TLR7 and Arthritis: Conversely, after arthritogenic serum transfer in K/BxN serum-induced arthritis, collagen-induced arthritis, and human TNF transgene insertion, only pDC deficient mice showed exacerbations of symptoms and signs of inflammatory arthritis [66] and topical imiquimod, a TLR7 agonist, increased pDC recruitment and activity which subsequently improved arthritis [66].