Plasma cells are terminally differentiated, antibody-secreting cells that are required for both the immediate and long-term antibody response following antigen exposure. Plasma cells are large in size, non-proliferative, and express little or no surface immunoglobulins. They secrete large amounts of antibodies and are considered to be more mature than plasmablasts. Short-lived plasma cells typically arise in the red pulp of the spleen immediately after infection, whereas long-lived plasma cells arise weeks after antigen exposure and typically reside in specialized niches in the bone marrow. Both mouse and human plasma cells are commonly identified as CD19-Syndecan-1/CD138+ cells. Human plasma cells also express high levels of CD38, while mouse plasma cells also express Ly6k, Sca-1/Ly6, and CD98 and lose expression of B220/CD45 R. In addition, both mouse and human plasma cells lack expression of IgD, and express low levels of MHC class II, along with high levels of CD27, CXCR4, BCMA, and the transcription factors, XBP1, IRF4, and BLIMP1. BLIMP1 is a transcriptional repressor and the master transcriptional regulator required for the development of both short- and long-lived plasma cells. BLIMP1 down-regulates the expression of both Pax5 and Bcl-6, two transcription factors that are required for mature B cell function, and induces expression of the transcription factor, XBP-1, by relieving Pax5-mediated repression. XBP-1 plays a central role in the induction of the secretory phenotype characteristic of plasma cells.
Detection of Plasma Cells in Human Peripheral Blood Mononuclear Cells by Flow Cytometry. Plasma cells (CD3-/CD19low/CD20-/low/CD38high/BLIMP1+) in human peripheral blood mononuclear cells were detected by staining with (A) an Alexa Fluor® 405-conjugated Mouse Anti-Human CD3 epsilon Monoclonal Antibody (R&D Systems, Catalog # FAB100V) and an Alexa Fluor® 594-conjugated Mouse Anti-Human CD19 Monoclonal Antibody (R&D Systems, Catalog # FAB4867T). CD3-/CD19+ cells were gated. (B) Expression of CD20/MS4A1 and CD38 on cells in the CD3-/CD19+ gate was determined by staining with an APC-conjugated Mouse Anti-Human CD20/MS4A1 Monoclonal Antibody (R&D Systems, Catalog # FAB4225A) and a PerCP-conjugated Mouse Anti-Human CD38 Monoclonal Antibody (R&D Systems, Catalog # FAB2404C). CD20-/low/CD38+ cells were gated. (C) Expression of BLIMP1 in the CD20-/low/CD38+ cell population was determined by staining with a PerCP-conjugated Mouse Anti-Human CD38 Monoclonal Antibody (R&D Systems, Catalog # FAB2404C) and a PE-conjugated Mouse Anti-Human BLIMP1/PRDM1 Monoclonal Antibody (R&D Systems, Catalog # IC36081P).