OA is the most common cause of disability in the United States, and evidence over the last several decades suggests that OA is not simply a “wear and tear” disease of articular cartilage. The majority of OA patients present with low-grade inflammation wherein inflammatory cytokines and chemokines released from cartilage and synovium home macrophages and CD4+ T cells to the joint in chronic OA, with no information available for early OA. The overall goal of this project was to investigate the opposing roles of immunosuppressive Regulatory T (Treg) cells and proinflammatory T Helper 17 (Th17) cells in early osteoarthritis (OA), and to identify potential timing and novel targets for immunotherapeutic intervention. It has previously been demonstrated that Tregs are enriched within the synovial membrane of patients with chronic OA, but their anti-inflammatory functions are suppressed, and Tregs are not able to restore joint homeostasis. The purpose of the first study was to determine if an enriched population of Tregs actively secreting anti-inflammatory IL-10 would be able to resolve inflammation induced by IL-1beta in an equine in vitro, co-culture model of OA. Results of this study determined that Tregs alone were unable to restore metabolic and catabolic imbalance but were able to do so in the presence of anti-IL-6 neutralizing antibody, and that it was significantly influence by the chondrocyte/synoviocyte and Treg donors. The results of this study demonstrate that IL-6 is a promising therapeutic target in early OA, that a personalized medicine approach will need to be taken anti-IL-6 immunotherapy. The purpose of the second study was to determine a timeline for infiltration of Tregs and Th17 cells into the synovial fluid during progression of posttraumatic OA (PTOA) using flow cytometry. This study utilized synovial fluid samples from horses with varying severity of naturally occurring PTOA and with healthy joints. The use of the horse was pivotal for this study, because control samples are typically not available from humans, and small animal models do not provide sufficient volumes of synovial fluid for analysis. The results of this study demonstrated, for the first time, plasticity of Tregs to a Th17-like Treg phenotype, with secretion of Th17 cytokine, within the joint during moderate PTOA, and that Tregs and Th17 cells are already present in the synovial fluid of healthy joints. Furthermore, Th17 cells were more populous in more severe disease compared to Tregs. This knowledge is critical to determine timing and targets of existing and approved immunotherapeutics that could be translated for the treatment of OA. These results warrant further studies to determine the driving factors for Treg phenotype plasticity and Th17 cell homing to and maintenance within the joint. The purpose of the third study was to identify pathways and proteins associated with persistent inflammation in early PTOA as potential therapeutic targets in the prevention of PTOA. Synovial fluid samples were collected from human patients at 1-week and 4-weeks post anterior cruciate ligament (ACL) reconstruction surgery and patients were stratified into two groups based on IL-6 concentration in synovial fluid at 4-weeks post-ACL reconstruction as those who were non-responders (>316 pg/mL IL-6) to surgery and those who were responders (<316 pg/mL IL-6). Samples were analyzed using liquid chromatography-mass spectrophotometry. The results of this study indicated that those who are non-responders to ACL reconstruction have a high abundance of proteins related to the complement pathway and release of primary, azurophilic granules by neutrophils into synovial fluid. This demonstrates that non-responders to ACL reconstruction can be identified by IL-6 concentrations in synovial fluid and reveals novel targets for immunotherapeutic intervention in the prevention of PTOA following ACL reconstruction.