R-phycoerythrin-conjugated antibodies are inappropriate for intracellular staining of murine plasma cells.

Phycoerythrin (PE) is a type of phycobiliproteins found in cyanobacteria and red algae. PE-conjugated antibodies are broadly used for flow cytometry and immunofluorescence microscopy. Because nonspecific binding of antibodies results in decreased analytic accuracy, numerous efforts have been made to unveil cases and mechanisms of nonspecific bindings. However, nonspecific binding of specific cell types by a fluorescent dye-conjugated form of antibody has been rarely reported. In the present study, we discovered that PE-conjugated antibodies, but not FITC- or APC-antibodies, selectively stained lamina propria plasma cells (LP-PCs) from the murine small intestine after membrane permeabilization. We demonstrated that LP-PC-selective staining with PE-antibodies was not due to interactions of antibody-epitope or antibody-Fc receptor. This unexpected staining by PE-antibody was not dependent on the mouse strain of LP-PCs, experimental methods, or origin species of the antibody, but dependent on PE itself. This phenomenon was also observed in plasma cells isolated from bone marrow, spleen, and mesenteric lymph nodes. Furthermore, in vitro activated B cells and in vivo generated LP-PCs were also selectively stained by PE-conjugated antibodies. Taken together, these results show that PE-conjugated antibodies are inappropriate for intracellular staining of murine plasma cells.