Differential Response of CD34+Cells Isolated from Cord Blood and Bone Marrow to MIP‐1α and the Expression of MIP‐1α Receptors on These Immature Cells

Abstract

Macrophage inflammatory protein-1 alpha (MIP-1α) has been shown to have a role in the control of myeloid stem and progenitor cell proliferation. Recent evidence suggests that MIP-1α also has a stimulatory effect on proliferation of mature progenitors as well as an inhibitory effect on immature progenitors in vitro. We have compared the effect of MIP-1α on myeloid and erythroid colony formation of CD34⁺ cells isolated from bone marrow and cord blood. In the presence of MIP-1α, bone marrow granulocyte-macrophage-colony forming cells (GM-CFC) were inhibited over a dose range of 15 ng/ml to 500 ng/ml, and GM-CFC from cord blood CD34⁺ cells were stimulated over the same dose range. MIP-1α suppressed BFU-E colonies in both bone marrow and cord blood. Using thymidine suicide assays, the influence of MIP-1α on the cycling status of the cells was assessed. A good correlation between the effect of MIP-1α on colony formation and cell cycle progression was observed. These results suggest that there is a differential response to MIP-1α when bone marrow and cord blood CD34⁺ cells are compared. Using flow cytometry and a biotinylated human MIP-1α/avidin fluorescein conjugate, the expression of MIP-1α receptors on CD34⁺ cells was assessed. The data indicated that there was little quantitative difference in overall expression of receptors (82.9% versus 93%) from bone marrow or cord blood, respectively. However, when Northern blot analysis was used, mRNA for two different MIP-1α receptors CCR1 and CCR5 could be detected in bone marrow, but only CCR1 mRNA was seen in cord blood CD34⁺ samples. Therefore, the expression of different receptor subtypes on CD34⁺ cells may be responsible for the difference in MIP-1α responsiveness observed.