Figure 5.

Active targeting ligands recognize cellular markers and facilitate internalization. The ability to differentiate between macrophage phenotypes can improve therapy specificity and reduce off-target effects. However, specific macrophage targeting is still limited by variable surface expression, significant overlap of expression between macrophage phenotypes, and a lack of understanding of macrophage phenotype and function. Currently, antibodies, peptides, carbohydrates, and aptamers are used to increase accumulation in specific macrophage populations. The decision of which ligand to use is a balance between biological considerations (target affinity, specificity, stability, and penetration) and chemical considerations (ease of modification and cost).