Factor H is a pivotal complement regulatory protein that is preferentially produced by the liver and circulates in high concentrations in serum. There has been an increasing interest in the... Show moreFactor H is a pivotal complement regulatory protein that is preferentially produced by the liver and circulates in high concentrations in serum. There has been an increasing interest in the extrahepatic production of comple-ment factors, including by cells of the immune system, since this contributes to non-canonical functions of local complement activation and regulation. Here we investigated the production and regulation of factor H and its splice variant factor H-like protein 1 (FHL-1) by human myeloid cells. As validation, we confirmed the pre -dominant presence of intact factor H in serum, despite a strong but comparable mRNA expression of CFH and FHL1 in liver. Comparable levels of CFH and FHL1 were also observed in renal tissue, although a dominant staining for FHL-1 was shown within the proximal tubules. Human in vitro generated pro-and anti-inflammatory macrophages both expressed and produced factor H/FHL-1, but this was strongest in pro-inflammatory macro-phages. Production was not affected by LPS activation, but was increased upon stimulation with IFN-gamma or CD40L. Importantly, in both macrophage subsets mRNA expression of FHL1 was significantly higher than CFH. More -over, production of FHL-1 protein could be confirmed using precipitation and immunoblotting of culture su-pernatants. These data identify macrophages as producers of factor H and FHL-1, thereby potentially contributing to local complement regulation at sites of inflammation. Show less
Transplantation is the golden standard for the treatment of end-stage renal disease. During this process, the transplanted organ is often damaged. In this thesis, we investigated whether activation... Show moreTransplantation is the golden standard for the treatment of end-stage renal disease. During this process, the transplanted organ is often damaged. In this thesis, we investigated whether activation of the complement system, part of our innate immune system, plays a local role. We reviewed that properdin, the only known positive regulator of the complement system, was detected in serum, plasma and urine from patients with various complement-mediated renal diseases. In protocol biopsies obtained 10 days after transplantation, properdin was found deposited in addition to complement activation markers. Next, we showed that dendritic cells secrete properdin and a decrease in properdin levels during dendritic cell- T-cell interaction resulted in reduced T-cell proliferation and activation. We also showed that properdin is able to bind to surfaces of both viable and dead cells, contributing to complement activation. Macrophages can also produce properdin and negative regulators factor H and its splice variant FHL-1. Increasing knowledge on complement factor production by other cells than hepatocytes, including immune cells, hints towards a local role of the complement system in various processes. These findings contribute to a better understanding of the local role of the complement system and are important for the applications of (new) complement-inhibiting drugs. Show less
Dixon, K.O.; O'Flynn, J.; Klar-Mohamad, N.; Daha, M.R.; Kooten, C. van 2017
The complement system has been shown to have a role in various systemic autoimmune (AI) diseases which have a renal component. This includes systemic lupus erythematosus (SLE), goodpastures... Show moreThe complement system has been shown to have a role in various systemic autoimmune (AI) diseases which have a renal component. This includes systemic lupus erythematosus (SLE), goodpastures syndrome and anti-neutrophil cytoplasmic antibody (ANCA) associated vasculitides. In particular the classical pathway (CP) of complement is involved in SLE, with the exact mechanism of how these SLE autoantigens along with their autoantibodies interact with complement in the glomerulus remaining ambiguous. Furthermore, recent studies have demonstrated the expanding role of the alternative pathway (AP) of complement activation in steady state or in aspects of ANCA associated vasculitides or anti-GBM disease. The precise means of activation of the AP in these immune complex mediated disease settings remains unclear. Regulation is imperative in the AP due to its inherent ability to autoactivate. Factor H and properdin are both key opposing regulators in the AP with novel emerging roles in initiation and control of the AP. Deciphering the specific modes of AP activation and involvement is an ever expanding field requiring further elucidation, with previously unexpected roles for AP components revealing the diversity and complexity of this ancient pathway. Show less
