Haematopoiesis

Vitamin A deficiency appears to impair haematopoiesis of some lineages, such as CD4+ lymphocytes, NK cells and erythrocytes. In humans, vitamin A deficiency has been characterized by lower total lymphocyte counts and decreased CD4+ lymphocytes in peripheral blood; furthermore, CD4+ lymphocyte counts and/or percentage increased after vitamin A supplementation of deficient individuals (Semba et al., 1993a, b; Hussey et al., 1996). In the vitamin A-deficient rat, lower NK-cell, B-cell and CD4+ lymphocyte counts were found in peripheral blood, and these counts responded to retinoic acid supplementation (Zhao and Ross, 1995). Retinoids have been implicated in the maturation of pluripo-tent stem cells to cell lineages that produce different haematopoietic cell lines, such as lymphocytes, granulocytes and megakaryocytes. Retinoids also appear to play a role in the maturation of differentiation of pluripotent stem cells into multipotent colony-forming unit granulocyte-erythroid-macrophage mixed (CFU-GEMM) cells, and differentiation and commitment of CFU-GEMM into erythroid burst-forming units (BFU-E) and then into erythroid colony-forming units (CFU-E) (Perrin et al., 1997; Zermati et al., 2000).

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