Abstract Inflammatory arthritis (IA) is a common inflammatory joint-destructive condition that affects millions of individuals worldwide. Increased immune dysfunction and bone loss have been observed both in IA affected humans and in animal models. Proinflammatory events responsible for RA pathogenesis have been studied in detail; however, the protective mechanism remains under-explored. Earlier, we reported that 14-3-3zeta (z) is a molecular determinant of skewing T cell polarization and interleukin-17A (IL-17A) signal transduction. Here we demonstrate that 14-3-3z is an endogenous suppressor of IA. Loss of 14-3-3z in a novel CRISPR/Cas9 edited knockout (KO) rat resulted in early-onset and severe arthritis in animal models of inflammatory arthritis. Arthritic 14-3-3z KO animals showed increased bone loss and immune cell infiltration in synovial joints. Rescue experiments to supplement the 14-3-3z by immunization during the pre-symptomatic phase resulted in significant arthritis suppression in both wild-type and 14-3-3z KO rats. Immunization generated a robust increase in 14-3-3z antibody and IL-17A, suppressed several cytokines, including IFN-g, TNF-a, and Cxcl-1, preserved tissue mineral bone density, and trabecular bone volume. Our findings, taken together with the prior report of the molecular function of 14-3-3z as an antigen, indicate that antigenic 14-3-3z is responsible for a previously unrecognized inflammatory arthritis-suppressive mechanism.