Reactive Arthritis, also known as postdysenteric arthropathy, is related to spondyloarthropathy 1 and chlamydia. An important gene associated with Reactive Arthritis is HLA-B (Major Histocompatibility Complex, Class I, B), and among its related pathways/superpathways are Innate Immune System and Response to elevated platelet cytosolic Ca2+. The drugs Azithromycin and Doxycycline have been mentioned in the context of this disorder. Affiliated tissues include bone and t cells, and related phenotypes are arthritis and joint stiffness