C5AR1 and plexiform neurofibroma: In cultured primary human SCs from normal nerve or neurofibroma, expression of mRNA encoding C5 and C5aR1/R2 was low; C5 and C5aR1/R2 mRNAs were present at higher levels in human nerve and human PNF tissue samples, indicating that complement and complement receptor expression is largely in cells of the tumor microenvironment (Fig 1B).