Table 4.
Behavior of liposomes and RBC in the circulation.
| Features | Parameters | Liposomes | RBC |
|---|---|---|---|
| Circulation | Life span in blood | Minutes – Hours | 4 Months |
| Biocompatibility | Limited | Exceptionally high | |
| Distribution in blood | Plasma + Leukocytes | Cellular fraction (pellet) | |
| Access to tissues | Select tissues | Normally none | |
| Protection from clearance | Passive non-specific (PEG) | Active: DAF, CD59, CD47 | |
| Changes with time | Unknown, NSU | Starvation & senescence | |
| Clearance | Prevalent normal pathway | Variable, NSU | Phagocytosis |
| Tissues and compartments | RES, tissues & lymphatics | RES | |
| Clearing organ of RES | Liver | Spleen | |
| Mechanism of clearance | Uptake by phagocytes | Retention in follicles | |
| Recognition mechanisms | APC and other opsonins | Complement | |
| Opsonization pathways | Non-specific | Loss of DAF, CD47, sialic acid | |
| Rate | Fast | ??? | |
| Abnormalities | Premature senescence | Not known, NSU | Rigidification & fragility; congenital cytoskeletal protein defects; cytosolic enzymopathies |
| Vascular adhesion | Similar to above | SCD, sepsis, malaria | |
| Lysis | Similar to above | PNH, snake venom, circulating auto/alloantibodies | |
Abbreviations: NSU: not sufficiently understood, RES – reticuloendothelial system, PEG – polyethylene glycol, DAF – Decay Acceleration Factor, SCD – Sickle Cell Disease, PNH – paroxysmal nocturnal hematuria, APC – alternative pathway of complement.