KINETICS OF CENTRAL-NERVOUS-SYSTEM MICROGLIAL AND MACROPHAGE ENGRAFTMENT - ANALYSIS USING A TRANSGENIC BONE-MARROW TRANSPLANTATION MODEL

To determine the kinetics of tissue macrophage and microglial engraftm ent after bone marrow (BM) transplantation, we have developed a model using the ROSA 26 mouse. Transplanted ROSA 26 cells can be precisely i dentified in recipient animals because they constitutively express bet a-galactosidase (beta-gal) and neomycin resistance. B6/129 F2 mice wer e irradiated and transplanted with BM from ROSA 26 donors and their ti ssues (spleen, marrow, brain, liver, and lung) examined at various tim e points to determine the kinetics of engraftment. Frozen sections fro m transplanted animals were stained histochemically for beta-gal to id entify donor cells. At 1, 2, 6, and 12 months posttransplantation, 98% to 100% of granulocyte-macrophage colonies were of donor (ROSA 26) or igin determined by beta-gal staining and by neomycin resistance. Splen ic monocytes/macrophages were 89% donor origin by 1 month confirming q uick and complete engraftment of hematopoietic tissues. At this time, only rare ROSA 26 tissue macrophages or microglia were observed. Alveo lar macrophage engraftment was evident by 2 months and had increased t o 61% of total tissue macrophages at 1 year posttransplantation. The k inetics of liver Kupffer cell engraftment were similar to those seen i n the lung. However, donor microglial engraftment remained only 23% of total microglia at 6 months and increased to only 30% by 1 year. Also , donor microglia were predominantly seen at perivascular and leptomen ingeal, and not parenchymal, sites. The data show that microglia deriv e from BM precursors but turn over at a significantly slower rate than other tissue macrophages. No clinical or histological graft-versus-ho st disease was observed in the recipients of ROSA 26 BM. These kinetic s may impact strategies for the gene therapy of lysosomal storage dise ases. Because individual donor cells can be identified in site, the RO SA 26 model should have many applications in transplantation biology i ncluding studies of homing and differentiation. (C) 1997 by The Americ an Society of Hematology.