MZB1 and plasmacytoma: First identified in plasmacytoma cell lines as an 18 kDa ER-localized protein, Mzb1 expression had been proposed to be specific for B and T lymphocytes in the spleen [5,6], yet microarray analysis of Mzb1 expression in different subpopulations of immune and non-immune cells revealed that Mzb1 is preferentially expressed in B cells and, to a lower extent, dendritic cells [148].