And Recombination Competent

As Mtv-8+ V p5 Tg mice age, they accumulate Vp5low cells within the CD4+ T cell compartment, and it appears to be these cells that are undergoing TCR revision. Vp5low cells are CD44high, CD62Llow, both markers consistent with an activated T cell phenotype (Table E2.1). However, unlike antigen-activated lymphocytes, Vp5low cells are Thy-1low (our unpublished observations) and express both RAG1 and RAG2.20 The presence of recombination intermediates within the TCRp and p loci in these unusual cells indicates both that the RAG1 and RAG2 gene products are functional and that the TCR loci accessible to the recombinase.20 To more easily focus only on T cells undergoing TCR revision, the Vp5 transgene has been crossed onto a line of mice Tg for green fluorescent protein (GFP) under the control of the RAG2 promoter.22 Cells from these mice glow green when RAG2 is expressed. GFP+CD4+Vp5low peripheral T cells from these Mtv-8+ RAG reporter mice are larger than their GFP_Vp5high counterparts and are CD45RBhigh (our unpublished observations), both markers of acutely activated rather than memory

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