Immunology scares many students. Receptors. Cytokines. Clusters of differentiation.
But here is the secret: Only a handful of concepts appear again and again on USMLE.
Master these three, and you will answer 80% of immunology questions correctly.
1. The Complement Cascade – Simplified
You do not need to memorize every single protein.
Know this:
- Classic pathway = Antibody-dependent (IgG or IgM)
- Alternative pathway = No antibody needed (bacterial surfaces)
- Lectin pathway = Mannose-binding lectin
High-yield fact: C3b = opsonization. C5a = inflammation and chemotaxis. C5-C9 = MAC (lysis).
Tested as: Recurrent pyogenic infections + low C3 + normal C4 = alternative pathway defect. Low C3 + low C4 = classic/lectin pathway defect.