Specific and non-specific phagocytosis of ligand-grafted PLGA microspheres by macrophages

Area of Science:

• Biomaterials Science
• Cell Biology
• Nanotechnology

Background:

• Poly(d,l-lactide-co-glycolide) (PLG) microparticles are utilized in drug delivery.
• Alveolar macrophages play a crucial role in lung immunity and particle clearance.
• Surface modification of microparticles can influence their interaction with immune cells.

Purpose of the Study:

• To investigate the impact of covalently grafted ligands on the uptake of PLG microparticles by alveolar macrophages.
• To elucidate the mechanisms underlying ligand-mediated microparticle uptake.
• To determine how surface charge and ligand type affect phagocytosis.

Main Methods:

• PLG microparticles (2.5 µm) prepared via spray drying.
• Surface functionalization with wheat germ agglutinin (WGA), RGD peptide, mannose-PEG(3)-NH(2), and poly-L-lysine (PLL) using carbodiimide chemistry.
• Quantification of grafting efficiency and surface charge (zeta potential).
• Confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) for characterization.
• Macrophage uptake studies using CLSM, including experiments with free ligand, cytochalasin D, and temperature variations.

Main Results:

• Ligand-grafted microparticles exhibited 2-4 times higher uptake compared to ungrafted particles.
• Negatively charged ligand-grafted particles showed saturable uptake, unlike cationic PLL-grafted particles.
• Evidence suggests a specific, receptor-mediated phagocytosis mechanism, inhibited by free ligand, cytochalasin D, and low temperatures.
• The balance between specific and non-specific uptake varied with ligand type and particle-to-cell ratio.

Conclusions:

• Covalent ligand grafting is an effective strategy to enhance microparticle uptake by alveolar macrophages.
• The enhanced uptake is mediated by specific receptor-ligand interactions, suggesting targeted delivery potential.
• Understanding the interplay between ligand type, surface charge, and uptake mechanisms is crucial for designing effective microparticle-based therapeutics.