MKI67 and nephritis: Since most classical plasmablasts continue to proliferate and thus are Ki-67+, the isotype-switched B cells exhibiting a CD19hi, CD138+, MHCII+ Ki-67− phenotype in our experiments may represent a B cell phase intermediate between a plasmablast and terminally differentiated plasma cells, such as the early differentiated CD138hi MHCII+ plasma cell phenotype previously documented in kidney inflammation and observed following sheep red blood cell immunization (80, 81).