Role of macrophage colony stimulating factor-1 (CSF-1) in postnatal growth
Gow, Deborah Jane
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Colony-Stimulating Factor (CSF-1) is required for the proliferation, differentiation and survival of cells of the mononuclear phagocyte lineage. Mice with a mutation in their CSF-1 gene demonstrate abnormal development in many organ systems and severe growth retardation. These defects can be corrected by administration of rh- CSF-1, and when similarly administered to wild-type mice, can increase organ and body weight, thus highlighting the importance of CSF-1 in postnatal growth. CSF-1 is known to be elevated in the circulation in the immediate postnatal period of both mice and humans. It remains to be seen whether CSF-1 deficiency underlies important clinical issues such as low birth weight, and whether there are any functionally important variations in expression or biology of CSF-1, or the alternative CSF-1R ligand IL-34 that contributes to variation in somatic growth between individuals. This thesis aimed to use the pig as a model for human innate immunity and disease based upon recent publications that highlighted the similarities in their immune systems. To investigate the effects of CSF-1 on postnatal growth the first aim was to characterise the CSF-1R system in pigs and produce reagents. Biologically active porcine CSF-1 and IL-34 were produced along with expression of full length functional porcine CSF-1R and production of anti-CSF-1R antibodies. A bioassay was developed and optimised to assess the biological activity of these proteins. The cross-species reactivity of a range of species CSF-1 and IL-34 proteins was investigated in-vitro using the bioassay and cell culture systems. Recombinant CSF-1 is known to have a short half-life. Since conjugation of proteins to the Fc region of immunoglobulins has been used extensively to improve circulating half-life; a porcine Fc CSF-1 fusion protein was generated by commercial partners, Pfizer Animal Health. The conjugated and un-conjugated CSF-1 proteins had identical activity in cell line and primary cell assays in-vitro. The in-vivo activity of porcine Fc CSF-1 was tested initially in the Csf1r-EGFP+ mouse reporter line and C57BL/6 mice. The Fc CSF-1 protein was more active than the native protein in promoting increased monocyte and tissue macrophage numbers, increasing body weight and inducing hepatosplenomegaly. Hepatic growth was associated with extensive macrophage infiltration and hepatocyte proliferation, identified by gene expression profiling as well as immunohistochemistry. Fc CSF-1 was then tested in neonatal pigs. They were found to have an immature immune system that develops with age. No postnatal surge of CSF-1 was detected. Fc CSF-1 administration increased blood monocyte and neutrophil numbers confirming that CSF-1 is not saturating at this time. Nevertheless, no influence on postnatal growth rate was identified. This is discussed in terms of the differences in placental architecture in the pig compared to human and mouse. This thesis demonstrates the effectiveness of porcine Fc CSF-1 in both mice and porcine and highlights the important role that CSF-1 and macrophages play in liver homeostasis. Fc CSF-1 is identified as candidate therapeutic agent in humans and companion animals for tissue regeneration, and a tool for the study of the role of macrophages in physiology and pathology.