The ATP‐gated P2X7 receptor (P2X7R) plays important roles in pro‐inflammatory responses. Recently, extracellular NAD has been shown to induce activation of P2X7R in murine T cells via ADP‐ribosylation involving an ADP‐ribosyltransferase ART2.2 that is constitutively expressed on murine T‐cell surfaces. We have recently reported that ART2.1, functionally and structurally similar to ART2.2, is markedly up‐regulated by pro‐inflammatory activation of murine macrophages which constitutively express high levels of the P2X7R. Here, we showed that extracellular NAD acts to covalently modify the P2X7R in both macrophages and T cells but with distinct functional consequences on the gating of channel activity. We monitored P2X7R channel activity by fura2‐Ca2+ influx assays and P2X7‐mediated pore formation by ethidium influx assays. Co‐expression of P2X7R with ART2.1 or ART2.2 in HEK293 cells verified that the P2X7R is a substrate for ART2.1, as well as ART2.2. In contrast with T cells, the ART2‐mediated ADP‐ribosylation of P2X7R in macrophages (or HEK293 cells) is not sufficient to gate the P2X7R. However, this allosteric modification of the macrophage P2X7R potentiates the ability of ATP to gate the channel as indicated by a left‐shift in the ATP dose‐response relationship. This supports a different role for extracellular NAD in the regulation of P2X7R‐dependent inflammatory responses of different cell types.