P-glycoprotein expression and function in circulating blood cells from normal volunteers

Area of Science:

• Biochemistry
• Cell Biology
• Immunology

Background:

• The physiological role of P-glycoprotein (P-gly) in normal cells remains unclear, despite its established function in neoplastic cells.
• Identifying P-gly in blood and bone marrow suggests a potential role in hematopoietic development and function.

Purpose of the Study:

• To quantify the expression and function of P-glycoprotein (P-gly) and MDR1 gene expression in normal leukocytes.
• To determine the lineage-specific distribution and functional activity of P-gly in different leukocyte populations.

Main Methods:

• Flow cytometry and immunoblot analysis were used to detect P-gly on the cell surface of various leukocyte lineages (T-helper, T-suppressor, monocyte, granulocyte, B-lymphocyte, NK cell).
• Quantitative reverse transcription-polymerase chain reaction (RT-PCR) was employed to analyze MDR1 mRNA levels in purified leukocyte lineages.
• P-gly function was assessed using rhodamine 123 as a substrate in dual-labeling assays.

Main Results:

• MDR1 mRNA expression varied significantly across leukocyte lineages, with CD56+ cells (NK cells) showing the highest levels, followed by CD8+ T cells.
• P-gly surface expression and function generally correlated with mRNA levels, except in granulocytes (CD15+ cells).
• Granulocytes exhibited moderate MDR1 mRNA but lacked detectable surface P-gly and rhodamine 123 efflux, despite P-gly presence on immunoblots.

Conclusions:

• P-glycoprotein and MDR1 mRNA are expressed in normal leukocytes in a lineage-specific manner.
• CD56+ cells demonstrate the highest levels of P-gly expression and function among normal leukocytes.
• Granulocytes express P-gly, but this expression is not associated with the transport of the P-gly substrate rhodamine 123.