While it is likely that this correlation is driven largely by the fact that the majority of complement gene expression in gliomas is derived from tumor-associated macrophages and microglia, cell types known to be enriched in hypoxic tumor areas (32), our experimental work established that at least C3 and C3AR1 could be directly induced in numerous cell types when cultured under hypoxic conditions. This evidence concerns the gene C3 and glioma.