TCR gene rearrangement in the peripheral lymphoid organs

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We have established GFP (green fluorescence protein) gene knock-in Recombination activating gene-2 (RAG-2) -knockout animals to detect TCRαβgene rearrangement in the peripheral lymphoid organs. RAG-2 is essential for gene rearrangement of both antigen receptors of T and B cells. To identify T cell subpopulations undergoing TCR rearrangement in the peripheral lymphoid organs other than the thymus, we established mice in which a GFP gene is knocked in the RAG-2 gene locus (RAG2-GFP mice). In the thymus and bone marrow of RAG2-GFP mice, as expected, GFP expression was detected in appropriate stages of developing T cells and B cells. Interestingly, a fraction of Thyl.2^+ cells in the Peyer's Patch are found to be GFP-positive. The GFP-positive cells express high levels of surface TCRβ and CD3 on the surface, suggesting mature T cells with rearranged TCRαβ. However, significant levels of signal-end breaks of Jα and Dβ locus were detected by ligation-mediated PCR analysis. Moreover, circular DNAs generated from TCRα and TCRβ gene locus were detected at levels comparable to those of total thymocytes. These results suggest that there exist secondary rearrangement events of TCR α and β gene in a fraction of the Peyer's Patch T cells.