A20-deficient microglia and CD8 T cells in the brain

Tumor necrosis factor alpha induced protein 3 (TNFAIP3), also known as A20, is a key negative regulator of the canonical NFkB pathway, and acts at various levels of the signaling cascade downstream of receptor stimulation, thereby regulating the pro-inflammatory response. As such, its absence leads to the development of spontaneous inflammation; indeed, a number of SNPs in the A20 gene have been associated with various autoimmune diseases. Cell-specific deletion of A20 in mice can also lead to the development of spontaneous disease. Mice lacking A20 in their astrocytes have stronger disease in a model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Furthermore, A20 ko mice demonstrate spontaneous neuroinflammation, attributed to A20 deletion in either endothelial cells or microglia, the resident immune cells of the brain and spinal cord. We chose to examine the role of microglial A20 expression in the context of neuroinflammation by crossing A20 fl/fl to CX 3 CR1-Cre ERT2 mice. The resulting A20 fl/fl CX 3 CR1-Cre ERT2 (A20 Δmg ) mice were injected with tamoxifen to induce A20 deletion. Without A20, microglia spontaneously upregulate a number of NFkB target genes and have an activated morphology accompanied by an increase in GFAP + astrocytes in the cortex. Surprisingly, we found significantly more T cells (mainly CD8) infiltrate the brain and spinal cords of naive A20 Δmg mice relative to controls, after A20 deletion. Furthermore, upon EAE induction, A20 Δmg mice develop symptoms sooner than controls, and have stronger disease. Overall, the deletion of A20 in microglia leads to a spontaneous activation, which may enhance the susceptibility of these animals to developing neuroinflammation under specific condtions.