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.

Selon les facteurs solubles de l’environnement (cytokines), les monocytes peuvent se différencier en macrophages (Mφ) ou en cellules dendritiques. Mes travaux de thèse montrent que l’IL-34, un second ligand du M-CSF-R (c-fms ou CD115), induit la différenciation de monocytes humains en macrophages CD14+ CD163+ (IL-34-Mφ), phénotypiquement et fonctionnellement similaires aux M-CSF-Mφ et aux macrophages associés aux tumeurs (TAM) isolés du cancer de l’ovaire. Ils possèdent des propriétés immunosuppressives et diminuent la prolifération des lymphocytes T CD4+ activés. Comme les Mφ orchestrent la réponse immunitaire, j’ai évalué la capacité des M-CSF-Mφ, IL-34-Mφ et des TAM à polariser les LT CD4+ mémoires. Les résultats montrent qu’ils polarisent des LT non-Th17 mémoires en LTh17 CCR4+ CCR6+ CD161+ conventionnels exprimant ou non de l’IFN. Ce processus est médié par l’expression constitutive de l’IL-1α membranaire exprimées sur ces macrophages.Dans le but d’identifier des stratégies pour prévenir l’accumulation de ces Mφ dans le cancer, j’ai montré que (i) l’IFNγ et le GM-CSF inhibent la différenciation des M-CSF-Mφ et IL-34-Mφ et que (ii) l’IFNγ permet la réversion des M-CSF-Mφ et IL-34-Mφ en Mφ immunostimulants. En conclusion, mes travaux montrent que les M-CSF-Mφ, IL-34-Mφ et les TAM, considérés initialement comme anti-inflammatoires, induisent la génération de lymphocytes Th17 via une expression constitutive de l’IL-1α. Ce processus pourrait contribuer à maintenir, localement, une inflammation modérée nécessaire au développement tumoral. / According to the soluble factors in the environment (cytokines), monocytes differentiate into macrophages (Mϕ) or dendritic cells. This project demonstrates that IL-34, a second ligand of the M-CSF receptor (c-fms or CD115), induces the differentiation of human monocytes into CD14high CD163 high Mφ (IL-34-Mφ), phenotypically and functionally similar to M-CSF-Mφ and to tumorassociated macrophages (TAM) isolated from the ovarian cancer. They exhibit potent immunosuppressive properties and decrease the proliferation of stimulated Tcells. As Mφ orchestrate the immune response, I have evaluated the capacity of M-CSF-Mφ, IL-34-Mφ and TAM to polarize human memory CD4+ T cells. Unexpectedly, results showed that they switch non- Th17 memory CD4+ T cells into conventional CCR4+ CCR6+ CD161+ Th17 cells, expressing or not IFNγ. This process is mediated by the constitutive expression of membrane IL-1α on these Mϕ subsets. In an attempt to identify strategies to prevent an accumulation of immunomodulatory Mϕ in cancer, I have shown that (i) IFNγ and GM-CSF prevent M-CSFandIL-34-induced monocyte differentiation into immunosuppressive Mφ and (ii) that IFNγ switchesestablished M-CSF-Mφ and IL-34-Mφ into immunostimulatory Mφ. In conclusion, this study demonstrates that human MCSF- Mφ, IL-34-Mφ and TAM initially considered as antiinflammatorycells, induce in vitro Th17 cell generation via a constitutive expression of membrane IL-1α. This process may contribute to maintain locally a restrained and smoldering inflammation required for angiogenesis and metastasis in tumors.