CHARACTERIZATION OF B-CELLS EXPRESSING RECOMBINATION ACTIVATING GENESIN GERMINAL-CENTERS OF IMMUNIZED MOUSE LYMPH-NODES

Products of recombination activating genes (RAG-1 and RAG-2) involved in the rearrangement of Ig genes have been shown to be expressed only in immature stages of B cells. However, we have recently found that RA G genes were reexpressed in mature mouse B cells activated in vitro an d in germinal centers (GCs) of immunized mouse lymph nodes (LNs). Here , we report that RAG transcripts and their proteins were expressed in parallel with the formation of GCs in popliteal LNs from mice immunize d in the hind footpads. Immunocytochemical analysis revealed that RAG( +) B cells were localized within GCs and were present as apoptotic tin gible body cells. RAG expression is not considered a nonspecific resul t of apoptosis, since apoptotic B cells generated by surface Ig-engage ment did not express RAG genes. These results suggest a novel role of RAG products in the differentiation of B cells in GCs.