SLC29A3 and Histiocytosis: As TLR7 and SCL29A3 are both localized to the endosomal compartments, SLC29A3 deficiency results in the accumulation of the TLR7 ligands, Guo, and dGuo, in TLR7-containing compartments, and thereby TLR7 activation drives histiocytosis in Slc29a3−/− mice.