Interestingly, refractoriness of brain-derived microvascular endothelium to secrete chemokines in response to infection was also revealed despite evidence for the activation of NF-κB and p38 upstream signalling mechanisms and reduced ability of microvascular ECs to induce COX-2 expression and, consequently, secretion of PGE2 in response to R. rickettsii infection. This evidence concerns the gene NFKB1 and infection.