This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
Passive cutaneous anaphylaxis detect: 
Select and explain. 
A. Heterocytotropic ab, B. Wheal and flare reaction, C. Atopy, D. Cutaneous anaphylaxis
A: Heterocytotropic ab
Answer: A: Heterocytotropic ab 
Explanation: Ans. (a)Passive cutaneous anaphylaxis-in vivo method for detection of antibodies.Antigen injection intradermally then same antigen with a dye injected IV - after 4 to 24 hours - wheal flare reaction occurs in intradermal site.Helps to detect IgG ab which is heterocytotropic, not for IgM which is homocytotropic.