** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS (PRRSV) WAS FIRST DESCRIBED IN THE UNITED STATES IN 1987 AS AN INFECTIOUS AGENT RESPONSIBLE FOR A MYSTERY SWINE DISEASE. CLINICAL SIGNS AFTER INFECTION INCLUDE REPRODUCTIVE FAILURE DURING LATE GESTATIONSUCH AS ABORTIONS, RESPIRATORY DISTRESS IN YOUNG PIGS, AND POOR GROWTH PERFORMANCE.FURTHERMORE, PRRSV IS OFTEN COMPLICATED BY SECONDARY INFECTIONS THAT CAN LEAD TO A MUCH MORE SEVERE DISEASE AND INCREASED MORTALITY.PRRSV IS CURRENTLY ENDEMIC IN MOST SWINE-PRODUCING COUNTRIES AND IS THE MOST ECONOMICALLY DESTRUCTIVE VIRUS AFFECTING SWINE WORLDWIDE. VACCINES AND OTHER CONTROL MEASURES HAVE NOT PROVED EFFECTIVE IN DISEASE CONTROL AND ELIMINATION. PRRSV IS DIVIDED INTO TWO DISTINCT SPECIES, PRRSV-1 AND PRRSV-2.THE VIRUS MAINLY INFECTS PORCINE ALVEOLAR MACROPHAGES.PORCINE CD163 PROTEIN SERVES ASTHE MAJORCELLULAR ENTRY RECEPTOR FOR PRRSV. OUR PREVIOUS WORK SHOWED THAT GENETICALLY MODIFIED PIGS LACKING EXPRESSION OF CD163 ON MACROPHAGES ARE COMPLETELY RESISTANT TO INFECTION WITH PRRSV. SINCE CD163 IS CRITICAL FOR PRRSV INFECTION, THE GOAL OF THE PROPOSED PROJECT IS TO IDENTIFY SPECIFIC REGIONS AND DOMAINS IN CD163 IMPLICATED IN VIRAL INFECTION.THE FIRST OBJECTIVE IS THE USE OF A NOVEL IN VITRO SYSTEM TO MAP THE CD163 PEPTIDE SEQUENCES RECOGNIZED BY PRRSV-1 AND PRRSV-2 GENOTYPES. THE GOAL OF THIS OBJECTIVE IS TO GENERATE MODIFICATIONS IN CD163 THAT PREVENT PRRSV INFECTION WITHOUT AFFECTING KEY BIOLOGICAL FUNCTIONS OF THE VIRAL RECEPTOR.THE SECOND OBJECTIVE OF THE PROPOSED PROJECT IS TO IDENTIFYSPECIFIC REGIONS IN VIRAL PROTEINS AND CD163 INVOLVED IN VIRUS-RECEPTOR BINDING. UNDERSTANDING THE MOLECULAR BASIS FOR THE INTERACTION BETWEEN CD163 AND PRRSV CREATES THE OPPORTUNITY TO EXPLORE NOVEL CONTROL MEASURES, SUCH AS VACCINES THAT TARGET PUTATIVE NEUTRALIZING EPITOPES AND ANTIVIRAL DRUGS, WHICH CAN INTERRUPT THE INTERACTION.OUR FINDINGS WILL PROVIDE CRITICAL INFORMATION FOR UNDERSTANDING CD163-MEDIATED PRRSV INFECTION AND ENHANCE OUR COMPREHENSION OF VIRAL PATHOGENESIS. THE RESULTS OBTAINED FROM THIS PROPOSAL WILL BE INSTRUMENTAL FOR THE DEVELOPMENT OF NOVEL STRATEGIES TO PREVENT OR BLOCK PRRSV INFECTION AND WILL PROVIDE NEW DATA THAT CAN BE USED TO CONTROL INFECTION WITH NEW VACCINES AND SMALL MOLECULES THAT CAN DISRUPT THE VIRUS-CD163 INTERACTION. FURTHERMORE, OUR RESULTS WILL PROVIDE SIGNIFICANT INFORMATION TO DESIGN A NEW SET OF CD163 RECEPTORS THAT ARE RESISTANT TO PRRSV INFECTION BUT STRUCTURALLY AND FUNCTIONALLY INTACT.