Intraperitoneal transfer of wild-type bone marrow repopulates tissue macrophages in the Csf1r knockout rat without contributing to monocytopoiesis.

Homozygous null mutation of the Csf1r gene (Csf1rko) in rats leads to the loss of most tissue macrophage populations and pleiotropic impacts on postnatal growth and organ maturation leading to early mortality. The phenotype can be reversed by intraperitoneal transfer of wild-type bone marrow cells (BMT) at weaning. Here we used a Csf1r-mApple transgenic reporter to track the fate of donor-derived cells. Following BMT into Csf1rko recipients, mApple +ve cells restored IBA1 + tissue macrophage populations in every tissue. However, monocytes, neutrophils and B cells in bone marrow, blood and lymphoid tissues remained of recipient (mApple -ve ) origin. An mApple +ve cell population expanded in the peritoneal cavity and invaded locally in the mesentery, fat pads, omentum and diaphragm. One week after BMT, distal organs contained foci of mApple +ve , IBA1 -ve immature progenitors that appeared to proliferate, migrate and differentiate locally. We conclude that rat bone marrow contains progenitor cells that are able to restore, replace and maintain all tissue macrophage populations in a Csf1rko rat directly without contributing to the bone marrow progenitor or blood monocyte populations. This article is protected by copyright. All rights reserved.