Equine PBL transfer into NSG hosts. (A) Donor horse peripheral blood lymphocyte populations post-gradient centrifugation separation and prior to engraftment. (B–D) Percentages of equine CD4+, CD8+, CD21+ lymphocyte populations, respectively, in the peripheral blood of mouse recipients at day 7, 14, and 28 post-engraftment. (E) Percentages of equine CD4+, CD8+, CD21+ lymphocyte populations in the spleens of mouse recipients at 28 days post-engraftment. Splenic cells from the remaining 3 mouse hosts were cultured for 12 hours in the presence of PMA and ionomycin. Interferon gamma positive cells were assessed and compared with unstimulated cells (F).