Research lines

Characterization of alternative complement pathway regulator Factor H and Factor H related proteins

Factor H (FH) is an abundant plasma glycoprotein, and is the main regulator of the alternative complement pathway. FH serves as a cofactor for Factor I (FI) in the inactivation of C3b to iC3b and has decay-accelerating activity towards C3 convertases. FH binds to host cell surfaces, by binding to host specific glycosaminoglycans (GAGs) on the cell surface following initial complement activation and targets C3b to inhibit further complement activation. Dysfunctional FH may lead to severe inflammatory disease due to uncontrolled complement activation on the endothelial cells of the vasculature. As the major inhibitor of the alternative pathway of complement, FH may potentially be used as therapeutic agent for several complement mediated human diseases.

We have developed a purification strategy to isolate functional FH from human plasma. In addition, in close collaboration with Prof. T.W. Kuijpers (AMC-UMC) and Dr. T. Rispens (Sansquin) we have developed several antibodies against FH and Factor H Related proteins (FHRs). We investigate FH and FHRs levels and function in health and disease. In addition, we have developed a novel specific monoclonal antibody that potentiates the function of FH on human cell surfaces.

Complement activation and regulation on red blood cells

All healthy human cells are equipped with several surface complement regulators to prevent damage through unwanted complement activation. Endothelial cells and blood cells are particularly well protected, as these are constantly exposed to the complement system in plasma. Red blood cells (RBCs) bear all membrane complement regulators, except CD46, which is only expressed on nucleated cells

Various diseases are associated with complement mediated RBC destruction, which may be antibody mediated (autoimmune hemolytic anemia (AIHA), allo-immunization) or the result of defective complement regulation (atypical hemolytic syndrome (aHUS), paroxysmal nocturnal hemoglobinuria (PNH)). Disease severity and response to existing complement inhibiting therapeutics is variable in these patients. This illustrates the urgent need to better understand both the triggering mechanisms of complement activation in these diseases and how the balance of complement activation and regulation on different cell surfaces is maintained.

We are investigating how RBCs are protected from unwanted complement activation, both in normal and pathological conditions, e.g. in AIHA and PNH. To answer our research questions we make use of a human cell line (HAP1) that is genetically engineered by CRISPR/Cas9 technology to lose one or several complement regulators (collaboration with Dr. R. Spaapen, Sanquin). Furthermore, we use isolated RBCs from healthy donors and PNH patients and plasma samples of AIHA patients.