The complement system is a complex, tightly regulated protein cascade involved in
pathogen defense and the pathogenesis of several diseases. Thus, the development of
complement modulators has risen as a potential treatment for complement-driven inflammatory
pathologies. The enzymatically inactive MAP-2 has been reported to inhibit the lectin
pathway by competing with its homologous serine protease MASP-2. The membrane-bound
complement inhibitor CD55 acts on the C3/C5 convertase level. Here, we fused MAP-2
to the four N-terminal domains of CD55 generating a targeted chimeric inhibitor to
modulate complement activation at two different levels of the complement cascade.
Its biological properties were compared in vitro with the parent molecules. While
MAP-2 and CD55 alone showed a minor inhibition of the three complement pathways when
co-incubated with serum (IC50MAP-2+CD55 1-4 = 60.98, 36.10, and 97.01 nM on the classical,
lectin, and alternative pathways, respectively), MAP-2:CD551-4 demonstrated a potent
inhibitory activity (IC50MAP-2:CD55 1-4 = 2.94, 1.76, and 12.86 nM, respectively).
This inhibitory activity was substantially enhanced when pre-complexes were formed
with the lectin pathway recognition molecule mannose-binding lectin (IC50MAP-2:CD55
1-4 = 0.14 nM). MAP-2:CD551-4 was also effective at protecting sensitized sheep erythrocytes
in a classical hemolytic assay (CH50 = 13.35 nM). Finally, the chimeric inhibitor
reduced neutrophil activation in full blood after stimulation with Aspergillus fumigatus
conidia, as well as phagocytosis of conidia by isolated activated neutrophils. Our
results demonstrate that MAP-2:CD551-4 is a potent complement inhibitor reinforcing
the idea that engineered fusion proteins are a promising design strategy for identifying
and developing drug candidates to treat complement-mediated diseases.
