A new procedure for the quantitative assessment of p-glycoprotein efflux pump associated with human T lymphocytes

P-glycoprotein (P-gp), a multidrug transporter located in plasma membranes, reduces intracellular availability of some drugs. Upregulation of P-gp has been observed in some clinical situations, including chronic inflammatory disease and viral infection. However, P-gp is expressed in only a small subset of peripheral blood mononuclear cells (PBMC) and at much lower quantities than it is on P-gp-positive cell lines used in other studies.

P-gp expression was assessed by flow cytometry by using a commercially available, anti-P-gp, allophycocyanin-conjugated monoclonal antibody. Flow cytometry was also used to determine the efflux activity associated with P-gp; with this process, refluxed fluorescent P-gp substrate, rhodamine 123 (Rho123), was determined by the subsequently identified P-gp-positive PBMC subset. Use of verapamil during the dye-loading procedure maximized the amount of dye retained by the cells.

The use of allophycocyanin-conjugated monoclonal antibody allowed for the identification of P-gp-positive PBMC subsets, even when the cells were fully loaded with Rho123. We used a logical gating strategy to identify a P-gp-positive PBMC subset, after which P-gp efflux activity of the PBMC subset could be quantitatively assessed. This new procedure enabled us to assess the P-gp efflux function of T lymphocytes in some clinical situations, which induced P-gp upregulation in vivo.

This new procedure enables us to quantitatively assess the P-gp efflux activity associated with PBMC.