The overall effects of IL-17A produced by CNS resident cells seem to be localized [21] and not sufficient to induce depression, however it has been hypothesized that in some diseases, such as SpA, where the production of IL-17A is increased by a pathogenic sub-population of Th17 at tissue and enthesis level, making the stimulus working in promoting the onset of depressive symptoms [22]. The gene discussed is IL17A; the disease is major depressive disorder.