Macrophages are a prominent component of the effector cell compartment in a number of CD4+ T cell-mediated organ-specific autoimmune diseases. In this study, we investigated the role of the sialic acid binding Ig-like lectin sialoadhesin (Sn, Siglec-1) in a model of interphotoreceptor retinal binding protein peptide-induced experimental autoimmune uveoretinitis in mice with targeted deletion of Sn. Our data show that compared with wild-type mice, experimental autoimmune uveoretinitis is reduced in severity in the initial stages in the Sn knockout (KO) mice. In addition, there is a reduction in the proliferative capacity of T cells from the KO mice draining lymph nodes after immunization with interphotoreceptor retinal binding protein peptides, which is manifest some days before disease onset and persists for the duration of disease. Furthermore, activated T cells from the draining lymph nodes of Sn KO mice secrete lower levels of IFN-gamma. The data suggest a role for Sn in "fine tuning" the immune response to autoantigens by modulating T cell priming.