FOLR1 and neoplasm: First, degranulation assays, using human FcεRI-expressing RBL SX-38 mast cells demonstrated that tumour-associated antigen-specific IgE antibodies, MOv18 and anti-Her2 (trastuzumab) IgE, did not induce RBL SX-38 degranulation unless cross-linking was achieved by polyclonal anti-IgE, or in the case of MOv18 IgE, by the formation of an immune complex with recombinant FRα antigen and anti-FRα polyclonal antibody.