B-cell deficiency and reduced B-cell reconstitution in hemoglobin-deficit mice

Objective To study the effect of persistent hemoglobin-deficit mutation (hbd/hbd) on hematopoiesis and the function of hematopoietic stem cells (HSCs). Methods Young and old mice homozygous for the spontaneous hbd/hbd mutation were compared to young and old wild-type control mice, all on the C57BL/6 background, over cellular composition in blood and bone marrow (BM) using cell counting, complete blood counts, and flow cytometry. BM cells from hbd/hbd mutants and normal controls were also tested for HSC engraftment in vivo using the competitive repopulation assay. Results Both young and old hbd/hbd mutants exhibited a microcytic anemia with significantly (p<0.01) lower levels of hemoglobin and mean corpuscular volume. There were significant declines in CD45R+ B cells in both blood (p<0.01) and BM (p<0.05) in old hbd/hbd mice, suggesting that B-cell homeostasis was compromised. Total BM cells per mouse was significantly increased (p<0.05) in old hbd/hbd mice. In the competitive repopulation assay in vivo, BM cells from old hbd/hbd donors showed slightly decreased contribution to T cells and myeloid cells but a significantly (p<0.01) decreased engraftment in B lymphocytes, indicating that B-cell hematopoiesis was compromised in old hbd/hbd mice. These data differ from results previously obtained from normal C57BL/6 mice in which BM cell engraftment ability does not decrease with donor age. Conclusion Persistent hbd/hbd mutation causes hematopoiesis defects in the B cell lineage.