library_construction_protocol: A total of five birds from the MD-susceptible (ADOL 7 2) line were placed into a Horsfall-Bauer (HB) unit at hatch. At twelve days of age, they were sacrificed. After euthanizing the birds, the spleens were aseptically removed, homogenized, filtered to single-cell suspension through 35 micron cell strainers (Falcon, Inc), enriched for mononuclear leukocytes over Histopaque-1077 and transferred the same day on ice for single-cell capture and library preparation of a targeted 3,000 cells/sample. Single cell capture and cDNA library preparation were performed on the 10x Genomics Chromium Single Cell 3' instrument (10x Genomics, Pleasanton, CA) along with the 10x Chromium Single Cell 3' Reagent Kits v2 (Catalog number: PN-120237) according to the manufacturer's recommendations.