Recombination-activating gene (RAG) 1 and 2 are essential for the gene rearrangement of antigen receptors of both T and B cells. To investigate RAG gene expression in peripheral lymphoid organs other than the thymus and bone marrow, we established mice in which a green fluorescent protein (GFP) gene is knocked-in the RAG2 gene locus (RAG2-GFP mice). In the thymus and bone marrow of heterozygous RAG2-GFP mice, as expected, GFP expression was detected in the appropriate stages of developing T and B cells. Interestingly, only a fraction of Thy-1.2+ cells in the Peyer's patch were found to be GFP+ amongst the peripheral lymphoid organs. The GFP+ cells expressed high levels of surface TCRβ and CD3, suggesting mature T cells with rearranged TCRαβ. However, they showed activated/memory phenotypes, i.e. CD45RBlow, CD69high, CD44high and CD62Llow, and belonged to a CD4+CD8+ population expressing c-kit, IL-7R and pTα characteristic of immature developing lymphocytes. Moreover, RAG+ Peyer's patch T cells seem to be of thymic origin as judged by their expression of CD8αβ. These results show that there exists a fraction of mature T cells expressing RAG genes in the Peyer's patch, implying a potential for a secondary rearrangement of TCR in extrathymic tissues.
All Science Journal Classification (ASJC) codes
- Immunology and Allergy