@Michael_B, I see the point being made here. However, for the purposes of the level at which the MCAT is testing the material my instinct is that denoting APC’s as specialized is perfectly reasonable.
My thought process is “what are they specialized relative to?” Given the context, seems like it’s pointing to MHC-II glycoproteins being present on a narrower selection of cells. It’s honestly pretty minor but my only thing is that it might make it seem like there are APCs and then “specialized APCs” when the adjective “specialized” is only relative to how it’s more narrow than “all nucleated cells”