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Macrophage-inflammatory protein-1alpha receptor expression on normal and chronic myeloid leukemia CD34+ cells
S E Nicholls1, G Lucas, G J Graham
1Leukemia Research Fund Cellular Development Unit, University of Manchester Institute of Science and Technology (UMIST), Manchester, United Kingdom.
Abstract:
We have assessed expression of MIP-1alpha binding sites on the surface of CD34+ cells from normal bone marrow (NBM) and chronic myeloid leukemia (CML) peripheral blood. This study has highlighted a small subpopulation of CD34+ (15.7 +/- 6.2% in NBM and 9 +/- 4% in CML), which has specific macrophage-inflammatory protein-1alpha (MIP-1alpha) cell surface binding sites. Further phenotypic characterization of the receptor-bearing cells has shown that they do not express the Thy-1 Ag, suggesting that they are committed progenitor cells rather than CD34+ Thy+ stem cells. However, more than 80% of methanol-fixed CD34+ cells do bind MIP-1alpha, suggesting that these cells may possess a pool of internal receptors, although we were unable to induce cell surface expression by cytokine stimulation. The percentage of these CD34+, MIP-1alpha-R+ cells present in the CD34 compartment of NBM is significantly higher than in CML, implicating lack of binding sites as part of the mechanism for the loss of response to this chemokine seen in CML. Specific Ab to the MIP-1alpha receptor implicated in HIV infection, CCR5, revealed that very few CD34+ cells expressed these receptors and that expression was confined to the CD34+ Thy- progenitor population. Data presented in this work suggest that active binding sites for the stem cell growth inhibitor MIP-1alpha are not constitutively expressed on the surface of most resting primitive multipotent cells, and that these cells are not potential targets for HIV-1 infection through CCR5.
Insights
Normal bone marrow and chronic myeloid leukemia CD34+ cells show limited macrophage-inflammatory protein-1alpha (MIP-1alpha) surface binding sites. Reduced MIP-1alpha receptor expression on CML cells may explain their diminished response to this chemokine.
Area of Science:
- Hematology
- Immunology
- Cell Biology
Background:
- CD34+ cells are crucial hematopoietic stem and progenitor cells.
- Macrophage-inflammatory protein-1alpha (MIP-1alpha) is a chemokine involved in cell regulation.
- Chronic myeloid leukemia (CML) is characterized by aberrant cell proliferation.
Purpose of the Study:
- To investigate MIP-1alpha binding site expression on CD34+ cells from normal bone marrow (NBM) and CML.
- To determine the role of MIP-1alpha receptor expression in CML pathophysiology.
- To assess the potential of CD34+ cells as targets for HIV-1 infection via CCR5.
Main Methods:
- Flow cytometry was used to assess MIP-1alpha binding sites on CD34+ cells.
- Phenotypic characterization of receptor-bearing cells was performed using Thy-1 antigen.
- Antibodies against CCR5 were used to evaluate HIV-1 receptor expression.
Main Results:
- A small subpopulation of CD34+ cells in NBM and CML expressed MIP-1alpha surface binding sites.
- These receptor-bearing cells were identified as committed progenitors (Thy-1 negative).
- Significantly higher percentage of MIP-1alpha-R+ cells were found in NBM compared to CML, suggesting impaired chemokine response in CML.
- Very few CD34+ cells expressed CCR5, primarily on CD34+ Thy- progenitors.
Conclusions:
- MIP-1alpha binding sites are not constitutively expressed on most primitive multipotent stem cells.
- Reduced MIP-1alpha receptor expression on CML CD34+ cells may contribute to their altered response to this chemokine.
- Resting primitive multipotent cells are unlikely targets for HIV-1 infection through CCR5.