AQP4 and neuromyelitis optica: Hence, while HEK cells offer very convenient features, such as high transfection efficiency and levels of expression of heterologous human AQP4, a drawback of using these cells in NMO diagnostic assays is also evidenced in the present work: specifically, the expression of integrin proteins in their membrane seems to elicit the binding of natalizumab antibodies that, in turn, can be recognized by human anti-IgG antibodies and result in a false signal for NMO diagnosis.