Mycoplasma pneumoniae atypical pneumonia is associated with a specific cold agglutinin. These cold agglutinins are IgM antibodies directed against:

• A Mycoplasma membrane lipoproteins (P1 adhesin)
• B I antigen on human red blood cells (modified by Mycoplasma neuraminidase) ✓
• C Forssman antigen on sheep erythrocytes
• D Galactocerebroside in peripheral nerve myelin

Explanation

In Mycoplasma pneumoniae infection, IgM cold agglutinins (maximum activity at 4°C) develop in approximately 50% of patients, particularly those with severe infection. These IgM antibodies target the I antigen on human erythrocytes — a branched carbohydrate antigen that becomes altered or cross-reacts due to Mycoplasma-induced neuraminidase activity (exposing the I antigen or producing antibodies that cross-react). Cold agglutinins cause reversible red cell agglutination at cold temperatures; clinical haemolysis is rare. Forssman antigen is involved in the Paul-Bunnell test (infectious mononucleosis EBV); galactocerebroside antibodies are in Guillain-Barré after Campylobacter infection.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.