The Paul-Bunnell test detects heterophile antibodies in infectious mononucleosis. These antibodies agglutinate sheep RBCs but are absorbed by beef RBCs (not by Forssman antigen on guinea pig kidney cells). This pattern distinguishes heterophile antibodies from:

• A Forssman antibodies in normal serum (absorbed by guinea pig kidney but not beef cells) ✓
• B Antibodies in serum sickness (absorbed by guinea pig kidney, not beef cells)
• C Anti-EBV VCA IgM antibodies measured by ELISA
• D Cold agglutinins in Mycoplasma pneumoniae infection

Explanation

In the Paul-Bunnell Davidson differential absorption test, the source of heterophile antibodies is identified by their absorption pattern. Forssman antibodies (found in normal serum) are absorbed by guinea pig kidney (which contains Forssman antigen) but not by beef RBCs. Infectious mononucleosis (EBV) heterophile antibodies are absorbed by beef RBCs but NOT by guinea pig kidney — distinguishing them from Forssman antibodies. Serum sickness antibodies are absorbed by guinea pig kidney. This differential absorption is the basis of the classical Paul-Bunnell-Davidson test; modern monospot tests use horse RBCs for rapid testing.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.