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Updated: Mar 17, 2026
An In vitro Model to Study Heterogeneity of Human Macrophage Differentiation and Polarization
Published on: June 12, 2013
Alterations in P-Glycoprotein Expression and Function Between Macrophage Subsets
Theodore J Cory1, Hui He2, Lee C Winchester3
1Department of Clinical Pharmacy, University of Tennessee Health Science Center College of Pharmacy, Memphis, Tennessee, 38163, USA. tcory1@uthsc.edu.
Purpose:
Macrophages are an important cellular reservoir in HIV, and exist in two phenotypically dissimilar subsets, the pro-inflammatory M1 phenotype, and the anti-inflammatory M2 phenotype. The role of these two subsets is uncertain. We hypothesized that differences in drug efflux transporters exist between the subsets, which would result in altered intracellular drug concentrations between these cells.
Methods:
U937 monocytic cells were polarized to the M1 or M2 phenotype via treatment with interferon-gamma and LPS, or interleukins 4, 13, and LPS, respectively. PGP function was assessed with Hoechst 33342, and expression via western blotting. Intracellular lopinavir was assessed via LC-MS/MS. Data was confirmed with primary monocyte derived macrophages.
Results:
We observed significant differences in intracellular concentrations of lopinavir, a PGP substrate, with higher concentrations in M1 cells. PGP function and expression was higher in the M2 macrophages. These results were confirmed with primary monocyte derived macrophages.
Conclusions:
This data shows that there are previously unreported differences in P-glycoprotein expression between macrophage subsets, and suggests that there may be differences for other transporters. These differences can play a role in intracellular drug concentrations in these cells, and may allow for low-level HIV replication.
Insights
HIV drug concentrations differ between M1 and M2 macrophages due to P-glycoprotein (PGP) variations. M1 cells show higher intracellular lopinavir, while M2 macrophages exhibit greater PGP function and expression, impacting HIV persistence.
Area of Science:
- Immunology
- Pharmacology
- Virology
Background:
- Macrophages are key reservoirs for HIV.
- Two main macrophage subsets exist: pro-inflammatory M1 and anti-inflammatory M2.
- The distinct roles of M1 and M2 macrophages in HIV pathogenesis are not fully understood.
Purpose of the Study:
- To investigate differences in drug efflux transporter expression between M1 and M2 macrophage subsets.
- To determine if these differences affect intracellular drug concentrations, specifically for HIV medications.
Main Methods:
- U937 monocytic cells were differentiated into M1 or M2 phenotypes.
- P-glycoprotein (PGP) function was measured using Hoechst 33342.
- PGP expression was analyzed by western blotting.
- Intracellular lopinavir concentrations were quantified using LC-MS/MS.
- Experiments were validated using primary human monocyte-derived macrophages.
Main Results:
- M1 macrophages had significantly higher intracellular concentrations of lopinavir, an antiretroviral drug.
- M2 macrophages demonstrated increased PGP function and expression compared to M1 cells.
- These findings were consistent in both cell lines and primary macrophages.
Conclusions:
- Significant differences in P-glycoprotein expression exist between M1 and M2 macrophages.
- These transporter differences can alter intracellular antiretroviral drug concentrations.
- Variations in drug concentrations may contribute to persistent low-level HIV replication in macrophages.
