The understanding of immune responses of the horse is essential for infectious disease research, vaccine development, and testing new treatments for acute and chronic inflammatory diseases. Immunological research requires specific antibodies, typically monoclonal antibodies (mAbs). MAbs to more than 250 different cell surface markers and over 60 cytokines/chemokines are available for humans or mice. For horses, the number of available mAbs to immune system molecules has grown in recent years due to NIFA-funded reagent development projects from about 30 to presently >60 mAbs. However, many immune reagents for horses are still lacking. The hypothesis of this proposal is that new mAbs will improve the evaluation of host immunity during infectious and inflammatory diseases of the horse. The project preceding this renewal proposal focused on mAbs to soluble immune markers such as cytokines/chemokines. The goals of this project are: Objective 1 - to finish the characterization and assay development for cytokine/chemokine mAbs, including generation of two additional mAbs and assays to improve the analysis of cell-mediated immunity and inflammation; Objective 2 – is the development of ten mAbs to cell surface molecules defined by equine researchers for an improved phenotypic characterization of major equine immune cell populations. A preliminary mAb priority list has been developed; Objective 3 - to further simplify the distribution of the mAbs and develop a sustainable access system for the equine immune reagents produced under the NIFA umbrella. We will continue to distribute high quality mAbs and provide validated immune marker assays to the entire equine research community.