Autoimmune uveitis is a major cause of blindness. It is thought to be caused by activated autoreactive T cells specific for sequestered retinal antigens. To understand the natural triggers that activate these T cells and endow them with the ability to cross the blood-retinal barrier, we developed a retina-specific TCR transgenic (R161H) mouse model of spontaneous uveitis. Elimination of gut commensals by oral broad-spectrum antibiotic treatment (ABX) or by rearing under germ-free conditions (GF) significantly attenuated uveitis and reduced Th17 cells in the gut lamina propria. R161H T cells were activated in the intestine of specific-pathogen-free (SPF) mice through their clonotypic TCR. Upon exposure to bacteria-rich intestinal content extracts from specific-pathogen-free (SPF), but not GF or ABX mice, retina-specific T cells upregulated activation markers and acquired the ability to induce uveitis in naïve wild type recipients. These data support a role for gut microbiota as a source of surrogate antigen for triggering retina-specific T cells, but do not identify a specific commensal or antigen mimic. To dissect the importance of antigenic signals vs innate “adjuvant” effects, we colonized GF mice with selected commensals. Colonization of GF-R161H mice with SPF flora restored full development of uveitis. In contrast, monocolonization with segmented filamentous bacteria (SFB) or Turicibacter strain H121 (T.H121) partially restored disease with only SFB reaching statistical significance over GF control. SFB, but not T.H121, monocolonization restored gut Th17-producing cells, indicating that it possesses “adjuvant” activity. However, intestinal content extract from neither could activate R161H T cells in culture, indicating that both lack “antigen” activity. We conclude that microbial-derived innate “adjuvant” and adaptive “antigen” components are both required to trigger full development of uveitis.