Re-engineering and functional analysis of a putative marker of self using phylogenetic variation
Ubiquitously expressed CD47 is reported to be a "marker of self" in mice, inhibiting phagocytic clearance of "self" cells by signaling through SIRPα on phagocytes. While receptor binding seems conserved in multiple species including human, conservation of function is not clear. We first demonstrate that SIRPα interactions with red cell CD47 is species-specific. However, adhesion assays indicate that physiological densities of these receptors do not predict stable interaction between red cells and phagocytes. We then exploit the observed phylogenetic divergence in human SIRPα interactions using CHO-cell display of CD47-GFP fusions and determine the species-specific SIRPα binding locus on CD47. Mouse to man divergence in CD47 mobility and lateral associations in red cells is then confirmed and shown to affect SIRPα interactions, with stronger interactions seen with mouse red cells. Soluble mouse SIRPαa binding to CHO-cell displayed CD47 is then used to show that the affinity in the mouse system is higher with possibly a different binding locus on CD47. Finally, it is shown that CD47-mediated phagocytosis inhibition observed with human phagocytes is weak, indicating quantitative differences in function between mouse and man.
Chemical engineering|Biomedical research|Molecular biology
Subramanian, Shyamsundar, "Re-engineering and functional analysis of a putative marker of self using phylogenetic variation" (2006). Dissertations available from ProQuest. AAI3225551.