ERBB4 and schizophrenia: Although we did not find an altered expression of ErbB2/ErbB3 receptors in schizophrenia, it cannot be excluded that the observed cytokine profile following NRG1 stimulation is at least partially due to the abnormal activation of ErbB2/ErbB3 receptors, and not only ErbB4 with reduced expression is responsible for the effect.