine pup alters liver hematopoiesis including myelopoiesis and stressed erythropoiesis with suppressed lymphopoiesis. This study sheds light on emergency myelopoiesis, stressed erythropoiesis, and deficiency of lymphocytes in anemic liver, which may provide novel insight into the development of therapeutics to treat anemia in preterm infants and neonates.