<prompt> Which of the following is an example of heterophile antibody test ?Widal testWeil-Felix reactionRose-waler testBlood grouping cross matching  <response>: Ans. is b i.e., Weil-Felix reaction Heterophilic agglutination reaction Some organisms of different class or species share closely related antigens. When serum containing agglutinin antibody of one organism gives agglutination reaction with antigen of other organism, it is called heterophilic agglutination test. Examples are Streptococcus M.G. agglutination test for primary atypical pneumonia. Weil - Felix reaction for typhus fever. Paul Bunnell test for IM1V. 