TNFAIP3 encodes an ubiquitin modifying enzyme, A20, required to limit NF-kB activity downstream of TLR and TNF receptors. We have recently identified a novel TT>A polymorphism ~25 kb downstream of TNFAIP3 as the best candidate polymorphism responsible for the association of TNFAIP3 with SLE (Adrianto, Wen, Templeton, et al. Nature Genetics, in press). Here we investigate the functional consequence of expression of the risk haplotype defined by the minor -/A allele at position chr6:138,271,732-733 in peripheral B cells isolated from subjects expressing one copy of the risk haplotype compared to controls. With IRB approval, blood samples from 11 paired risk and controls were collected through the Large Lupus Family Registry at OMRF. Resting B cells from risk samples had significantly less A20 expression compared to controls. CD40L stimulation significantly increased A20 expression in control samples but not risk samples. CD40L induced higher NF-kB p52 activation and induced significantly more CD86 expression in risk compared to control samples. Overall, these results confirm the risk haplotype defined by the TT>A polymorphism confers functional consequences of lower A20 expression, enhanced NF-kB signaling and increased cellular activation of primary B cells. Inappropriate B cell activation as a result of reduced TNFAIP3 expression in cells carrying the TT>A variant likely contributes to increased autoimmunity and SLE risk.