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A P2rx7 passenger mutation affects the vitality and function of immune cells in P2X4ko and other transgenic mice

Among laboratory mouse strains many genes are differentially expressed in the same cell population. As consequence, gene targeting in 129-derived embryonic stem cells (ESCs) and backcrossing the modified mice onto the C57BL/6 (B6) background can introduce passenger mutations in the close proximity of the targeted gene. Here, we demonstrate that several 129-originating transgenic mice in which P2rx7-neighboring genes were targeted carry a P2rx7 passenger mutation that affects the vitality and function of T cells. By the example of P2rx4tm1Rass we demonstrate that CD4+ and CD8+ T cells derived from these mice express higher levels of P2X7 when compared to corresponding cell populations in B6-WT mice. The increased T cell sensitivity towards the P2X7 activators adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD+) rendered these cells more vulnerable towards NAD-induced cell death (NICD) compared to their B6-WT counterparts. The enhanced NICD sensitivity significantly affected the outcome of functional assays e.g. cytokine production and cell migration. For P2rx4tm1Rass, we demonstrate that the expression of P2X7 is diminished in several innate immune cell populations, possibly as a side effect of P2rx4 targeting, and independent of the P2rx7 passenger mutation. These results need to be considered when working with P2rx4tm1Rass mice or other 129-based transgenic strains that target P2rx7 neighboring genes and might have implications for other mouse models.