These data suggest that possible interaction of HLA-Bw4 with the inhibitory receptor KIR3DL1 may counteract the activating receptors of the B haplotype in patients with acute viral encephalitis and this issue is further confirmed by the significant association at multivariate analysis of the interaction between KIR 3DL1 and HLA-A-BW4 allele and encephalitis (Exp (β): 43.04; p = 0.009). This evidence concerns the gene KIR3DL1 and encephalitis.