Given that antibodies are made of protein, which membrane-enclosed cell organelle would you expect the plasma cells to have abundance of?

I believe the answer is rough endoplasmic reticulum.

Plasma cell secrete antibodies which made of protein, so they will need many protein to do their role. Membrane-enclosed cell organelle that has an important role in protein synthesis is rough endoplasmic reticulum. Having more endoplasmic reticulum will help plasma cell to synthesis more antibodies.

protist eukaryotes that are not plants, animals, or fungi ("misfits")