MZB1 co-precipitated with the ER multichaperone complex glucose-regulated protein 94 (GRP94)-binding immunoglobulin protein (BiP) in the mouse plasmacytoma cell line Ag8.653 that does not express immunoglobulins [6], so MZB1 may assist IgM assembly as a molecular chaperone. Here, MZB1 is linked to plasmacytoma.