A STUDY ON THE ENGRAFTMENT AND TRAFFICKING OF BOVINE PERIPHERAL-BLOOD LEUKOCYTES IN SEVERE COMBINED IMMUNODEFICIENT MICE

Bovine lymphoid cells were engrafted into untreated and into sublethally irradiated scid/scid mice, following intraperitoneal (i.p.) injection of bovine peripheral blood leukocytes (PBL). To distinguish bovine from murine cells, bovine PBL were stained prior to i.p. injection with a fluorescent cell linker compound, PKH26-GL and, after cell recovery, labelled with a monoclonal antibody (mAb) reactive with the bovine pan leukocyte cell surface marker, CD45, and analyzed by flow cytometry. This dual labelling system was used to monitor tissue localization and migration of bovine cells within PBL-SCID-bo from 30 min to 64 days after bovine PBL injection. Inoculated bovine PBL were rapidly cleared from the peritoneal cavity of PBL-SCID-bo over the first 24 h after injection, then bovine cell numbers within the peritoneal cavity increased gradually over the next 35 days. No bovine cells were observed in the peritoneal wash from either non-irradiated or irradiated mice after Day 56. Bovine cells were detected in the spleens of both non-irradiated and irradiated mice 12-14 days after inoculation, but were undetectable in non-irradiated and irradiated mice after Day 56, and in irradiated mice after Day 35. This decrease coincided with a significant reduction in both the numbers of bovine cells in the peritoneal cavity, and in the levels of bovine Ig detected in the sera. Bovine IgG and bovine IgM were detected in both normal and irradiated PBL-SCID-bo by 4 days after PBL injection, and remained detectable to 8 weeks after inoculation. T-cells appeared to be the predominant bovine cell population in the spleens. In a small proportion of both normal and irradiated PBL-SCID-bo, spleens three to 20 times the size of a normal SCID mouse spleen were observed. Relatively high levels of bovine cells were detected in the thymuses of some irradiated PBL-SCID-bo. Sporadic, low levels of bovine cells were observed in the mesenteric lymph nodes, peripheral blood, and kidneys of normal and irradiated mice, and in the lungs and livers of non-irradiated but not irradiated PBL-SCID-bo. Sublethal gamma irradiation of SCID recipients appeared to enhance engraftment of bovine cells into the murine spleen and thymus.