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