Cutting Edge: Identification of Marginal Reticular Cells as Phagocytes of Apoptotic B Cells in Germinal Centers

Germinal centers (GCs) in secondary lymphoid organs generate large numbers of apoptotic B cells that must be eliminated by phagocytes to prevent the development of autoimmune diseases. Although tingible body macrophages engulf apoptotic GC B cells, whether stromal cells are also involved in this process is unclear. In this study, we identified marginal reticular cells (MRCs) as novel nonprofessional phagocytes for the clearance of apoptotic GC B cells in the spleen. We used CD19 eGFP (CD19 cre Z/EG) mice, which express enhanced GFP (eGFP) under the control of CD19 cre expression, to track B cells in the GCs after immunization with NP-chicken γ globulin plus aluminum salt. We demonstrated that the MRC population, as determined by expression of podoplanin or Rankl , specifically showed an eGFP signal in the cytoplasm after immunization. These results suggest that MRCs contribute to the clearance of apoptotic B cells in GCs.