To further investigate the role of various blood components in prion disease transmission, we intracranially inoculated genetically susceptible VRQ/ARQ and ARQ/ARQ sheep with inocula composed of CD11c+ B1 lymphocytes, CD68 +macrophages, or platelet-rich plasma derived from clinically ill sheep infected with the US no. 13–7 scrapie agent. This evidence concerns the gene ITGAX and scrapie.