As far as I understand, in complement system C3b gets deposited on pathogen surface but it can also be deposited on host cells. Host cells have some negative regulatory system such as membrane cofactor of proteolysis MCP, decay associating factor DAF etc which either removes C3b or cleave it using factor I to iC3b which can not form a C3 convertase or C5 convertase so no production of membrane attack complex on host cells.
However, phagocytes contain complement receptors CR2, CR3 etc that specifically recognise iC3b and engulfs the cells bearing it. While it is very useful for pathogens bearing iC3b (In those cases where pathogens contain sialic acid residue which attracts factor I and prevents forming MAC on those pathogens) wouldn't it be very dangerous for host cells?
So if there is receptors against iC3b on phagocytes then what is the point of host cells converting C3b into iC3b, they get killed one way or another anyway