P2X7, an ionotropic receptor for extracellular ATP is expressed on immune cells including
macrophages, dendritic cells and lymphocytes and is up-regulated on non-immune cells following
injury. P2X7 is important in many biological processes including production of pro-inflammatory
cytokines and both cell proliferation and death. Previous work by our laboratory and others has
identified a potential role for P2X7 in the pathogenesis of glomerulonephritis (GN). However,
studies of auto-immunity have generated conflicting results and existing lines of P2X7 knockout
(KO) mice are incomplete with persistent splice variants. The aims of my project were to determine
a role for P2X7 in the pathogenesis of GN and vasculitis and to investigate its importance at a
cellular level in inflammatory responses of neutrophils and monocytes.
My project includes the first description of a novel P2X7 knockout rat showing that it is a true
knockout with no functional P2X7 protein expressed. Using bone marrow derived cells from the
knockout rat I show that different cell types have a differential requirement for P2X7 to cleave
active IL-1β, with dendritic cells but not macrophages able to cleave IL-1β via an ATP/P2X7
independent pathway in response to stimulation with LPS alone. I have also investigated the effect
of P2X7 KO on 3 different experimental models of glomerulonephritis and vasculitis and show that
P2X7 KO rats are not protected from disease severity or the generation of autoimmunity. I next
used a small molecule P2X7 antagonist in one of these models, nephrotoxic nephritis, showing that
it protected both wild type and P2X7 KO rats from disease, suggesting it may be mediating its
actions via off target effects.
I also investigated the potential role for P2X7 in human anti-neutrophil cytoplasm antibody
(ANCA) associated vasculitis (AAV). I show that human neutrophils express functional P2X7 on
the cell surface; this is a particularly interesting finding as this is a controversial area with
previously conflicting results. P2X7 is up-regulated on neutrophils and peripheral blood
mononuclear cells (PBMC) in patients with active AAV compared to patients in remission or
healthy controls. Neutrophils and PBMC can produce IL-1β in response to stimulation with MPO-
3
ANCA IgG and ATP. In patients with active AAV, P2X7 mRNA is present on infiltrating
leucocytes in the glomeruli and interstitium in renal biopsy tissue.
My data suggest that P2X7 is not a critical pathway in mediating glomerulonephritis and it is likely
that the antagonist is acting via one or more off target effects. Further understanding of these
mechanisms may lead to the identification of novel therapeutic targets and increase our
understanding of the pathogenesis of glomerulonephritis and vasculitis.