ABSTRACT: INTRODUCTION: To investigate the role of interferon-gamma (IFN-gamma) in the onset and severity of dacryoadenitis in the CD25 knockout (KO) mouse model of Sjogren Syndrome. METHODS: CD25/IFN-gamma double KO (gammaDKO) mice were created by crossbreeding CD25KO and IFN-gammaKO mice. Mice were used at 8, 12, and 16 weeks. Lacrimal gland (LG) infiltrating lymphocytes were characterized with flow cytometry. Tear epidermal growth factor (EGF) concentration was measured with enzyme-linked immunosorbent assay (ELISA). Quantitative polymerase chain reaction (PCR) evaluated T-cell-related cytokines in LGs. Serum autoantibodies against M3R in LG lysates were detected with Western blot. RESULTS: gammaDKO LG showed lower lymphocytic infiltration at 8 weeks than in the CD25KO parental strain ( 20% versus 60%, respectively), which increased to CD25KO levels at 16 weeks. Flow-cytometry analysis showed an increase in CD4+ and CD8+ T cells with aging in gammaDKO LG, similar to that in CD25KO. gammaDKO had lower levels of interleukin (IL)-17A, transforming growth-factor (TGF)-beta1, IL-21, and CCL20, and higher IL-1beta and IL-13 mRNA transcripts in the LG than in the parental CD25KO strain. Autoantibodies to M3R were observed in both strains and significantly increased with aging in both strains. CD25KO mice had very low tear EGF concentrations at all ages, whereas the ear EGF concentration in gammaDKO mice significantly decreased with aging and inversely correlated with the presence of M3R autoantibodies and the degree of LG CD4 and CD8+ T-cell infiltration. CONCLUSIONS: The deletion of IFN-gamma in the CD25KO mice strain delays glandular destruction and preserves glandular function. M3R autoantibodies increased with aging in both the gammaDKO and the CD25KO strains. The decrease in LG function in gammaDKO correlated with the degree of T-cell infiltration and the presence of M3R autoantibodies.