| Macrophages are professional phagocytes that are able to recognize non-self, such as foreign cells or particles from self cells based on the presence of CD47, a marker of self. CD47 is a broadly distributed cell-surface protein that is expressed in all species through its interaction with the signal regulatory protein alpha (SIRPalpha) found on macrophages, sending a self signal that ultimately prevents uptake. This self signal is a key attractive feature for engineering and designing long-circulating carriers by evading macrophages from a biological approach than the traditional physical methods. While this theory of a "marker of self" has been proposed in mice, the broad implications as a self signal in other species, such as humans have been received with skeptism. This dissertation work investigates the role of CD47 in humans through understanding the functional implications in macrophage signaling. A recombinant human CD47 was used to first establish the importance of the protein during phagocytic inhibition when attached to synthetic particles. The extracellular domain was used to correlate the essential function of CD47 with SIRPalpha. We found that CD47 signal self leading to the deactivation of myosin in macrophages. This species-specific self signal is dependent on the phosphorylation signal associated with SIRPalpha based on binding affinity to CD47 that determines the fate of the macrophage's target. Through the direct interaction of CD47 with SIRPalpha and the many polymorphisms in humans, we determined difference in affinity that may have potential implications for autoimmune diseases. In all, this work unravels the self marker CD47 in human as a critical and potent inhibition signal for potential applications in synthetic particles and viruses for usage as implants, drug delivery carriers or gene therapy. |
