<prompt> Prausnitz-kustner PK reaction was used to demonstrate -IgAIgGIgMIgE  <response>: Ans. is d i.e., IgE o IgE is homocytotropic i.e. species specific. Only human IgE can fix to the surface of human cells. This is the basis of the Prausnitz-Kustner PK reaction, which was the original method for detecting atopic antibody. 