Table 1.
Models and techniques to address macrophage phenotype and function
| Models/Techniques | Examples | |
|---|---|---|
| Macrophage origin | Bone marrow transplantation | UBC-GFP into C57BL/6 mouse |
| Parabiosis | CD45.1 with CD45.2 mouse | |
| Adoptive transfer of progenitors | Fluorescent-labeled HSPCs or monocytes | |
| (Inducible) Cre-lox mouse | Cx3cr1CreER, Flt3Cre, Runx1CreER, crossed to loxP-flanked stop tdTomato or YFP | |
| Macrophage imaging and detection | Fluorescent reporter mice | Cx3cr1GFP/+, Csf1r-EGFP, hCD68-GFP |
| Antibodies | Fluorescent/radioisotope-labeled (microscopy, flow cytometry, PET, scintillation counting) | |
| Nanoparticles and liposomes | Gadolinium-based (MRI), iron oxide core (MRI), 18F and 89Zr label (PET) | |
| Macrophage depletion | Liposomes | Encapsulated bisphosphonates (e.g., clodronate) |
| (Inducible) (Cre) mouse models | CD11bDTR, Csf1rCreER:iDTR, Cx3cr1CreER:iDTR, CD169DTR, MaFIA | |
| Macrophage isolation and culture | Isolation by magnetic beads and/or FACS | CD11b+ F4/80+ tissue-resident macrophages |
| Bone marrow-derived macrophages | Culture with M-CSF | |
| Macrophage function | Imaging agents | MMPSense (MMP activity), ProSense (pan-cathepsin activity), fluorescent-labeled latex beads or dextran, pHrodo particle labeling, fluorescent bacteria |
| Cytokine responses | In vitro stimulation followed by ELISA, qPCR | |
| Metabolism | BioProfile FLEX analyzer, Seahorse XF analyzer | |
| Macrophage targeting and modulation | Cre-lox mouse models | Inducible Cre (e.g., Cx3cr1CreER, Csf1rCre) crossed to mouse with loxP-flanked gene of interest |
| Nanoparticles and liposomes | siRNAs, drugs | |
| (Ant)agonistic antibodies | anti-CD40, anti-CD47, anti-IL-1β, anti-IL-4 | |
| Small molecule inhibitors | Receptor tyrosine kinase inhibitor of Csf1r (PLX3397), inhibitor of CD40-TRAF6 interaction (TRAF-STOP) |
A caveat with current models and techniques is that they are never truly specific. For example, CD11b is expressed on all myeloid cells and some dendritic cells; and Cx3cr1 and Csf1r are also expressed on some dendritic cell subsets. LysM and Csf1r also target granulocytes. PLX3397 also inhibits, although with lower affinity, kit and Flt3. There are currently no strategies to exclusively target tissue-resident macrophages in a specific cardiovascular organ. DTR, diphtheria toxin receptor; ELISA, enzyme-linked immunosorbent assay; FACS, fluorescence-activated cell sorting; GFP, green fluorescent protein; HSPCs, hematopoietic stem and progenitor cells; MaFIA, macrophage Fas-induced apoptosis; M-CSF, macrophage-colony-stimulating factor; MMP, matrix metalloproteinases; MRI, magnetic resonance imaging; PET, positron emission tomography; TLR, Toll-like receptor; TRAF, tumor necrosis factor receptor-associated factor; UBC, ubiquitin.